Motion Introduction Section 0 Lecture 1 Slide 1 Lecture 3 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring

Motion

Introduction Section 0 Lecture 1 Slide 1

Lecture 3 Slide 1

INTRODUCTION TO Modern Physics PHYX 2710

Fall 2004

Physics of Technology—PHYS 1800

Spring 2009

Physics of Technology

PHYS 1800

Lecture 3

Motion

Motion


Lecture 3 Slide 2


Fall 2004


Spring 2009

PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet

*Homework Handout

Date Day Lecture Chapter Homework Due Jan 5 6 7 9

M T W F*

Class Admin: Intro.Physics Phenomena Problem solving and math Units, Scalars, Vectors, Speed and Velocity

1 App. B, C 1 2

-

Jan 12 14 16

M W F*

Acceleration Free Falling Objects Projectile Motion

2 3 3

1

Jan 19 21 23

M W F*

Martin Luther King Newton’s Laws Mass and Weight

No Class 4 4

2

Jan 26 28 29 30

M W Th F

Motion with Friction Review Test 1 Circular Motion

4 1-4 1-4 5

3

Feb 2 4 6

M W F*

Planetary Motion and Gravity Energy Harmonic Motion

5 6 6

4

Feb 9 11 13

M W F*

Momentum Impulse and Collisions Rotational Motion

7 7 8

5

Feb 16 17 18 19 20

M Tu W H F*

Presidents Day Angular Momentum (Virtual Monday) Review Test 2 Static Fluids, Pressure

No Class 8 5-8 5-8 9

-

Feb 23 25 27

M W F*

Flotation Fluids in Motion Temperature and Heat

9 9 10

6

Mar 2 4 6

M W F*

First Law of Thermodynamics Heat flow and Greenhouse Effect Climate Change

10 10 -

7

Mar 9-13 M-F Spring Break No Classes Mar 16 18 20

M W F*

Heat Engines Power and Refrigeration Electric Charge

11 11 12

8

Mar 23 25 26 27

M W H F*

Electric Fields and Electric Potential Review Test 3 Electric Circuits

12 13 9-12 13

-

Mar 30 Apr 1 3

M W F

Magnetic Force Review Electromagnets Motors and Generators

14 9-12 14

9

Apr 6 8 10

M W F*

Making Waves Sound Waves E-M Waves, Light and Color

15 15 16

10

Apr 13 15 17

M W F*

Mirrors and Reflections Refraction and Lenses Telescopes and Microscopes

17 17 17

11

Apr 20 22 24

M W F

Review Seeing Atoms The really BIG & the really small

1-17 18 (not on test) 21 (not on test)

No test week 12

May 1 F Final Exam: 09:30-11:20am

Motion


Lecture 3 Slide 3


Fall 2004


Spring 2009


PHYS 1800

Lecture 3

Motion

Units of Motion

Motion


Lecture 3 Slide 4


Fall 2004


Spring 2009

What Do We Need To Measure?

What is the minimum about things we need to know?

Where things are—a length, LWhen things are there—a time, T

How thing interact with gravity—a mass, MHow things interact with E&M—a charge, Q

How thing inter act with weak nuclear forceHow things interact with strong nuclear force

Motion


Lecture 3 Slide 5


Fall 2004


Spring 2009

Describing Motion

Position—where you are in space (L-meter)

Speed—how fast position is changing with time (LT-1 or m/s)

Acceleration—how fast speed is changing with time (LT-2 or m/s2)

Motion


Lecture 3 Slide 6


Fall 2004


Spring 2009

Units of Motion

Need a distance unit: m, cm, mm, km ft, in, mi

light years, furlongs

Need a time unit: sec, min, hr, day, yearms, ns, fsfortnights

Speed: A distance divided by time (DT-1)m/s, mi/hr, mm/yr, furlongs/fortnight

Acceleration: A distance divided by time squared (DT-2)A speed divided by time (DT-2)m/s2, mi/hr2, mm/yr2, furlongs/fortnight2

Motion


Lecture 3 Slide 7


Fall 2004


Spring 2009

Examples of Distance Units

Consider the lowly penny:

Value Notes on units Scientific notation 0.75 in “natural unit” 7.5 · 10-1 in 2 cm “natural” unit,

metric unit (note prefix) 2 cm

0.02 m SI unit, metric unit 2 · 10-2 m

0.00002 km metric unit (note prefix) 2 · 10-5 km

0.000012 mile 1.2 · 10-5 mile

0.01 fathom “odd” unit 1 · 10-2 fathom

0.000000000000000000002 light year “odd” unit 2 · 10-20 light year

0.000000002 angstrom “odd” unit 2 · 10-8 angstrom

Motion


Lecture 3 Slide 8


Fall 2004


Spring 2009

Dimensions of Motion

Distance: Dimensions; (L)

ScalarSymbol: dUnits: m, cm, km, in, ft, light years, furlongs

Time: Dimensions; (T)ScalarSymbol: tUnits: s (or sec), min, hr, day, year, ms, ns, fs, fortnights

Speed: A distance divided by timeDimensions; (LT-1) ScalarSymbol: sUnits: m/s, mi/hr, mm/yr, furlongs/fortnight

Acceleration: A distance divided by time squared A speed divided by time

Dimensions; (LT-2) ScalarSymbol: aUnits: m/s2, mi/hr2, mm/yr2, furlongs/fortnight2

Motion


Lecture 3 Slide 9


Fall 2004


Spring 2009


PHYS 1800

Lecture 3

Motion

Speed and Velocity

Motion


Lecture 3 Slide 10


Fall 2004


Spring 2009

What Is Speed?

