Forces and

Motion

Section1.2: Speed measures how fast position changes.

Here’s to Speed….

• http://www.youtube.com/watch?v=rw4eE8RMosQ

Vocabulary Word

• ______________ is the change of position over time.

Motion

Vocabulary Word

• ____________ is a measure of how fast something moves or the distance it moves in a given amount of time.

speed

00:00

00:0000:0100:02

00:0100:02

8 meters0 m

4 meters

How far will each skater travel in five seconds?

Calculating SpeedS = d

tS = speed

d = distance

t = time

A racer completes a 100-meter course in 20 seconds. What is his speed?

What do you know?Distance = 100 m

Time = 20 s

What do you want to find out? speed

Substitute into the formula: S = 100 m

20 s

Calculate: S = 5 m/s

A baseball travels 200 m in 25 s. What is its speed?

S = distance

time

S = 200 m

25 sS = 8 m/s

Practice Problem # 1

This bunny can travel 100 meters in 50 seconds. What is his speed?

S = 100 m

50 s

S = 2 m/s

Practice Problem #2

Vocabulary Word

• ___________ is a speed in a specific direction.Velocity

If two scooters are moving at the same speed but in opposite directions, is

their velocity the same?

5 m/s east5 m/s west

NO! Since they have different directions they have different velocities!

Green arrows show velocity. A longer arrow indicates a faster speed than does a shorter arrow. The direction of the arrow

indicates the direction of motion.

Vocabulary Word

• A _______________ is a quantity that has both size and direction.

vector

Your dog Sam often runs away from home. You know that he averages 2 kilometers per hour on these adventures. Is that enough information to

determine this location when he has been gone for 20 minutes?NO

A neighbor calls to tell you that she saw Sam making a beeline north. Now do you have enough

information to determine his location?

YES – only if he hasn’t changed direction since then.

VECTOR

• http://www.youtube.com/watch?v=A05n32Bl0aY