Lesson 2.3 Falling Objects Essential Question: How do you calculate the displacement, velocity and time of falling objects?

Think about a pen and piece of paper falling to the ground Think about a pen and piece of paper falling to the ground. Which will hit the ground first? What is the piece of paper is crumpled?

On August 2, 1971, a demonstration was conducted on the moon by astronaut David Scott. He simultaneously released a hammer and a feather from the same height above the moon’s surface. The hammer and feather both fell straight down and landed on the lunar surface at exactly the same moment. Although the hammer is more massive than the feather, both objects fell at the same rate.

A feather and an apple are released from rest in a vacuum chamber A feather and an apple are released from rest in a vacuum chamber. The two objects fell at exactly the same rate, as indicated by the horizontal alignment of the multiple images. The time intervals are equal but the displacements are not. As a result, the velocity isn’t constant so the two objects are accelerating.

If air resistance is disregarded, all objects dropped near the surface of a planet will fall with the same constant acceleration. The only thing affecting the falling object is gravity.

What is free fall? The motion of a body when only the force due to gravity is acting on the body Freely falling bodies undergo constant acceleration 𝑎 𝑔 or 𝑔 𝑔=−9.81 m s 2

What happens when you throw an object in the air? It will continue to move upward for some time, stop momentarily at the peak, and then change direction and begin to fall. Objects thrown in the air have a downward acceleration as soon as they are released.

This is a strobe photograph of a ball thrown up into the air with an initial velocity of +10.5 m/s.

The Ball’s Velocity v. Time On this velocity-time graph, the slope of the line, which is equal to the ball’s acceleration, is constant from the moment the ball is released and throughout its motion.

Is there always downward acceleration on freely falling objects? Yes! The downward acceleration is the same when an object is moving up, when it is at rest at the top of its path, and when it is moving down.

When an object is thrown up in the air, it has a positive velocity and a negative acceleration. At the top of its path, the object’s velocity has decreased until it is zero. When the object begins moving down, it has a negative velocity and its acceleration is still negative.

All objects that undergo free fall acceleration experience this same pattern. Objects that are falling toward Earth move faster and faster as they fall.

Jason hits a volleyball so that it moves with an initial velocity of 6 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?

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 s 2 . Find the velocity with which the camera hits the ground. Find the time required for it to hit the ground.

A flowerpot falls from a windowsill 25. 0 m above the sidewalk A flowerpot falls from a windowsill 25.0 m above the sidewalk. How fast is the flowerpot moving when it strikes the ground? 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. What will the ball’s speed be when it returns to its starting point? How long will the ball take to reach its starting point?

How do you calculate the displacement, velocity and time of falling objects?