Lesson 4- Scientific Investigations

7/31/2019 Lesson 4- Scientific Investigations

1/14

LESSON 4 -SCIENTIFICINVESTIGATIONS

When physicists observe aparticular physical phenomenonthey will as questions as to howor why it happens . A hypothesiswill be put forth and experimentsor scientific investigations will becarried out to prove or disprovethe hypothesis. If the experimentsbear out the hypothesis, thehypothesis may come to regardedas theory or law of nature. If thedont the hypothesis will be

rejected or modified.In any experiment , the report onthe experiment will be based onthese guidelines and follows asequence as shown in thefollowing flow chart:

Inference

Early assessment that iscarried out to answer thequestions raised.

The inference should be writtenas :

MVdepends on RV.

OrRVinfluences MV

Hypothesis

A general statement about therelationship between amanipulated variable and aresponding variable.

The hypothesis should be written as :

The greater the MV, the greater theRV.

OrThe bigger the MV, the smaller theRV

Manipulated variable

The quantity whose values wedeliberately choose to change ora primary variable which causesother secondary variable tochange.

Responding variable

The quantity whose value dependon the manipulated variable or asecondary variablewhich changes in response to thechange in the manipulatedvariable.

Fixed variable

The quantity whose value is keptconstant throughout theexperiment.

Aim

A statement to show theinvestigation of the variablesinvolve.

21


2/14

The aim of the experiment shouldbe written as:To investigate the relationshipbetween ..and

Apparatus

List the apparatus and materials usedso that at

least a set of data for manipulatedand responding

variables can be determined.

State the arrangement of theapparatus that can

function by drawing a labelingdiagram .

Procedure

State the method of controlling themanipulated variablesState the method of measuring theresponding variablesRepeat the experiments at least fourtimes.

Tabulating the data

Record the data in the following table

Manipulatedvariable

Respondingvariable

Analyzing the data

Plot a graph of ( Responding variable)against(Manipulated variable)

How to tabulate the data ?

The table must be neatly drawn andthe data arranged in either and rows.

The names and symbols of themanipulated and respondingvariables must be written togetherwith the units.

For example,

Velocity, v/ s

Time , t /

s

Volume , V /m3

Pressure , P /Pa

The data shown in the table must be

consistent in the number of decimalplaces in accordance with therespective measuring instruments.For example,

Length, l /cm

Time , t /s

0 12.82 25.64 39.46 52.28 75.0

If the data too small or too big usethe standard form number.For exampleTemperature

/oC10 20 30 40 50

Density, /

kg m-3

x 104

9.7

8.5

7.3

6.6

5.1

How to plot the graph ?

The title of the graph must be shown.The axes of the graph must belabeled with the unit used.For example:

22


3/14

The scale chosen must be easy to useand is even scale.Even scales such 1:1 , 1:2 , 1:5 ,1:10 ,1:100 are proffered in plottinga graph.Odd scales such as 1:3 , 1:4 , 1:6 , 1:7 , 1: 30should be avoided in plotting a graph.

Make sure the area covered by the

plotted points must not be less than50% of the area of the graph paper.

For example:

The scale on the axes must beuniform and clearly marked withvalue.For example:

All the points are marked with a

symbol such as a cross or circle andthe centre of the cross mustaccurately positioned.

The best straight line or the bestcurve graph must be drawn.

The best straight line or the bestcurve graph is the line that passesthrough most of the points plottedsuch that it is balanced by thenumber of points above and belowthe line. The line also must smooth.

It is not advisable to plot graph byjoining point to point because thegraph obtained is not smooth.

How to analyze the data ?

(a) Determine the relationshipbetween two variables.Example :

y is directly proportional to x.

or y xor y = kx k = constantor y = mx m = gradientor y1 = y2

x1 x2

23


4/14

y increases linearly with xor y = mx + c

m = gradientc = intercept on axis-y

y decreases linearly with xor y = -mx + c

m = gradientc = intercept on axis-y

y is inversely proportional to x

or y 1x

or y = kx

k = constant

or y1

x1

= y2

x2

(b) Determine the gradient of thegraph

Example

Draw a sufficiently large triangleto calculate the gradient of thegraph.State value of the gradient withcorrect unit.

The gradient of the graph ism = y2 - y1

x2 - x1= QR

QR

(c) Determine the certain valuesfrom the graph.

Certain important values can beobtained from the graph plotted

by drawing a horizontal line or byextrapolating the graph.

(d) State the precautions should betaken

For example:The circuit connections must be

takenOff the switch when taking thereading of the meters.Make sure the amplitude ofoscillation is small.

