## Free Fall

AP Physics C Mrs. Coyle

### Free Fall

An object moving under the influence of gravity only. 

g

= -9.80 m/s 2 , downwards   No air resistance.

Free fall is uniform accelerated motion. (g is constant throughout the motion.) 

Galileo:

all objects fall with the same acceleration. He used his ball and channel experiment.

Remember? Galileo’s Ball and Channel Experiment

He raised the channel to a level that simulates gravity?

http://www.ifa.hawaii.edu/~barnes/ast110_06/rots/pftim19_01.png

Examples:  Dropped   Thrown downward Thrown upward

o

### = 0

Position (m) o Time (s) Parabola

o

### = 0

What is the velocity and acceleration at the top of the motion?

### Example 1

 A ball thrown vertically upward is caught by the thrower after 20.0 s. Find (a) the initial velocity of the ball and (b) the maximum height it reaches.

 Answer: a) 98.0 m/s, b) 490 m

Example 2  Another scheme to catch the roadrunner has failed. A safe falls from rest from the top of a 25.0m high cliff toward Coyote, who is standing at the base. Coyote first notices the safe after it has fallen 15.0 m. How long does he have to get out of the way?