Free Fall: Acceleration, Kinematics, and Measurement

All flashcards

What is free fall?

Free fall is motion in which gravity is the only significant force affecting an object; air resistance and friction are negligible.

What is the average value of $g$ near Earth's surface?

The average magnitude is $9.80\,\text{m/s}^2$, directed downward toward the center of Earth.

Why do objects of different masses have the same free-fall acceleration?

At a given location, gravitational acceleration is independent of an object's mass when air resistance and friction are negligible.

What does air resistance do?

Air resistance opposes an object's motion through air and can affect how quickly different objects fall.

How does the sign of gravitational acceleration depend on the coordinate system?

If upward is positive, acceleration is $-g$; if downward is positive, it is $+g$. Gravity physically points downward in both cases.

Quiz questions

1. At the highest point of an object’s vertical path, which statement is correct in an upward-positive coordinate system?Answer: Its vertical velocity is zero momentarily, and its acceleration is $-g$.
2. With upward positive, which equation gives vertical position after time $t$ for constant gravitational acceleration?Answer: $y=y_0+v_0t-\frac{1}{2}gt^2$
3. An object is moving downward after its speed is found by taking the square root of a squared-velocity equation. If upward is positive, which velocity sign should be used?Answer: The negative sign, because downward is negative.
4. An object dropped from rest falls a displacement $y-y_0$ in time $t$. With upward positive, which expression estimates its acceleration?Answer: $a=\frac{2(y-y_0)}{t^2}$
5. A ruler falls a distance $d$ from rest before being caught. Which expression estimates the reaction time, using gravitational acceleration magnitude $g$?Answer: $t=\sqrt{\frac{2d}{g}}$