NANI Demo Booklet Ver 0.03 Jan 2015

8/17/2019 NANI Demo Booklet Ver 0.03 Jan 2015

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Physics Demonstrations Anveshika

National Anveshika Network of India (NANI)

Version 0.03, January 1, 2015


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cNOTICE: “This material is protected by copyright and has been copiedsolely for the non-commercial educational purposes. You may not sell, alter orfurther reproduce or distribute any part of this material to any other person.Where provided to you in electronic format, you may only print from it for

your own private study and research. Failure to comply with the terms of this warning may expose you to legal action for copyright infringement and/ordisciplinary action by the copyright holders of original work.”

ACKNOWLEDGMENT: Our sincere gratitude to,

(a) Dr H C Verma, Coordinator, National Anveshika Network of India(NANI). He is the driving force for Anveshika activities.

(b) Shiksha Sopan, IIT Kanpur

(c) Utsahi Physics Teachers, www.utsahiphysicsteachers.com

(d) Dr Ajay Mahajan, Dayanand Science College, Latur, Maharashtra

(e) Anveshika Coordinators and their team members:

Kanpur SGM Amit Kumar BajpayiAgra Raman R K Awasthi

Siwan Siwan Mr. Rajeev RanjanKolkata TAXXILA Dr. Amit Kumar JanaLucknow Mitra Dr. R. K MitraPatna Patna Dr Amarendra NarayanOraiya Go&go Brajesh DixitMunger VSS Dr. K N RaiKolhapur GCG Dr S A MastiBhilkwadi SSB Dr Gajanan PatilPilibhit Samadhan Dr Laxmi Kant SharmaPilani BPS Mr Manoranjan K SinghHissar OPJS Lalit Mohan SinghDelhi BVN Pragya NopaniUdhampur Happy MineeshVizianagram Focus Chandrasekhar JogaChandigarh SGGSC Dr M S MarwahaDhanbad Vidya Arvind Kumar PathakHyderabad ViBha Jitender Singh

DISCLAIMER: Although most of the science activities presented here are re-garded as low hazard, we disclaim all liability for any occurrence, including,but not limited to, damage, injury or death which might arise as consequencesof the use of any experiment(s) listed or described here. Therefore, you assumeall the liability and use these science activities at your own risk!

http://www.utsahiphysicsteachers.com/http://www.utsahiphysicsteachers.com/


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Dedicated to those who appreciate Physics and the work of Dr. H. C. Verma


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Contents

Contents iii

I Mechanics 1

1 Measure Speed of the Ant 3

2 Reaction Time 4

3 How Much is One Newton? 5

4 Pull the Paper under the Tumbler 6

5 Balancing the Nails 7

6 A drop of Water Makes Slides Stick Together 8

7 Get Going Mug 9

8 Action-Reaction forces in Newtons Third Law 10

9 Check Newton’s Law for interaction between two RingMagnets 11

10 Resonance and Sound Waves 12

11 The Physics of Lever and Mechanical Advantage 13

12 Weightlessness with slinky 14

13 Which thread breaks first? 15

14 A Magical Coin 16

15 Lift a Weight by Moving another Weight in a Circle 17

16 Key-bottle experiment 18

17 Spring Potential Energy 19

18 Calibrating a Non-Linear Spring 20

Corrections/Suggestions to: [email protected] iii

http://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]


