2.1.8—The acceleration of free fall using a falling object

Near Earth, a falling object has approximately constant downward acceleration g when air resistance is negligible. Measure distance and time, then use s=½gt² from rest or a suitable model.

Repeat timings, reduce reaction-time error, use a light gate or video where possible, and plot quantities that test the assumed relationship.

A plot of fall distance s against t² has gradient g/2, so g is twice the fitted gradient.

The measured value can differ from 9.81 because of timing, height, drag or calibration; that does not redefine g.