FREE FALL

Freely falling

If air resistance is disregarded, all objects dropped near the surfaceof a planet fall with the same constant acceleration. This accelerationis due to gravitational force, and the motion is referred to as free fall.

Freely falling

The acceleration due to gravity is denoted with the symbols ag (generally)or g (on Earth’s surface). The magnitude of g is about 9.81 m/s2.

Acceleration is constant during upward and downward motion

In the photograph on the left, the upward displacement of the ballbetween each successive image is smaller and smaller until the ball stops and finally begins to move with an increasing downward velocity, as shown on the right.

Formulas

A robot probe drops a camera off the rim of a 239 m high cliff on Mars, where the free-fall acceleration is −3.7 m/s2.a. Find the velocity with which the camera hits the ground.b. Find the time required for it to hit the ground.

A flowerpot falls from a windowsill 25.0 m above the sidewalk.

a. How fast is the flowerpot moving when it strikes the ground?b. How much time does a passerby on the sidewalk below have to move out of the way before the flowerpot hits the ground?

A tennis ball is thrown vertically upward with an initial velocity of +8.0 m/s.

a. What will the ball’s speed be when it returns to its starting point?b. How long will the ball take to reach its starting point?

Jason hits a volleyball so that it moves with an initial velocity of 6.0 m/s straight upward. If the volleyball starts from 2.0 m above the floor, how long will it be in the air before it strikes the floor?