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iv Contents

19 Linear Momentum of the Ball 21

20 Why Does it Goes Up? 22

21 Counter-intutive Centre of Mass with Bottle 23

22 Balancing the Scale on Fingers 24

23 To find Centre of Mass of a Rectangular Shape 25

24 To Find the Coefficient of Restitution 26

25 It is not Easy to Do Simple Movements! 27

26 Win a 100 Rs Note 28

27 Self Balancing Toy 29

28 Rolling and Kinetic Friction 30

29 Gyroscope from cycle wheel 31

30 To study the theorem of perpendicular axes in Moment

of Inertia 33

31 Paper Helicopter 34

32 Gyroscope Using Toy Motor 35

33 Coupled Pendulum 36

34 SHM Phase and Phase Difference 37

35 Resonance in pendulum by hand 39

36 To Study Torsional Oscillation of a Rectangular Body 40

37 Why Balloons come Closer? 41

38 Why the fluid does not comes out? 42

39 Suspending a Cup by a Balloon 43

40 Keep the Paper Dry in Water 44

41 Push Water in a pair of Connected Syringes 45

42 Blow Air in a Long Air Bag 46


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Contents v

43 To find the atmospheric pressure using a syringe andweights 47

44 To measure the viscosity of water 48

45 Archimedes Principle 49

46 Effect of Soap on Surface Tension 50

47 Rise of Paper (Welcome) due to surface tension 51

48 Pressure in Two Balloons connected by transparent pipe 52

49 The Fun of Three Bottles 53

50 Rising of water due to centrifugal force! 54

51 To study the extension-load characteristics of bicyclevalve tube 55

52 To study torsional oscillations of a wire 56

II Waves 57

53 Vibrations, Rerefaction and Compression in a Long Spring! 59

54 Visualize Wave Motion 60

55 Compression and Rarefaction in Longitudinal Waves 61

56 Sound is Produced by Vibrations 62

57 Reflection of Sound 63

58 Visualize your Sound! 64

59 The Phenomenon of Beats! 65

60 The Optics of Waves on Water Surface 66

61 Interference with thread! 67

62 Diffraction of light from a thin wire! 68

63 Interference in Ripple Tank! 69


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vi Contents

IIIOptics 71

64 Multiple Images with Plane Mirrors 73

65 Scattering of Lights of Different Colours 74

66 Scattering of Light 75

67 Dispersion of Light by a Prism 76

68 Tracing the Ray of Light through a Prism? 77

69 Advantage of having Two Eyes? 78

70 Image formed by a Convex Lens 79

71 Reflection from Curved Surface 80

72 Focal Length of a Concave Mirror 81

73 Nature of the Image formed by a Concave Mirror 82

74 Rising of the Coin due to Refraction 83

75 Refraction through a Glass Slab 84

76 Trace the Path of a Ray through Glass Slab 85

77 Refraction Through a Glass of Water 86

78 Measuring the Focal Length of a Convex Lens 87

79 Total Internal Reflection in a Dettol Bottle 88

80 Focal Length of a Parabolic Reflector! 90

81 Laws of Reflection of Light! 91

82 To Deduce Refractive Index of a Glass Slab 92

83 To Visualize a Light Ray 93

84 To Find Focal Length of a Concave Lens 94

85 To Find Refractive Index of a Liquid 95

86 To study the variation of image position for object atinfinity with incident angle 96


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Contents vii

87 Where did the Coin come from? 97

88 Polarization of Light! 98

89 Variation of refractive index with wavelength 99

90 Variation of Intensity with Distance! 100

IVThermodynamics 101

91 Burning Candle in Limited Air 103

92 Why Does Water not Fall? 104

93 Own Thermometer 106

94 Saturated Salt Solution 107

95 Why does Water rise in Burning Candle Experiment? 108

96 Boyles law using a syringe and weights 110

97 Boil Water with Hands! 111

98 Cloud in a Bottle! 113

99 Measure dew point in your room 114

100 Coffee cup calorimetry 115

101 See Convection Current in Air 116

102 Conduction of Heat 117

103 Solar Heating 118

104 Boiling Water in Paper Cup 119

V Electromagnetism 121

105 The Rotating Straw 123

106 Bending of Water Stream due to Electrostatic Charges 125

107 Electrostatics of Hanging Balloons 126

108 Which Direction is Electric Field? 127


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viii Contents

109 Direction of electric field 128

110 Electric potential in a capacitor 129

111 Playing with capacitors made from kitchen Utensils 130112 Charging and discharging capacitors 132

113 Verification of Ohm’s Law 134

114 Series Connection of Resistors 135

115 Parallel Connection of Resistors 136

116 Wheatstone bridge using electric bulbs! 137

117 Measure the Resistance of an Electric Bulb 138

118 Magnetic Line of Forces 139

119 Motion of Charged Particles in Magnetic Field 140

120 Magnetic Effect of Current 142

121 Magnetic Field due to a Straight Conductor 143

122 Making of an Electromagnet 144

123 Magical Swing 145

124 Attraction and Repulsion between Current Carrying Con-ductors! 146

125 Current detector 147

126 Poles of a Ring Magnet 148

127 Magnetic Shielding 149

128 Magnetic field lines for a given magnet 150

129 Force law between two magnets as a function of theirseparation 151

130 Effect of Temperature on Magnetic Materials 152

131 Faraday’s Law of Electromagnetic Induction 153

132 Inducing Current without a Magnet 154


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Contents ix

133 Make a Galvanoscope 155

134 Generating Energy with a Turbine 156

135 Three Pole Magnet 157

136 Put Me Off! 158

137 The Mother Coil! 160

138 Force due to eddy currents 161

139 A Magnet Falling Through Conducting Tube 162

140 How to slow a Rotating Conducting Disk? 164

141 Naughty Coil! 165

142 Visualize Alternating Current 166

143 To Study Effect of Core on RL Circuit 167


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Part I

Mechanics

1


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Demonstration 1

Measure Speed of the Ant

cbaThe theme of this activity is motion and mea-surement of distance. The distance of a straightline is usually measured with a scale. This ac-tivity train students on how to measure distanceof a curved line.

Watch an ant moving on the floor. Keepmarking ant position as it moves. Measure thedistance it travels and the time it takes to travelthis distance. Calculate the speed of the ant.

References

[1] Source: H.C. Verma, Foundation Science Physics for Class 9 , 3rd Edition (2006), Page 39, Bharati Bhawan

Corrections/Suggestions to: [email protected] 3

http://localhost/var/www/apps/conversion/dbAb/a/ba/cba.padhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/dbAb/a/ba/cba.pad


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Demonstration 2

Reaction Time

jdaThe distance an object falls in the gravitationalfield of the earth can be used as a sensitivemeasure of short time intervals. This demo isbased on kinematic equation s = ut + 12 at

2.The usual demonstration consists of holding ameter stick vertically from the top while a vol-unteer stands poised ready to catch it betweenthe thumb and forefinger. If the fingers are op-posite the 50 cm mark, for example, when themeter stick is dropped, the position of the fingers when the meter stickis caught gives a measure of the distance the meter stick fell before thevolunteer could react. The time is then calculated from t =

2s/g, where

g = 9.8 m/s2 and s is the distance dropped (in meters).If s = 20 cm then we get t = 0.2 s = 200 ms.

References

[1] Source: http://sprott.physics.wisc.edu/demobook/CHAPTER1.HTM

4 Corrections/Suggestions to: [email protected]

http://localhost/var/www/apps/conversion/dbAb/a/da/jda.padhttp://sprott.physics.wisc.edu/demobook/CHAPTER1.HTMhttp://sprott.physics.wisc.edu/demobook/CHAPTER1.HTMhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://sprott.physics.wisc.edu/demobook/CHAPTER1.HTMhttp://sprott.physics.wisc.edu/demobook/CHAPTER1.HTMhttp://localhost/var/www/apps/conversion/dbAb/a/da/jda.pad


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Demonstration 3

How Much is One Newton?

aaaTake a weighing machine where the object isplaced on the platform and the mass is displayedon a dial or on a digital display. See the read-ing, if it has any zero error, remove it. Withoutseeing the reading, press the pan of the weigh-ing machine by a force which you think is 1 N.Now, see the reading and adjust the push till thedial reading shows 100 g which is approximately1 N. What is the maximum force you can pusha balance kept on the ground?

References

[1] Source: http://www.vigyanprasar.gov.in/activity_based_science/Expm1.htm

[2] Source: H.C. Verma, Foundation Science Physics for Class 9 (3rd ed.),

Page 72, Bharati Bhawan, 2006


http://localhost/var/www/apps/conversion/dbAb/a/aa/aaa.padhttp://www.vigyanprasar.gov.in/activity_based_science/Expm1.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm1.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.vigyanprasar.gov.in/activity_based_science/Expm1.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm1.htmhttp://localhost/var/www/apps/conversion/dbAb/a/aa/aaa.pad


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Demonstration 4

Pull the Paper under the Tumbler

kbaNewtons three law of motion are taught in school from quite early times.Though students know the statements of the three laws but when it comesto application, quite often the laws are wrongly interpreted. The experi-ment described is quite common and is shown to dramatize the concept of Newtons 1st law of motion or inertia. However, a detailed analysis revealsgreater insight into the laws.

Near the edge of a table, place a glass tum-bler filled with water. Now hold the part of the paper overhanging from the table using bothhands. Give a sharp jerk to the paper and pull itquickly. What you find is that the paper comesout from below the glass and the glass just stays on the table with no wa-ter spilling out. Try pulling the paper with different speeds and see whathappens.

The common explanation is that because of inertia, the glass remainsat its place and the paper comes. But is it the explanation? Where doesthis inertia go, when the paper is pulled slowly? Does inertia dependon velocity? It is friction, acceleration and distance moved under thisacceleration that have to be roped in for proper understanding.

Variants: A coin placed on the playing card kept above the glass. Whenplaying card is pushed, the coin fall into the glass. Another variant By DrAjay Mahajan is “Jiddi Sikka” demo.

References

[1] Source: http://utsahiphysicsteachers.com/resourcematerial/experiments/Mechanics/Pullpaper.htm

[2] Video: http://youtu.be/CSfqk9BIb5k?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrX


http://localhost/var/www/apps/conversion/dbAb/a/ba/kba.padhttp://utsahiphysicsteachers.com/resourcematerial/experiments/Mechanics/Pullpaper.htmhttp://utsahiphysicsteachers.com/resourcematerial/experiments/Mechanics/Pullpaper.htmhttp://youtu.be/CSfqk9BIb5k?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/CSfqk9BIb5k?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://youtu.be/CSfqk9BIb5k?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/CSfqk9BIb5k?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://utsahiphysicsteachers.com/resourcematerial/experiments/Mechanics/Pullpaper.htmhttp://utsahiphysicsteachers.com/resourcematerial/experiments/Mechanics/Pullpaper.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/kba.pad


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Demonstration 5

Balancing the Nails

lbaCan you balance 14 nails on a nailhead? Fixa nail on a piece of wood or some lid so that itremains vertical with its flat top up. We will callthis arrangement stand. Now, ask your friendsto balance the remaining 14 nails on the nailfixed to the stand. Your friends will be a realfix attempting to put so many nails in a very small space. But, you cometo their rescue by demonstrating how this can be done.

In this experiment the principle of centre of gravity plays its role. Ac-cording to this principle, due to the weight of the inclined nails on bothsides of the base nail the weight of the entire set-up acts below the bal-ancing point. Thus, the entire set of nails balances comfortably. You maygently lower the nails on one side and then remove your hand. This makesthe entire set-up quiver but it does not fall down.