Speed is how fast something is moving.– Speed is always some distance divided by some time.– The units of speed may be miles per hour, or meters

per second, or kilometers per hour, or inches per minute, etc.

Rate is one quantity divided by another quantity.– For example: gallons per minute, pesos per dollar,

points per game.– So average speed is the rate at which distance is

covered over time.

Motion


Lecture 3 Slide 11


Fall 2004


Spring 2009

Average speed is total distance divided by total time.

Instantaneous speed is the speed at that precise instant in time.– It is the rate at which distance is being covered at a

given instant in time.– It is found by calculating the average speed, over a

short enough time that the speed does not change much.

What Is Speed?

average speed = distance traveled

time of travel

Motion


Lecture 3 Slide 12


Fall 2004


Spring 2009

Average Speed

Kingman to Flagstaff:120 mi 2.4 hr

= 50 mphFlagstaff to Phoenix:140 mi 2.6 hr

= 54 mphTotal trip:120 mi + 140 mi

= 260 mi2.4 hr + 2.6 hr

= 5.0 hr260 mi 5.0 hr

= 52 mph

Motion


Lecture 3 Slide 13


Fall 2004


Spring 2009

Instantaneous Velocity

Instantaneous velocity is a vector quantity having:a size (magnitude) equal to the instantaneous speed at a given instant in time, and a direction equal to the direction of motion at that instant.

Motion


Lecture 3 Slide 14


Fall 2004


Spring 2009

Instantaneous Speed: a car traveling on a local highway

A steep slope indicates a rapid change in velocity (or speed), and thus a large acceleration. A horizontal line has zero slope and represents zero acceleration.

Motion


Lecture 3 Slide 15


Fall 2004


Spring 2009

What Does a Speedometer Measure?

The speedometer tells us how fast we are going at a given instant in time.

A speedometer measures instantaneous speed.

(In a moment, we’ll see why a speedometer doesn’t measure velocity.)

Motion


Lecture 3 Slide 16


Fall 2004


Spring 2009

Average speed?Instantaneous speed?

The speed limit indicates the maximum legal instantaneous speed.

To estimate the time a trip may take, you want to use average speed.

Which quantity is the highway patrol more interested in?

Motion


Lecture 3 Slide 17


Fall 2004


Spring 2009

Velocity

Velocity involves direction of motion as well as how fast the object is going.– Velocity is a vector quantity.– Vectors have both magnitude and direction.– Velocity has a magnitude (the speed) and also a direction

(which way the object is moving).

A change in velocity can be a change in the object’s speed or direction of motion.

A speedometer doesn’t indicate direction, so it indicates instantaneous speed but not velocity.

Motion


Lecture 3 Slide 18


Fall 2004


Spring 2009

YesNo

At position A, the car has the velocity indicated by the arrow (vector) v1.

At position B, the car has the velocity indicated by the arrow (vector) v2, with the same magnitude (speed) but a different direction.

A car goes around a curve at constant speed. Is the car’s velocity changing?

Motion


Lecture 3 Slide 19


Fall 2004


Spring 2009

Changing Velocity

A force is required to produce a change in either the magnitude (speed) or direction of velocity.

For the car to round the curve, friction between the wheels and the road exerts a force to change the car’s direction.

For a ball bouncing from a wall, the wall exerts a force on the ball, causing the ball to change direction.

Motion


Lecture 3 Slide 20


Fall 2004


Spring 2009

Why Velocity Is So Useful

Velocity is a vector and represents a bodies speed and direction.

• A force must act on a body to change its velocity (i.e. its speed, direction or both).

• The force causes the body to accelerate resulting in a change in its velocity.

• Acceleration is a vector and represents the rate of change of velocity with time.

Motion


Lecture 3 Slide 21


Fall 2004


Spring 2009


PHYS 1800

Lecture 3

Motion

Acceleration

Motion


Lecture 3 Slide 22


Fall 2004


Spring 2009

Acceleration

Acceleration is the rate at which velocity changes.– Our bodies don’t feel velocity, if the velocity is constant.– Our bodies feel acceleration.

• A car changing speed or direction.• An elevator speeding up or slowing down.

