Revision summary

Average speed

Total distance / total elapsed time. Include stops. Unit: m/s.

Acceleration

(v - u) / t. Constant throughout a uniform interval; otherwise an average. Unit: m/s².

Free fall near Earth

g is approximately 10 m/s² downwards. Air resistance is neglected.

Measure free-fall acceleration

Two light gates time the passage of the same short flag. Speed = flag length / blocked duration. For approximately uniform acceleration, assign each speed to the midpoint of its blocked interval, then use the time between those midpoints in a = (v - u) / t. The supplied speeds 1.00 and 2.00 m/s at 0.0100 and 0.1120 s give about 9.8 m/s² downwards. This is a free-fall determination only if other forces are negligible. Align the flag and gates, use a suitable timer and keep the attached body out of the beam; repeats do not fix a wrong flag length or time interval.

Check your answer

• Identify the axes and the time interval.
• Use changes on both axes for a gradient.
• Split graph areas into rectangles and triangles; triangle area = (1/2) x base x height.
• Give units, and direction when the quantity needs it.
• State assumptions such as uniform acceleration or negligible air resistance.
• Separate negative velocity, negative acceleration and slowing down. They do not mean the same thing.