Puzzle/Concepts: Ask students to pin-point centre of mass of the struc-ture when Nail are horizontal/slanted. Generally, students points at geo-metrical centre in first case. In second case, they do not give a thoughtabout third direction. The CM is out of the structure. Also, we can ex-plain about concept of stable/unstable equilibrium, torqe, potential energyetc.

References

[1] Source: http://www.vigyanprasar.gov.in/activity_based_science/Exp11.htm

[2] Arvind Gupta Video in Hindi, http://www.youtube.com/watch?v=lGMq460lRpY


http://localhost/var/www/apps/conversion/dbAb/a/ba/lba.padhttp://www.vigyanprasar.gov.in/activity_based_science/Exp11.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Exp11.htmhttp://www.youtube.com/watch?v=lGMq460lRpYhttp://www.youtube.com/watch?v=lGMq460lRpYhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.youtube.com/watch?v=lGMq460lRpYhttp://www.youtube.com/watch?v=lGMq460lRpYhttp://www.vigyanprasar.gov.in/activity_based_science/Exp11.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Exp11.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/lba.pad


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Demonstration 6

A drop of Water Makes Slides Stick Together

obaWe have read in books about cohesive and adhesive forces. When twoobjects made of the same material are in contact with each other, the forceacting between the molecules of the surfaces in contact is called cohesiveforce. However, when two objects of different materials remain in contact,the force between molecules of the surfaces in contact is called adhesiveforce. How strong are these forces? Sometimes they are so strong thatthey may appear to challenge even persons of great physical strength. Inthis experiment we shall use a drop of water to make two thin slides stickto each other, and study these forces.

In biology labs or diagnostic shops meantfor blood test, thin rectangular glass plates areused. These plates are called slides. Take twosuch slides. Place a drop of water on any of the slides. Keep the secondslide on the first moving the slides over each other, spread the water dropbetween them. Now by putting the slides with your hands try to separatethem out from each other. Remember you are not supposed to move theslides against each other in a sliding manner. Are you able to pull the slidesapart? You will not be able to do it as both the slides very strongly stickto each other.

Can we make a numerical example out of this? What is the typicalvalue of force given layer thickness, surface tension, area of slide etc?

References

[1] Source: http://www.vigyanprasar.gov.in/activity_based_science/Exp14.htm

[2] Video http://youtu.be/GlKYCnwFOPM?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrX


http://localhost/var/www/apps/conversion/dbAb/a/ba/oba.padhttp://www.vigyanprasar.gov.in/activity_based_science/Exp14.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Exp14.htmhttp://youtu.be/GlKYCnwFOPM?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/GlKYCnwFOPM?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://youtu.be/GlKYCnwFOPM?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/GlKYCnwFOPM?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://www.vigyanprasar.gov.in/activity_based_science/Exp14.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Exp14.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/oba.pad


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Demonstration 7

Get Going Mug

zbaTie a cup and a matchbox to the two ends of a 1.5 m long thread. Place a pencil at the cen-tre point of the thread, such that mug is at thelower end. Now bend the threadover the pencilso that both the objects are suspended. In aswift motion, release the matchbox. Somethingsurprising happens. The mug does not fall andbreak. Instead, the matchbox rotates and the thread winds itself aroundthe pencil a few times. This experiment is based on friction and angularmomentum.


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Demonstration 8

Action-Reaction forces in Newtons Third Law

ebaDo this activity to study action reaction forces.You will need two spring balances. When hookof a spring balance is pulled by a force, thespring inside it gets stretched. A pointer attached to the spring readsthe force on the scale of the spring balance.

Attach the ring of a spring balance (A) to a fixed support on a table.Pass the hook of the second spring balance (B ) through the hook of A.Now, pull B by its ring. Keep applying the same amount of pull while youtake readings.

Note the readings of A and B . These are equal. What do these readingsshow? The reading on A gives the magnitude of the force exerted on itshook, i.e., the force exerted by A. The fact that the readings are the sameshows that the force exerted by A on B and that exerted by B on A havethe same magnitude.

Can you say that these forces have opposite directions? Both the springsare stretched. To stretch the spring, the hook must be pulled away from thebalance. So B is exerting a force on A towards the right, and A is exerting

a force on B towards the left. So, the forces have opposite direction.

References

[1] Source: H.C. Verma, Foundation Science Physics for Class 9 (3rd ed.),Page 53, Bharati Bhawan, 2006


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Demonstration 9

Check Newton’s Law for interaction between two Ring Magnets

jbaA common statement for Newtons 3rd law reads as “for every action thereis always an equal and opposite reaction”. The important part which isgenerally missed out that it concerns the forces exerted by two bodies oneach other. This demo shows that forces exerted by two ring magnets areequal and opposite.

Take a PVC stand and two ring magnets.Weigh the two ring magnets, say A and B , and

the stand separately. Let the weights be W 1,W 2 and W 3. Put the first ring magnet A in thestand and place this stand on weighing machinepan, display of the weighing machine will showW 3 + W 1. After this put the other magnet B inthe same stand in such a way that it will be inthe repulsive mode with magnet A. The magnetB will be floating in the air having no verticalcontact force with anything. Still the dial reading will be W 1 + W 2 + W 3.

Although the magnet B is floating in air i.e., it is not on weighing pan andis stationary in air (i.e. net vertical force acting on B is zero), but the scalereading has increased by W 2. That means B is pushing A downwards bythe force W 2. Now, B is not falling so some force acts on it upwards tohold it there. This force is from magnet A only. So, magnet A is pushingB by a force W 2 upwards. Thus the two forces exerted by the two magnetson each other are equal and opposite.

References


[2] Video: http://youtu.be/gQvflRy43Pk?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrX


http://localhost/var/www/apps/conversion/dbAb/a/ba/jba.padhttp://www.vigyanprasar.gov.in/activity_based_science/Expm2.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm2.htmhttp://youtu.be/gQvflRy43Pk?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/gQvflRy43Pk?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://youtu.be/gQvflRy43Pk?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://youtu.be/gQvflRy43Pk?list=PLjVcSEe2pNnZiJpmGp9-iGmjkJzf4QGrXhttp://www.vigyanprasar.gov.in/activity_based_science/Expm2.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm2.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/jba.pad


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Demonstration 10

Resonance and Sound Waves

gcaThis experiment demonstrates forced vibrationsand resonance. Apparatus consists of a set of three pair of thin steel strips (e.g., hacksawblade) of different lengths fixed to a woodenblock. Metal strips of a pair are similar in colourand dimensions.

When a strip of a one colour is plucked, onlythe other strip of the same colour starts vibrating where as the strips of the other colours remain stationary showing that maximum energy is trans-ferred when resonance occurs.

The natural frequency of metal strip is given by ν = 2π

km , where k

is stiffness (it is a material property, equivalent of spring constant) and mis mass. The masses of strips of same length is equal and that of differentlength is unequal. Thus, natural frequency of strips of same length is equalbut that of different length is unequal.

This can also be used to demonstrate that waves (sound) moves through

solid base.

References

[1] Source: http://www.tarangscientificinstruments.com/products-mechanics.html


http://localhost/var/www/apps/conversion/dbAb/a/ca/gca.padhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://localhost/var/www/apps/conversion/dbAb/a/ca/gca.pad


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Demonstration 11

The Physics of Lever and Mechanical Advantage

hcaThis is a simple model to explain concept of lever arm (arm length), force, torque etc. Asmaller force applied at a greater distance fromthe axis of rotation can lift a larger weight.

References

[1] Source: http://www.tarangscientificinstruments.com/

products-mechanics.html


http://localhost/var/www/apps/conversion/dbAb/a/ca/hca.padhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://www.tarangscientificinstruments.com/products-mechanics.htmlhttp://localhost/var/www/apps/conversion/dbAb/a/ca/hca.pad


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Demonstration 12

Weightlessness with slinky

ldaThe objective of this demo is to get a feeling of the phenomena of weightlessness.

An effect of acceleration due to gravity (g) isthe extension in a slinky. As you must have ex-perienced, a slinky is like a spring but the turnsare very flexible and even without a load, itcan extend to several times of its natural length

under its own weight. If you hold few turnsof a slinky in your hand and let the rest of ithang from there, the hanging part also extendsthrough large distances. This extension againis because of g. If the effect of g can be reduced to zero, the slinky in avertical position will not extend.

Hold some of the turns of a slinky in one hand holding some of theturns in one hand. Let rest of it hang vertically. The hanging part will beextended. By holding appropriate number of turns make this part about10 cm. Now leave the slinky and let it fall. You may catch the falling slinkyat some lower level. The extended turns all shrink. You may do it severaltimes to show the effect clearly. The slinky shrinks because in the frameof the falling slinky, there is no effect of gravity. The slinky has becomeweightless as all measurable effects of weight have vanished.

You can also perform this demo with a spring-mass system. The springshould have small spring constant so that there is a large visible extensionwhen you hang a load. Dropping it will shrink the spring

References


[2] Youtube Slow Motion: http://youtu.be/eCMmmEEyOO0


http://localhost/var/www/apps/conversion/dbAb/a/da/lda.padhttp://www.vigyanprasar.gov.in/activity_based_science/Expm3.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm3.htmhttp://youtu.be/eCMmmEEyOO0http://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://youtu.be/eCMmmEEyOO0http://www.vigyanprasar.gov.in/activity_based_science/Expm3.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm3.htmhttp://localhost/var/www/apps/conversion/dbAb/a/da/lda.pad


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Demonstration 13

Which thread breaks first?

kfaIntroduction: To pluck a mango from a tree, we have to hold the mangoand give a jerk. If we pull gradually it may not get detached from the tree.We can also detach fruits from a tree giving a jerk to the branch on whichfruits have grown. This demonstration is similar to the above situation.What do you need: A stand, A long thread and a bookWhat to do:

1. Tie a book to a thread such that some portion of the thread hangsfrom below the book.

2. Hang this arrangement from a support.

3. Pull the thread with a jerk from the lower end.

4. The lower portion of the thread below the book breaks. Why?

5. Now tie the thread back.

6. Again pull the thread from below but pull it slowly this time.

7. The thread above the book breaks from the upper support. Why?

Why does it happen: A sudden jerk on the thread from below increases thetension in the thread locally. The stress produced by the jerk exceeds thebreaking limit and the thread breaks from below. The book and the threadabove the book are not affected because the time duration of the jerk isso small that before the disturbance produced due to it reaches the upperend of thread, the lower thread breaks.

When the pull is gradual there is enough time for the disturbance totravel the entire length of the thread. Due to the weight of the book thethread above the book now experiences a greater tension as compared to

the thread below the book. Hence the thread breaks from its upper end.Similarly when we hold a mango growing on a tree and give it a jerk wemanage to increase the tension locally to the twig with which it is attachedto the main branch. Hence we can enjoy a mango!


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Demonstration 14

A Magical Coin

jfaIntroduction: In most of the popular sciencebooks studied by the students we come acrossa concept of inertia of rest in relation to theNewton’s first law of motion. A body at restmaintains its state of rest if the net force on itis zero. This unwillingness to change its state of rest is described as the inertia of rest.

To demonstrate the inertia of rest there are many experiments whichare done. But do these experiments really achieve the condition in whicha body can exhibit inertia of rest?

We attempt to analyze it by this demonstration.What do you need: A match box and a coinWhat to do:

1. Insert the coin between the match box case and its drawer till it isnot visible.

2. Tap the match box with your finger sharply.

3. See the coin emerging out of the box.

Point of discussion: It seems as if the sharp taps given to the matchbox are making it go down. The coin on the other hand seems to be atrest, as instead of going down with the match box, it emerges up.

So is the coin really at rest? Is the force experienced by the coin zero? Why does it happen: When the coin is inserted vertically in the match

box drawer, its weight acts downward. This is balanced by the force of friction on it acting upward. The force of friction on the coin is due to itscontact with the inner surface of the match box drawer. So the coin is inequilibrium.

On tapping, the match box gets a large impulse which accelerates itdownwards. The coin in contact with the drawer now experiences a forceof friction downwards. The acceleration of the match box is large, so theforce of friction on the coin tries to attain this acceleration and shoots upto its maximum possible value. But the maximum force of friction onlymanages to move the coin down with acceleration much smaller than thematch box. So relative to the match box, the coin moves a much smallerdistance downwards and hence it emerges out of the match box.

If the force applied on the match box is small, the coin will not emergefrom the match box. In this case the force of friction on the coin will besufficient to produce acceleration equal to the match box. So both of themwill now move the same distance down together.


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Demonstration 15

Lift a Weight by Moving another Weight in a Circle

nbaPass a thread through the both side open plas-tic body of a used pen. Tie two unequal massesm and M on the two sides of the string. Holdthe plastic body in vertical position in your handwith the heavier mass M hanging and the lightermass m resting at the top of the plastic body.Give motion to the masses by rotating yourhand little bit so that the upper mass is set in nearly circular motion.As soon as it acquires sufficient speed it will pull the hanging body up. If you speed up the rotating body the heavier hanging mass can move rightup to the plastic body.

You can adjust the speed of the rotating body by manipulating the forceprovided by your hand. By properly adjusting this force, you can keep thehanging body fixed at a desired height.

You can discuss this phenomenon of the hanging mass going up in anumber of ways. The tension in the string, which provides the centripetalforce, should be mv2/r. But this tension should also be Mg, the weight of the hanging body if it keeps in equilibrium. Thus mv2/r = M g. Now whenyou increase the speed of the rotating mass m by adjusting the force fromyour hand, the tension mv2/r is increased and hence the mass M movesup with acceleration.

You can also show conservation of angular momentum, L = mw2r, bydemonstrating increase of ω when r is reduced (by pulling the thread).

References



http://localhost/var/www/apps/conversion/dbAb/a/ba/nba.padhttp://www.vigyanprasar.gov.in/activity_based_science/Expm5.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm5.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.vigyanprasar.gov.in/activity_based_science/Expm5.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm5.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/nba.pad


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Demonstration 16

Key-bottle experiment

ifaIntroduction: This is an eye catching demonstration which gives an insightinto many concepts of physics like friction, connected motion, vertical circle

What do you need: 200 ml plastic bottle filled with water, key, 1msturdy thread, a used pen

What to do:

1. Tie the plastic bottle to one end of the thread and tie a small key tothe other end of the thread.

2. Pass the thread over the body of the pen which acts as a pulley.3. Now hold the pen in one hand and the key tied to the thread in your

other hand such that it makes an angle of around 45 degree with thehorizontal.

4. Keep the length of the thread on the side of the bottle hanging overthe pulley much smaller than the length of portion of the thread tiedto the key over the other side of pulley

5. Now release the key.

6. The audience hold their breath as they expect the heavier bottle toslide and crash to the ground

7. But amazingly the bottles downward journey is halted as the threadtied to the key curls many times around the pen and stops any furthermovement.

Why does it happen: When we release the key, the bottle being heavierstarts accelerating down and the key tied to the thread falls down likea pendulum released from its extreme position. But as it falls down the

length of the thread goes on decreasing and its velocity goes on increasing.By the time the key reaches the bottom of the circle it acquires the velocityrequired for completing a vertical circle. So the thread loops around thepen. The bottle still accelerates down so the thread keeps looping aroundthe pen till it stops the motion of the bottle.

As number of loops increase, the friction on the thread increases. Theincrease in the contact area of the thread with the pen increases the normalreaction of the pen on the thread which in turn causes the friction toincrease.

To be merged with Get Going Mug on page 9.


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Demonstration 17

Spring Potential Energy

gbaTake a toy car with spring mechanism. Makea mark on a uniform floor with a chalk. Windthe key of the car through half a turn, and placethe toy at the mark on the floor. Make anotherchalk mark at the point where the car stops.Measure the distance x between the two marks.This is the distance moved by the car. Rub outthe second mark.

Now, wind the key through a full turn andplace it at the first mark. Measure the distance the car moves beforestopping. Repeat the experiment for one and a half turns of the key andtwo turns of the key. Measure the value of x in each case.

The greater the number of turns, the larger is the distance travelled bythe car. This is because when the spring is compressed more, it stores moreenergy. The distance x is roughly proportional to the energy stored in thespring. Try to get the relation between the energy stored and the numberof turns of the key.

References



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Demonstration 18

Calibrating a Non-Linear Spring

leaObjective: To calibrate a spring and get the mass of a given object.

Apparatus: A spring, A hanger of 100g and 4 separate weights of 100geach, Meter Scale fixed with a nail for hanging the spring , clamp, Objectof unknown mass, Graph paper, 6” plastic scale

Instructions: You have to clamp the given meter scale vertically with thenail /rod on the upper side. It is a nonlinear spring and hence you cannothave a unique spring constant. To measure the mass of the given object youmust first calibrate the spring with the given standard masses, that is toknow the extension of the spring for each of these masses. You should drawa calibration graph with the standard masses and then obtain the mass of the given object from the extension corresponding to it. Actual extensionis not needed for this calibration. Do your experiments as accurately onyou can and mentions the possible errors and your efforts to reduce it.


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Demonstration 19

Linear Momentum of the Ball

dbaTake two identical plastic balls. Make a hole inone of them and fill it with sand. Seal the holewith tape. Now you have two balls of differentmasses. Make a pile of sand on the floor anddrop the lighter ball on it from a height. Theball will penetrate into the send to some depth.Make the pile again and drop the heavier ball onit from the same height. This ball will penetratedeeper into the sand. Dropping from the sameheight ensures that balls strike the sand with thesame velocity. So, increasing the mass increases the depth of penetrationwhen the velocity remains the same.

Now drop one of the balls from different heights on the pile. Droppingfrom a larger height means the ball strikes the pile with larger velocity. So,increasing the velocity increases the depth of penetration when the massremains the same.

If you drop the lighter ball from a greater height and the heavier ball

from a lower height, it may happen that the depths of penetration becomethe same. This will happen when the product mv is the same.

References



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Demonstration 20

Why Does it Goes Up?

mbaBodies put on an inclined plane come down theplane. This can be understood in terms of po-tential energy. By coming down, the gravita-tional potential energy decreases. A system un-der given conservative forces moves in such away that the potential energy decreases. Thisdemonstration emphasizes this principle in a dramatic way.

Join two plastic funnels at the rim with the help of an adhesive. Thismakes a double-cone. Arrange to make a rail by two spokes in such a waythat the height of the rail as well as the separation between the spokesgradually increases. You can take two pieces of thermocol and push thespokes properly in them to make the structure. The plane of the spokesbecomes an inclined plane. You will have to adjust the geometry by trialfor the demo to work. The height of the rail increases from A to B .

Place a cylindrical object like a pencil near the top of the rail and seethat it comes down as expected. Now place the double cone near the topand it won’t come down. Place it near the bottom. It goes up and settlesnear the top of the rail.

Because of the geometry, as the double cone goes from A to B , suppos-edly up the rail, more and more portion of the middle bulge goes betweenthe spokes and the cone actually dips. You can measure the height of thestraight tube part of the funnel above the table when the double-cone isnear the bottom of the rail and when it is near the top of the rail. It isless in the later case showing that the double cone is actually going downwhile it seems to go up.

Quantification: Ask students to measure change in potential energy intwo cases. Need to give a scale and balance.

References


[2] Arvind Gupta Video: https://www.youtube.com/watch?v=EXOs38T-HV4


http://localhost/var/www/apps/conversion/dbAb/a/ba/mba.padhttp://www.vigyanprasar.gov.in/activity_based_science/Expm4.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm4.htmhttps://www.youtube.com/watch?v=EXOs38T-HV4https://www.youtube.com/watch?v=EXOs38T-HV4http://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.youtube.com/watch?v=EXOs38T-HV4https://www.youtube.com/watch?v=EXOs38T-HV4http://www.vigyanprasar.gov.in/activity_based_science/Expm4.htmhttp://www.vigyanprasar.gov.in/activity_based_science/Expm4.htmhttp://localhost/var/www/apps/conversion/dbAb/a/ba/mba.pad


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Demonstration 21

Counter-intutive Centre of Mass with Bottle

tcaReferences

[1] Arvind Gupta Video: http://youtu.be/qJQPjFevfws


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Demonstration 22

Balancing the Scale on Fingers

mdaThis demonstrate the concept of centre of mass.Support a meter stick horizontally with two fin-gers (of two hands). Slide your fingers in andthey will both meet at the center of mass. Toexplain this, you need to understand friction and equilibrium. In staticequilibrium, net force and net torque on the scale is zero.

Give scale to a volunteer. Hold the scale horizontal by placing finger of one hand below one end of metre scale and finger of another hand belowthe mid point of scale. Ask him to move the finger at the end of the scale.It is easy do so. Now ask him to move the finger at the mid-point. He isunable to do so. Why?

References

[1] Source: https://www.lhup.edu/~dsimanek/scenario/demos.htm


http://localhost/var/www/apps/conversion/dbAb/a/da/mda.padhttps://www.lhup.edu/~dsimanek/scenario/demos.htmhttps://www.lhup.edu/~dsimanek/scenario/demos.htmhttps://www.lhup.edu/~dsimanek/scenario/demos.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.lhup.edu/~dsimanek/scenario/demos.htmhttp://localhost/var/www/apps/conversion/dbAb/a/da/mda.pad


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Demonstration 23

To find Centre of Mass of a Rectangular Shape

meaObjective: To find the Center of Mass (C.M.) of the given rectangular plate.

Apparatus: Clamp with nail fixed, Plumb Line, 30 cm Plastic Scale, Rect-angular Plate

Instructions: You are given a rectangular cardboard plate and are supposedto find out its Center of Mass. You can think of your method with the givenapparatus, but one way is to hang the board from the fixed nail and with thehelp of the plumb line you can locate vertical lines through the holes. If youdecide for that, mark two or three points on the surface, along the plumbline for each hole. Dont draw lines till you finish with all the holes.Only atthe end, put the plate on the table and draw all the lines using scale andpencil. Write your name and roll number on the sheet before submittingto the evaluators.


