Free Fall: Gravitational Acceleration, Kinematics, and Trajectories

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What is free fall?

Motion in which gravity is the only force acting, with air resistance and other frictional forces neglected.

Can an object be in free fall while moving upward?

Yes. After release, it is in free fall if gravity alone acts, whether it is rising or descending.

What does $g$ represent near Earth's surface?

The magnitude of gravitational acceleration, approximately $9.8\ \text{m/s}^2$ near Earth's surface.

Why do objects at the same location have equal gravitational acceleration in ideal free fall?

When air resistance is negligible, gravitational acceleration is independent of an object's mass.

What happens to acceleration at the highest point of an upward trajectory?

Velocity is momentarily zero, but acceleration remains downward with magnitude approximately $g$.

Quiz questions

1. With upward defined as positive, which equation gives vertical velocity after elapsed time $t$ in free fall?Answer: $v=v_0-gt$
2. Which constant-acceleration equation relates velocity to displacement without using elapsed time, with upward positive?Answer: $v^2=v_0^2-2g(y-y_0)$
3. At the highest point of an object’s upward free-fall trajectory, what are its velocity and acceleration?Answer: Velocity is zero; acceleration is still downward, $-g$ when upward is positive.
4. An object in free fall passes the same height once while rising and once while falling. What distinguishes its velocities at those passages?Answer: The velocity signs are opposite because the directions of travel differ.
5. Under what conditions can the constant-acceleration free-fall equations be used for vertical motion?Answer: Gravity is the only force and its acceleration is treated as constant.