Motion - Principle of Physics - Lecture Slides, Slides of Physics

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How can we describe the various motions in this situation?

Describing Motion

I.^

SpeedA.^

70 miles per hour1)^

In 1 hour, we would travel 70 miles 2)^

Speed has a number (70) and a unit (miles per hour) 3)^

Miles per hour = miles/hour = mph = miles

^

hours (distance/time)

B.^

Average Speed

= distance traveled divided by time of travel

1) 2)^

Average speed is a

rate

C.^

Converting units of speed: always distance/time1)^

Common Speeds

d^ t s

speed

 

^

distancetime

centsdollar

or

runsgame

or

milesgal

or

x^ y

m/h

Km/h

m/s

D.

Instantaneous Speed1)^

A Speedometer measures instantaneous speed 2)^

When you use different “speeds”a)^

Instantaneous speed tells you about the moment b)^

Average speed tells you how long the trip will take

3)^

Definition of Instantaneous Speed

= rate for a given instant = average

speed for a short time period where the speed changes little 4)^

Animation

II.

VelocityA.^

Velocity = speed in a defined direction1)^

20 mph = speed 2)^

20 mph due North = velocity

B.^

Changes in Velocity1)^

Car on a curve: speed stays the same, velocity is always changing2)^

Any change in speed

or

direction

is a change in velocity C.

Instantaneous Velocity

= average velocity for a short time period where the

velocity changes little

5)^

Vectors are represented by arrows (Velocity is always blue in the book)

B.^

Math with vectors: Appendix C1)^

Specifying magnitude and direction on a graph

2)^

Vector Components

= any 2 or more vectors that add up to the original

vector (usually components on the x and y axes are used)

5)^

More Examples