Free Fall Chapter 3

Free Fall In the absence of air resistance, all objects experience the same downward acceleration – whether they are moving UP or DOWN In other words, in a vacuum (where there is no air) all objects will fall at the same rate. Free fall acceleration on Earth (g) is -9.81m/s2 Heavier objects do not fall faster than lighter objects

Remember: up is (+) positive down is (-) negative Displacement can be positive or negative Velocity can be positive or negative Acceleration can be positive or negative However – acceleration due to gravity is always negative!

Picture this: A ball is thrown upward with initial velocity (+v) It has negative acceleration (-a) so the speed decreases The ball reaches maximum height and stops for an instant [v = 0m/s] BUT a = -9.81m/s2 still! If acceleration were to change to 0, then the ball would not move from its position. ‘g’ never stops acting on objects! The ball falls back toward the ground (-v). Since acceleration is in the same direction as velocity, the speed increases.

How fast: The velocity of an object in free fall changes by 9.81m/s each second. How far: The distance an object travels each second also changes because the speed is changing each second.

Equations: Use the same ones as before just remember that a= -9.81m/s2 whenever an object is moving vertically on Earth.

Displacement is negative because the object moved down 1. King Kong carries Fay Wray up the 321m tall Empire State Building. At the top, her shoe falls off. How fast will her shoe be falling just before it hits the ground? Displacement is negative because the object moved down d = -321m vi =0m/s a = -9.81m/s2 vf = ? When an object is dropped or falls, the initial velocity is zero

2. A baby blue jay sits in a tall tree waiting for its dinner 2. A baby blue jay sits in a tall tree waiting for its dinner. As the mother lands on the nest she tries to drop a worm into the chick’s mouth, but misses. The worm falls to the ground in 1.50s. How high up is the nest?

3. A flea falls off the top of a giraffe’s head which is 6m from the ground. How long does it take the flea to plummet to the ground?

4. In order to open a clam it catches, a seagull will drop the clam repeatedly onto a hard surface from high in the air until the shell cracks. If the seagull drops a clam from a height of 25.0m, how long will the clam take to fall to the rock below?

5. At Great Adventure a ride called “Free Fall” carries passengers up to a height of 33.5m and drops them to the ground. How fast are the passengers going just before they reach ground level?

6. A dog (accidently falls) from a bridge to pit of spikes 12.0m below. With what speed does the dog hit the spikes?