Acceleration can be either a change in the object’s speed or direction of motion.

t1VV

intervalTime velocityinChange

accelerationAverage 2

2smtVa

Motion


Lecture 3 Slide 23


Fall 2004


Spring 2009

Instantaneous Acceleration

Instantaneous acceleration is the acceleration at that precise instant in time.

It is the rate at which velocity is changing at a given instant in time.It is found by calculating the average speed, over a short enough time that the speed does not change much.

Motion


Lecture 3 Slide 24


Fall 2004


Spring 2009

Acceleration: Vector Direction

The direction of acceleration vector is given by the direction of the change in the velocity vector, .

- Acceleration vector in same direction as velocity when velocity is increasing.

- When the velocity is decreasing the change in is in the opposite direction to motion (ie. to slow car down)

- Acceleration vector is opposite direction when velocity is decreasing.- Deceleration is negative acceleration.

1V 2V

1V V+ =

2V

acar

accelerating

V

1V 2V

+ =car

decelerating

1V V 2V

a

V

Motion


Lecture 3 Slide 25


Fall 2004


Spring 2009

Example: Negative Acceleration

Jet preparing to land

Initial velocity V1=200 km/hr (=55.6 m/s)

Final velocity V2=120 km/hr (=33.3 m/s)

Time interval t=5 sec

sma2/

56.553.33

tVV

tV

a12

In general:- Whenever the velocity is changing we say the object is accelerating (positive or negative).

Acceleration:

runwaytowarda 46.4 sm 2/

Motion


Lecture 3 Slide 26


Fall 2004


Spring 2009

Return to car on a bendCar moved at a constant speed but its direction continuously

changed – thus its velocity was changing.

• But we now know that velocity changes are produced by an acceleration.

• Thus when the car rounds the bend at a constant speed it is accelerating!!• Direction of acceleration is given by direction.

Question: what is ?

Result: the vector acts towards the center of curvature of the bend!

V

V

AccelerationDirection

1V

2V

2V

1V

V+ =1V V

2V

V

Motion


Lecture 3 Slide 27


Fall 2004


Spring 2009

This is why the car does NOT change speed but you still feel a force on your body as you round the bend… (change in direction).

Thus the acceleration is also directed towards the center of curvature.

• Force is due to friction of tires on road enabling the car to change direction.

For a given speed the acceleration experienced (force) depends on the curvature of the bend.

Skiing - sudden turns create large accelerations & large associated forces!

Example:

sharp shallow

2V

2V 2V 1V1V

1V1V

2VLarge

t

Va Small

t

Va

V V

Motion


Lecture 3 Slide 28


Fall 2004


Spring 2009


PHYS 1800

Lecture 3

Motion

Graphing Motion

Motion


Lecture 3 Slide 29


Fall 2004


Spring 2009

Graphing Motion

Time

Dis

tanc

e

Time

Spe

ed

Time

Acc

eler

atio

n

Objectives: Understand what position, speed and acceleration are Learn to graph them versus time Develop some intuition for common situations

Consider: Standing still Constant speed (different magnitudes) Constant acceleration (different magnitudes) Constant deceleration (different magnitudes) Arbitrary motion

Motion


Lecture 3 Slide 30


Fall 2004


Spring 2009

Standing Still

Time

Dis

tanc

e

Time

Spe

ed

Time

Acc

eler

atio

n

Motion


Lecture 3 Slide 31


Fall 2004


Spring 2009

Constant Speed

Time

Dis

tanc

e

Time

Spe

ed

Time

Acc

eler

atio

n

Motion


Lecture 3 Slide 32


Fall 2004


Spring 2009

Constant Speeds

Time

Dis

tanc

e

Time

Spe

ed

Time

Acc

eler

atio

n

Motion


Lecture 3 Slide 33


Fall 2004


Spring 2009

Constant Acceleration

Time

Dis

tanc

e

Time

Spe

ed

Time

Acc

eler

atio

n

Motion


Lecture 3 Slide 39


Fall 2004


Spring 2009


PHYS 1800

Lecture 3

Motion

Vectors: Velocity and Acceleration

Motion


Lecture 3 Slide 40


Fall 2004


Spring 2009

Scalars and VectorsScalar: Measure of quantity or size

Sometimes called “magnitude”.Examples: Length, volume, mass, temperature, speed…

Vectors: Many measurements in physics require a knowledge of the magnitude and direction of quantity. These are termed vector quantities.Examples: Velocity, acceleration, force, electric field…

Direction is an essential feature of a vector quantity.Example: Flying at 1000 km/hr due North is quite different to the same speed due East!

Vectors require 2 pieces of information MAGNITUDE and DIRECTION.

Motion


Lecture 3 Slide 44


Fall 2004


Spring 2009


Next Lab/Demo: Free Fall

Tuesday 1:30-2:45 ESLC 53

Ch 2

Next Class: Wednesday 10:30-11:20

BUS 318 roomReview Ch 3

Documents

Motion Introduction Section 0 Lecture 1 Slide 1 Lecture 3 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring