1. Accelerated Motion

2. is changing either the speed or direction, or both, of motion. Acceleration is the rate of change of velocity, in other words, how fast velocity is changing.

3. Acceleration Formula a =  v = v f - v i  t t f - t i Acceleration is a vector quantity and therefore must always be either positive or negative to indicate direction.

4. Example Problem #1 a =  v = v f - v i  t The cheetah can reach a speed of 19 m/s in 2.0 s from a standing start. What was the cheetah’s acceleration? (Assume the cheetah was moving to the right.) = + 19 - 0 2.0 = + 9.5 m/s 2

5. Example Problem #2 a =  v = v f - v i  t A car slows down from 15 m/s to 8 m/s in 3.5 s. What is its acceleration. (Assume the car is moving to the right.) = + 8 - + 15 3.5 = - 2 m/s 2

6. Positive vs. Negative A positive acceleration can mean –an increase in velocity, or –a decrease in velocity in the negative direction (left or down) A negative acceleration can mean –a decrease in velocity, or –an increase in velocity in the negative direction (left or down)

7. Turn to page 357 and calculate acceleration for each diagram