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Demonstration 24

To Find the Coefficient of Restitution

reaObjective: To find the coefficient of restitution in an inelastic collision.Apparatus: An wooden block with a trench, a sun mica board, a caromstriker, powder, scale, pencil, eraser.Introduction: When an object hits a wall obliquely, it reflects. If frictionduring the collision can be neglected, the parallel component of velocityremains unchanged but perpendicular component changes. If the collisionis elastic, the net speed remains the same and hence the perpendicularcomponent also remains the same. As a result, angle of incidence is equalto angle of reflection. However, if the collision is partially inelastic theperpendicular component decreases and the angle of reflection will exceedangle of incidence. The coefficient of restitution is obtained by e = tan θ1tan θ2 ,where θ1 and θ2 are the angles of incidence and reflection. In the experimentyou will use this equation.Experiment: Look at the wooden block and the sunmica board. The boardcan be fitted to the block just by inserting it in the trench. You can keepthe whole thing on a horizontal surface, the board making an inclined planeof a small angle. This inclination has no role in the experiment.

Half the wall of the block is wood and the other half is foam. By justflipping the block you get the other kind of wall on the top. Sprinkle somepowder on the board very gently, so that a thin layer is formed. Put strikeron the board at some distance from the wall and flick it so as to hit thewall obliquely. The angle should be large enough to give you significantdifference between the angles of incidence and reflection if any. As thestriker moves through the powder, it makes a trail which you can see. Verycarefully draw pencil lines to mark the incident and reflected directions of the center of the striker. Draw perpendicular to the wall that goes through

the point of intersection of these two directions.Now you can get e from the equation. Repeat at least 3 times with

wooden surface and 3 times with foam surface.Hazards: No hazardsAcknowledgement: Designed by Shiksha Sopan.


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Demonstration 25

It is not Easy to Do Simple Movements!

ndaSit on chair with legs and backbone vertical. Tryto stand up without moving the upper portion of your body forward or lower portion of your bodybackward. Can be used to explain concepts likecentre of mass, torque etc.

Variant: Turn your right side to the wall.Turn your right foot and cheek against the wall.

Now try to lift your left foot off the floor.

Both of these stunts require you to shift yourcenter of gravity away from the support base.The body maintains balance with little adjust-ments so automatic that we never think about them.

References

[1] Source: http://www.arvindguptatoys.com/arvindgupta/betyoucant.pdf


http://localhost/var/www/apps/conversion/dbAb/a/da/nda.padhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://localhost/var/www/apps/conversion/dbAb/a/da/nda.pad


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Demonstration 26

Win a 100 Rs Note

odaStand with your heels against a wall and yourfeet together. Place a 100 Rs note on the floorabout a foot in front of your feet. Now, try topick up the 100 Rs note without moving yourfeet or bending your knees. You cant pick it up.This demo explains concept like centre of mass,static equilibrium, torque etc.

When you stand straight against the wall, your center of gravity is overyour feet (base) as it should be. When you bend forward, you move yourcenter of gravity forward. In order to keep your balance, you must moveyour feet forward too. This maintains the base under the center of gravityneeded for stability. If you persist in trying to pick it up, you’ll fall flat onyour face!

References

[1] Source: http://www.arvindguptatoys.com/arvindgupta/

betyoucant.pdf


http://localhost/var/www/apps/conversion/dbAb/a/da/oda.padhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/[email protected]://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://www.arvindguptatoys.com/arvindgupta/betyoucant.pdfhttp://localhost/var/www/apps/conversion/dbAb/a/da/oda.pad


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Demonstration 27

Self Balancing Toy

pdaThis toy is in the form of question mark. It balances itself.


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Demonstration 28

Rolling and Kinetic Friction

qdaKeep a pen (cylinder) between your palms.When you move the palms, observe the trans-lation motion of the pen and your hand. Thisdemo can be used to show rolling without slip-ping, translation and rotational motion etc.


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Demonstration 29

Gyroscope from cycle wheel

heaIntroduction: It is a common experience thata bicycle can be parked only when we supportit with a stand otherwise it will fall down. Butthe same bicycle when moving on the road canbe balanced very well on its two wheels. Wheelsof a moving bicycle have a very large spin angu-lar momentum which helps in maintaining the

balance of the bicycle. This is the basic prin-ciple of a gyroscope. In this demonstration wewill see how a spinning cycle wheel is affectedby external torque.

Equipments:A cycle wheel with an axle, rope

Procedure

1. Attach a rope to the axle of the cycle wheel.2. Hold the cycle wheel by the rope. See that the wheel topples down.3. Hold the cycle wheel from its axle and give it a spin in clockwise

direction.4. When the wheel acquires a large angular velocity, leave the axle and

hold the wheel by the rope attached to the axle.5. See that the wheel instead of toppling this time starts prcising around

the rope in the anticlockwise direction when seen from above.6. Now hold the cycle wheel from the axle, spin it in anticlockwise di-

rection, and again hold it with the rope but this time see that thewheel prciss in a clockwise direction around the rope.

7. When the wheel is held by the rope, (i) why does it topple when it is

not spinning and (ii) why does it start prcising when it is spinning?

Discussion: When we hold the cycle wheel by the rope attached to theaxle, the tension in the rope and the weight of cycle wheel acting throughthe centre of mass of the wheel cause a torque which topples the wheel. Aspinning wheel has a spin angular momentum L, whose direction is givenby the right hand thumb rule. If you spin it in clockwise direction, the spinangular momentum L is away from you and perpendicular to the plane of the wheel. If you spin it in anticlockwise direction, L is towards you. If

the angular velocity is large, L is also very large.Now, when a torque is applied by holding the rope, the torque acts in adirection perpendicular to L. This causes an additional very small angularmomentum dL in the direction of the torque. The net angular momentumis now the vector sum of L and dL which is no more perpendicular to theplane of the wheel but is slightly tilted towards the applied torque. This


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32 Demonstration 29. Gyroscope from cycle wheel

causes the angular momentum L to follow the torque and the wheel startsprcessing about the rope.

Reversing the direction of angular momentum L causes the wheel toprcess in an opposite sense.

Variant: This demo can be done with Toy Gyroscope on page 35.


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Demonstration 30

To study the theorem of perpendicular axes in Moment of Inertia

xeaObjective:To study the theorem of perpendicular axes in Moment of Inertia.Introduction: For planer bodies, the sum of the moments of inertia abouttwo axes, perpendicular to each other but in the plane of the body, equalsthe moment of inertia of the body about the axis through the same pointperpendicular to the plane. The moment of inertia of an object can befound by suspending it from a support and allowing it to oscillate aboutthe suspension. The time period happens to be proportional to the squareroot of the moment of inertia. T = k

√ I .

Apparatus: An wooden plate with two bolts fixed on the sides and one atthe center, a wire fixed with a nut, clamp-stand, stop watchInformation for the students: Suspend the plate by fixing the bolt in a nuton a side. Let the plate be suspended . Now twist the plate about thevertical axis and measure time period using stop watch. Make sufficientno. of readings to be sure of the value. This gives moment of inertia I x upto the proportionality constant.

Open the nut and screw it in the bolt on other side. Get the timeperiod of twist oscillations. From this find the moment of inertia I y up tothe proportionality constant.

Again open the nut and screw it in the bolt at the center of the plate.Get the time period of twist oscillations. From this find the moment of inertia I z up to the proportionality constant.

Find the value of I x+I y

I z.