24


5/14

1 Which of the following is the bestway to tabulate the data ?

A Voltage,V

0 5 10 15 20

Current,I

0 1.7 2.5 3.4 4.2

B Time,t /s

2.6 4.3 6 8.6 10

Density,

2000

5000

8000

11000

14000

C Length /m

2.5 3.3 4.6 5.8 6.9

Period,T/ s

10.5

15.3

19.8

27.9 36.0

D Objectdistance,u / cm

5.1 8.7 11.6

16.5 18.6

Imagedistance,v / cm

2.3 5 6.9 9 11.6

2 Which of the following scales isthe most suitable to plot a

graph?

A 1 cm : 3 unit B 1 cm : 5unit

C 1 cm : 6 unit D 1 cm :8.8 unit

3 Which of the following is the bestgraph ?

25

TUTORIA


6/14

4 Which of the following graphsshow that y increases linearlywith x?

5 Hookes law states that appliedforce Fis directly proportional tothe extensionxof spring if itselastic limit is not exceeded.Which of the following graphsshows the Hookes Law?

6 The acceleration, a of an object

is inversely proportional to themass, m of the object underconstant force.

Which of the following graphsdescribes the relationshipbetween a and m .

7 An experiment is carried out tofind the relationship between

mass and acceleration of a trolleyon a wooden runway.

The experiment is repeated byadding the number of trolleys.

The responding variable in thisexperiment is

A the length of the woodenrunway.

B accelerationC mass

8 In a simple pendulum experiment,the length of the pendulum andtime for 20 oscillations arerecorded.

The length of the pendulum is a

A manipulated variableB responding variableC fixed variable

9 Based on the graph above, what

is the gradient of the graph?

A - 1.5 B - 0.7C 0.7 D 1.0E 1.5

26


7/14


8/14


9/14

29


10/14

(a) Based on the aim and theprocedure of the experimentstate the:

(i) manipulated variable

________________________________

(ii) responding variable

_________________________________

(iii) constant variable

________________________________

(b) Measure the length of thespring in Figure 2.

lo = ___________________

Measure the lengths l of thespring in Figure 3 , Figure 4 ,Figure 5 , Figure 6 and Figure7 when different load areused.

In each case, calculate thechange in length,y, of thespring where;

y= ( lo l )Tabulate your results for m ,landyin the space below.

(c) On the graph paper , plot agraph ofyagainst m.

(d) Based on your graph, state therelationship betweenyand

m .

_________________________________

_________________________________

30


11/14

31


12/14

32

20 40 60 800

l/cm

1

2

3

4

5

T2

/ s2

Graph T2 against l

100

l / cm


13/14

20 A student carries out anexperiment to investigate the

relationship between the lengthof a simple oscillatingpendulum ,l ,with its period, T.

The experiment is repeatedusing different lengths, l, andtheir corresponding periods, T,are recorded. A graph ofT2

against l, is then plotted asshown above.

(a) Based on the graph,(i) State the relationship

between T2

with l.

..

..(ii) Calculate period, T, when

the lengthl = 45 cm.(Show your working)

l

(iii) Calculate the gradient ofthe graph.

(b) Using the value of thegradient obtained from (a)(iii)and the equation,

T = 42 Lg

calculate the acceleration due

togravity , g.

(c) State one precaution for thisexperiment.

21 The graph above representsgraph W against V , where Wand V are the distances on a

wooden rod.

(a) Based on the graph state the:

(i) manipulated variable

________________________________

(ii) responding variable

_________________________________

33


14/14

(b) Calculate the gradient of thegraph.

(c) Determine the intercept on(i) axis- W

....................................................

(ii) axis-V

.....................................................

(d) State the equation of the line

...............................................................

22 Azmi has a pendulum clock asshown in the diagram below.

Every day it was observed thatthe clock was slow about 2minutes.Pak Ali raised the position of thebob to correct the clock.Based on the observations:(a) State one suitable inference

that can bemade.

(b) State one appropriate

hypothesis for aninvestigation.

(c) With the use of apparatussuch as pendulum bob , stringand other apparatus, describean experimental frameworkto test your hypothesis.

In your description, stateclearly the following:(i) Aim of the experiment(ii) Variables in theexperiment(iii) List of apparatus andmaterials(iv) Arrangement of theapparatus(v) The procedure of the

experiment which includethe method of controlling

the manipulated variableand the method ofmeasuring the respondingvariable

(vi) Way you would tabulatethe data

(vii)Way you would analysisthe data

34

Documents

Lesson 4- Scientific Investigations