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## AP®︎/College Physics 1

### Unit 1: Lesson 7

Objects in freefall

# Freefall review

Review the key concepts and skills for acceleration due to gravity, including analyzing motion of objects in freefall.

## Key terms

TermMeaning
Acceleration due to gravityIn the absence of air resistance, all objects fall with constant acceleration start text, g, end text toward the surface of the Earth. On the surface of Earth, defined as g, equals, 9, point, 8, start fraction, start text, m, end text, divided by, start text, s, end text, squared, end fraction.

## Analyzing motion for objects in freefall

Freefall is a special case of motion with constant acceleration, because acceleration due to gravity is always constant and downward. This is true even when an object is thrown upward or has zero velocity.
For example, when a ball is thrown up in the air, the ball's velocity is initially upward. Since gravity pulls the object toward the earth with a constant acceleration g, the magnitude of velocity decreases as the ball approaches maximum height.
Figure 1. Direction of velocity and acceleration for a ball thrown up in the air. Acceleration from gravity is always constant and downward, but the direction and magnitude of velocity change.
At the highest point in its trajectory, the ball has zero velocity, and the magnitude of velocity increases again as the ball falls back toward the earth (see figure 1).

## Common mistakes and misconceptions

People mistakenly think the final velocity for a falling object is zero because objects stop once they hit the ground. In physics problems, the final velocity is the speed just before touching the ground. Once it touches the ground, the object is no longer in freefall.