Acknowledgement: Developed at SGM-IAPT Anveshika


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Demonstration 31

Paper Helicopter

ccaThe paper helicopter is very easy to make. Cutout a rectangular piece of paper approximately4 cm× 15 cm. Fold the paper (along length) inequal halves and then unfold it. Cut along thefold crease upto half of the length. Now, cutabout 1/3 through the paper laterally a littlebelow your first cut on both sides and fold these parts along length. Makefolds as shown in paper. Don’t forget to add a paper clip at the bottom.The helicopter rotates when you drop it from a height of 2 m or above. Whythe blades rotates? If you fold the blades in opposite direction then direc-tion of rotation changes! This simple toy can be used to explain conceptof centre of pressure, torque, angular momentum etc.

References

[1] Web Source: http://www.wikihow.com/Create-a-Paper-Helicopter


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Demonstration 32

Gyroscope Using Toy Motor

dcaThe equipment consists of a toy motor poweredby two AA batteries.Making: Take a toy motor. Take two CD andan alminium sheet of the size of CD. Place thealuminium sheet between two CD. Fix this as-sembly to the axle of motor. Paste/draw Net-won’s disc on outer CD. This equipment can beused for three concepts as discussed below.Newton Disc: When connected to battery, the motor start rotating andyou get a low cost Newton’s disc.Magnetic Brake: Bring a magnet close to the disc. The speed reduces. Youcan explain about eddy currents and magnetic brake. See also page 164.Gyroscope: Suspend entire assembly was from a thread which does notpass through centre of mass. When motor is switched on, the CD rotatesproviding angular momentum to the system. The torque due to weightabout centre of mass causes angular momentum (direction) to change andthe system precesses about vertical axis. Changing the polarity on battery

change direction of rotation. Physical law is τ = d L

dt . This set up seems tobe good for classroom demo as carrying bicycle wheel in classroom is littlebit cumbersome. See also page 31.


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Demonstration 33

Coupled Pendulum

kcaCoupled Pendulum to show energy transfer.Similar to what Masti Ji shown in KolkataSRP.


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Demonstration 34

SHM Phase and Phase Difference

feaIntroduction: An oscillating pendulum, a corkbobbing up and down in water or the periodicmotion of the mass attached to a spring have onething in common. They are all executing sim-ple harmonic motion (SHM). Simple harmonicmotion is a special type of oscillation. The con-cept of phase and phase difference associatedwith SHM is generally difficult to comprehend.In this demonstration this concept of phase andphase difference can be understood easily.Equipments:A stand, two pendulums made by attaching two similar plas-tic balls with two threadsProcedure:

1. Hang the two threads attached to the plastic balls to the stand tomake the two pendulums.

2. Make the length of the threads same.

3. Take both the balls to one extreme and release them together.4. Both the balls oscillate in a similar manner i.e. they have same timeperiod, reach the other extreme in the same time and are at sameposition at any instant of time.

5. We say that both are in the same phase and their phase difference iszero.

6. Now take one ball to one extreme and the other ball to the otherextreme and release them simultaneously.

7. See that the balls move opposite to one another at all times i.e. if one

moves right the other moves left. Also if one is at the right extreme,the other is at the left extreme.8. We say that both are in opposite phase and their phase difference is

π.9. Now make the length of one of the pendulums slightly less than the

other10. Again release both of them simultaneously from the extreme position.11. This time the two do not move together, one with the smaller length

reaches the other extreme earlier, so we say that they are not in phase.12. But the phase difference between them does not remain constant,

first it increases with time and becomes equal to , then the phasedifference starts decreasing and becomes equal to zero and again itincreases to and then goes to zero. This process repeats itself and iscalled beats.

Discussion: SHM is an oscillation in which a particle moving in a straight


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38 Demonstration 34. SHM Phase and Phase Difference

line experiences a force which directs it towards its mean position and themagnitude of the force is proportional to the displacement from the meanposition. It can be represented by a sine or cosine function. The argumentof the sine or cosine function is called the phase of the particle executing

SHM. Phase tells about the state of the particle at any instant.In the above case the SHM of the pendulums which are released from

their extreme position can be represented by the equations X 1 = A1 cos(ω1t+θ) and X 2 = A2 cos(ω2t + φ), where A1 and A2 are the amplitudes, θ andφ are the initial phases, ω1 and ω2 are the angular frequencies and thearguments (ω1t + θ), (ω2t + φ) are the phases of the two pendulums at anyinstant.

Since the frequency of the pendulum is dependent on its length, whenthe length of the threads is kept same ω1 = ω2. Now if the balls are released

together from1. Same extreme, initial phases θ = φ = 0 and phase difference = 02. Opposite extremes, θ = 0 and φ = π and phase difference = φ−θ = π.

Also the amplitudes A1 = A2.

When the length of the threads is different ω1 = ω2. Now if the ballsare released together initial phases θ = φ = 0 but the phase difference is(ω1t−ω2t) which changes with time and oscillates between the value 0 andπ causing beats.


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Demonstration 35

Resonance in pendulum by hand

geaIntroduction: Some times in a movie we seethat when an opera singer sings, the glass inher hand shatters. Also at times when we closethe door, the window panes in the room startrattling. The phenomenon governing the aboveevents is resonance. When the frequency of theopera singer (or closing door) matches with thefrequency of the glass (or window), resonance occurs. In this demonstrationwe show this phenomenon of resonance.Equipments:A pencil, a thread, a nutProcedure:

1. Tie a nut to one end of a thread.2. Wrap the other end of the thread on a pencil to make a simple pen-

dulum.3. Apply a small force on the pendulum to make it oscillate.4. Leave it free so that it starts oscillating with its natural frequency.

5. Now rotate the pencil in clockwise and anticlockwise direction peri-odically with your fingers.6. Do it very slowly(at frequency much less than natural frequency of

pendulum).7. See that the amplitude of the oscillations becomes very less.8. Again give a rotation to the pencil in a similar manner, but this time

do it very fast.(at frequency much more than the natural frequencyof pendulum)

9. The amplitude of oscillation is still very less.

10. Now rotate the pencil in such a manner that frequency of the peri-odic rotation given to the pencil matches with the frequency of thependulum. This will require some practice.

11. See that the amplitude of oscillation of the pendulum becomes verylarge.

Discussion: Every body oscillates with its natural frequency when it isleft free.This natural frequency depends on the shape, size and materialof the body. If the body is subjected to a periodic force the body startsoscillating with the frequency of this periodic force after some time. But

the amplitude of these oscillations is very small if the forced frequency isdifferent from the natural frequency. If the forced frequency happens tomatch with the natural frequency, the body gains a lot of energy and itsamplitude become very large. We call this the resonant frequency.


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Demonstration 36

To Study Torsional Oscillation of a Rectangular Body

oeaObjective:To study the torsional oscillation of a rectangular body suspendedby two non parallel threads.

Apparatus: Clamp, Suspension plate with nails fixed, Oscillating plate withhooks and threads fixed, Meter Scale, Stop Watch, Graph Paper

Instructions: Suspend the oscillating plate using the threads and the innerpair of nails on the suspension plate. The upper edges of the plate shouldbe horizontal.

Rotate the plate about the vertical bisector through a small angle andrelease. The plate should start oscillating.

Let the height of the nails over the upper edge of the plate be H andtime period of oscillation be T . You are suppose to find the relation betweenT and H . So measure T and H at appropriate length and draw a graphbetween T and H . From this, guess whether T ∝ H 2, T ∝ H or T ∝√

H .


