Free Fall

1. Free Fall http://www.youtube.com/watch?feature=player_embedded&v=9YUtFpLpGfk

2. What is Freefall? A free falling object is an object that is falling under the sole influence of gravity. Any object that is being acted upon only by the force of gravity is said to be in a state of free fall.

3. Free Fall • There are two important motion characteristics that are true of free-falling objects: • Free-falling objects do not encounter air resistance. • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s/s

4. Value for Gravity • For the purposes of this class, we will assign an upward velocity as positive, and a downward velocity as negative. • Because gravity causes objects to move downward to the Earth, we will also assign a negative value to gravity (-9.8 m/s2)

5. Velocity • What does this mean for a ball dropped downward? • It gains velocity as it moves toward the ground • It’s final velocity will be negative

6. Example 1 • The time the Demon Drop at Cedar Point, OH is freely falling is 1.5 s. What is the velocity at the end of this time? How far does it fall? • We know: vf=? t= 1.5s vi= 0 m/s a= -9.8 m/s2

7. How far does it fall?

8. Velocity What does a negative acceleration mean for an object traveling away from the earth? • It loses velocity as it moves upward • It’s final velocity will reach zero • It will return to earth (assuming no other forces act on the object)

9. Example 2 A tennis ball is thrown straight up with an initial velocity of 22.5 m/s. It is caught at the same distance from the ground from which it was thrown. How high does the ball rise? How long does the ball remain in the air?

10. We know: d=25.8m

11. How long does the ball remain in the air? t= 2.3s, total time = 4.6 s

12. http://www.youtube.com/watch?v=Qw8OJJQ_hgk&feature=player_embeddedhttp://www.youtube.com/watch?v=Qw8OJJQ_hgk&feature=player_embedded