Use of appropriate apparatus and techniques for measuring motion,…

The idea

This practical activity requires you to choose apparatus that suits the motion being studied and to use it so that speed and the rate of change of speed can be found. For steady motion over a measured distance, use a metre rule or tape to measure the distance and a stopwatch or light gates to measure the time; speed equals distance divided by time. For changing motion, light gates at two points give the speed at each point, and dividing the change in speed by the time between the gates gives acceleration or deceleration. A ticker-timer or a video with frame analysis can also record position at equal time intervals. Record repeat readings, keep units consistent and identify whether the value is speeding up or slowing down.

What earns the marks

• Selects apparatus suited to the motion, such as light gates for instantaneous speed or a stopwatch and tape for average speed over a measured distance.
• Measures the distance travelled with a metre rule or tape and the time with a stopwatch or data logger, then calculates speed as distance divided by time.
• Determines the rate of change of speed by dividing the change in speed between two points by the time taken between them.
• States whether the calculated rate of change represents acceleration or deceleration according to whether speed increases or decreases.
• Records repeat readings and uses consistent SI units such as metres and seconds when reporting speed in m/s and acceleration in m/s².

Common mistakes and how to put them right

• Confuses average speed over a whole journey with instantaneous speed at one point.

  Put it right: Use light gates or short intervals to obtain instantaneous speed.

• Divides distance by time to find acceleration.

  Put it right: Divide the change in speed by the time taken instead.

• Omits the direction of the change and so cannot say whether the motion is acceleration or deceleration.

  Put it right: Compare the two speeds to decide.

• Mixes units such as centimetres and seconds without converting.

  Put it right: Convert all lengths to metres before calculating.

Exam tips

• Read the question to see whether it asks for speed, acceleration or deceleration before choosing a formula.
• Show the measurements taken and the substitution into the equation so the method is visible.
• Check the sign or wording of the answer: a decreasing speed means deceleration, not negative acceleration described as speeding up.