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Demonstration 37

Why Balloons come Closer?

acaThe Bernoulli principle enables aircraft to fly.This experiment demonstrate Bernoulli’s prin-ciple in a simple way. Hang two balloons a fewinches apart. Blow air between them. Whathappens? Whether balloons come closer or goesfarther away? Why? You can also do this ex-periment by blowing air above a strip of paper.

Electrostatic Variant: Same setup can be used to show electrostaticattraction and repulsion between balloons when they are charged.


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Demonstration 38

Why the fluid does not comes out?

kdaUse the scissors to make a small hole on the sideof the water bottle, closer to the bottom.

The water starts coming out in a parabolicpath.

Fill the water bottle and put your finger overthe hole. Take your finger off the hole and letthe water bottle drop. What happened duringthe drop? Did the bottle leak?

When the cup is at rest, the force of gravitypulls downward upon the water. At the locationof the holes, there is nothing to balance gravity’s force and prevent waterfrom spilling out of the cup.

However, when the cup is in free fall, the water will not leak, making itseem as though the water is not experiencing the downward pull of gravity.It is merely falling to the ground at the same rate as its surroundings (thecup).

References

[1] Source: http://www.physicscentral.com/experiment/physicsathome/free-fall.cfm


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Demonstration 39

Suspending a Cup by a Balloon

rdaThis demo explains the concept of air pressureand Boyle’s law, P V = constant.

Blow up a balloon to less than half its poten-tial size and close off the opening. Then placethe mouth of a paper cup against the side of the balloon and hold it therewhile you blow up the balloon the rest of the way. You will find the cupbecomes “fastened” to the surface of the balloon and will actually hold on

fairly tightly until you force the cup to “let loose” of the balloon. Becauseof the curvature of the surface of the balloon, when it is not blown up allthe way, you place the mouth of the cup against its surface, and the balloonextends a small distance into the cup. Then, as you blow up the balloonfarther, its curvature becomes such that the volume of the air trappedinside the cup becomes larger, thus lowering the pressure inside the cup.The pressure inside the cup is now less than atmospheric pressure, and theatmosphere outside the cup “pushes the cup” onto the balloon.

References

[1] Source: https://www.physics.umn.edu/outreach/pforce/circus/airpressure.html


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Demonstration 40

Keep the Paper Dry in Water

sdaStuff a large handkerchief or some crumpled-newspaper into an empty glass or jar. Makesurethe handkerchief wont fall out when youturn theglass upside down.Then, fill a pot withwater. Holding the glass sothat its mouth isdown, put the glass deep into thepot of waterand hold it there. After a minute ortwo, pull the glass out of the water andremove thehandkerchief.

Water cannot fill the glass because the glass is already filled with air.The “empty” glass is full of air. So, air takes up space. Air is a gas. It hasno size or shape of its own butwill fill every space it can.

References

[1] Source: arvindguptatoys.com http://goo.gl/pqaj2C


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Demonstration 41

Push Water in a pair of Connected Syringes

tdaThis simple experiment is often taken as an ex-ample of Pascal’s law of transmission of Pressureor a demonstration of F = P A. However thispopular belief does not pass the test of deeperanalysis. Equipments needed are two syringesof different sizes connected by a small flexibleplastic tube. Some water is filled in one of thesyringes. The procedure is,

1. Suppose you have water in the bigger syringe and the piston of thesmaller syringe is staying against the end. Hold the bigger syringebetween the two fingers and a thumb. The thumb is on the circularbase of the piston while the fingers are on the two extrusions of thebarrel.

2. Push on the base by the thumb so that water goes from the biggersyringe to smaller one. Feel the amount of force.

3. Now water is in the smaller syringe. Holding the this syringe as usual

between two fingers and one thumb, push the water back to biggersyringe. Feel the force you have to apply.

4. Compare, in which case you had a apply a larger force.

As you are comparing forces in two different experiments (Step 2 and 3above), you should not use Pascal’s law which talks about increase in pres-sure everywhere in the liquid, but at the same instant. For the same reasonyou cannot equate pressure in two cases and make force proportional to thearea of the base. Then what is it?

References

[1] Source: Utsahi Physics Teachers Website http://goo.gl/4uFmTu


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Demonstration 42

Blow Air in a Long Air Bag

udaHere’s the challenge. How many breaths wouldit take to blow up a 2 meter (8 ft) long bag? De-pending on the size of the person, it may takeanywhere from 10 to 50 breaths of air. However,with a little practice and some scientific knowl-edge of air... you will be able to inflate the bagusing only one breath!


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Demonstration 43

To find the atmospheric pressure using a syringe and weights

seaObjective:To find the atmospheric pressure using a syringe and weights.Apparatus: A syringe with one end closed and very little air trapped in it.An identical extra syringe, Support system for keeping the syringe fixedin vertical position. A pan suspended from the lower end of the syringebarrel, known weights.Introduction: Suppose there is no air trapped in the syringe. When youput small amount of weight on the pan, the piston stays in its position.If you pull the piston down and release, it will be pushed up because theforce by the atmosphere is more than the weight put. But if the weight isequal to the force by the atmosphere, and you pull the piston little bit andrelease, the piston will stay wherever it is released. By measuring the innerarea of cross section of the syringe, you can get the atmospheric pressureby Atmospheric Pressure = Weight/Area.Experiment: Find the inner cross sectional area of the syringe. The weightrequired is definitely more than 1/2 kg.wt. So put 1/2 kg weight on thepan. Because of little air trapped the piston might come down little bit.From here pull the barrel little bit and release. If it goes up, you need toput more weight. Use smaller weights to find the position where the pistonstays wherever it is left. Try to get this situation correctly.

You might find that even if you make small variation in weight the pistonbehaves similarly and stays wherever it is left. This is due to friction. Findthe range of weights for which this situation occurs. Use the mean weightand calculate the atmospheric pressure.Questions: Due to the trapped air in the syringe do you expect the mea-sured atmospheric pressure to be more or less than the actual value? Canyou estimate this error in percentage.

Repeat at least 3 times to check for consistency.Hazards: Be careful to handle weights, they should not fall on your feet.Acknowledgement: Designed by Shiksha Sopan


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Demonstration 44

To measure the viscosity of water

veaObjective: To measure the viscosity of water.Introduction: Viscosity is counterpart of friction in liquids. When one layerof a liquid attempts to slip over the adjacent layer, there are forces by thelayers on each other to oppose the relative possible velocity. Essentially itopposes the velocity gradient in a liquid (or a gas). The effect is measuredby “Coefficient of Viscosity”. One standard way to get the viscosity of water is to let it flow through a narrow tube, and use Poiseuille equationdV

dt =

∆Pπr4

8ηL , where

dV

dt is the volume of water coming out of the tube, ∆P is the pressure difference across the tube, r is the radius of the tube, L isthe length of the tube and η is the coefficient of viscosity.Apparatus: A bottle with a plastic tube fixed at bottom, a syringe barrelclosed at its tip, a stop watch, a screw gauge, scale.Information for the students: The tube fixed in the bottle is the plasticsleeve over electric wires. We are giving you the wire removed from thesleeve. Assume that the inner diameter of the tube is equal to the diameterof the wire. Measure the diameter of the wire to get the radius of the tube

r. Measure the length L of the tube using a plastic scale. We have put amark near the neck of the bottle. Measure the height of this mark abovethe tube. You will be putting water in the bottle up to this height andthen ∆P will be equal to hρg.

Close the tube with one hand and pour water in the bottle up to themark. Release the tube. Water will start coming out from the tube. Startcollecting the water in the syringe and at

Documents

NANI Demo Booklet Ver 0.03 Jan 2015