Velocity

• Velocity is speed with a specified direction

• Velocity is a vector quantity

Using Vectors

• Bob walks 10 m East, stops for a while, then continues 7.5 m in the same direction. Where is he then? (What is the result of his motion?)

• Sue travels 5 miles North, turns around and travels 4 miles South. Where is she then? (What is the result of her motion?)

Using Vectors

• Karen walks 15 meters due East and then 30 meters due North. What did Karen really accomplish? What is the result of her motion?

• Pythagorean Theorem(Hyp)2 = (a)2 + (b)2

• Can use vectors to combine velocities to find resultant velocity Treadmill; examples in text

Acceleration

• An acceleration is a change in velocity.

in time change

yin velocit change a on Accelerati

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Acceleration

• Taylor is driving to work with a speed of 45 mph when she spies a traffic light. Upon noting the traffic light, Taylor removes her foot from the gas pedal. Ten seconds later, she was traveling with a speed of 5 mph. What was Taylor’s average acceleration as she came to a stop?

Acceleration ?

A

B

C

Acceleration

• If a car initially traveling (on ice) with a constant speed of 5 m/s experiences a constant acceleration of 4.5 m/s2, how fast would this car be going after 5 s?

• Would this car travel 138 m during the 5 s?

Acceleration

• An object with a velocity of 2 m/s experiences an acceleration of 3 m/s2 for 6s and then experiences an acceleration of 1 m/s2 for 4s. Does this object slow down during the last 4 s? (Note the velocity and accelerations are all in the same (+) direction.)

Acceleration1s

3m/s

1s

3m/s

1s

3m/s

1s

3m/s

1s

3m/s

1s

1m/s

1s

1m/s

1s

1m/s

1s

1m/s

1s

3m/s

Time elapsed

Speed Gained

2m/s 8m/s11m/s

14m/s17m/s

20m/s21m/s

22m/s23m/s

24m/s5m/s

Speed after time has elapsed

Many of us tend to think changes in acceleration mean the same kind of

changes in speed – BE CAREFUL – speed and acceleration are NOT the same!