1.1.3Forces and Motion

Core Practical: Investigating Motion — Edexcel International GCSE Science Double Award 4SD0 - Physics Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 17

📚 Edexcel International GCSE Science Double Award 4SD0 - Physics Hub / Topical Revision

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Part 1 of 7The aim

This core practical investigates how objects move, using a trolley or a toy car on a ramp. You measure distance and time, calculate speed and, with more than one speed measurement, find the acceleration. You must be able to describe the method, identify the variables, process the results and evaluate the experiment.

A typical question: how does the speed (or acceleration) of a trolley depend on the angle of the ramp?

Part 2 of 7Apparatus and method

Typical apparatusa ramp or runway, a trolley, a metre rule, a stopwatch or light gates connected to a data logger, a card of known length attached to the trolley, and books or a stand to adjust the height.

Set the ramp at a chosen angle, with the lower end at a fixed position.

Mark the start line. Release the trolley from the same start line each time, without pushing.

With a stopwatch, measure the time for the trolley to travel a measured distance, such as 1.00 m. Calculate speed = distance ÷ time.

With light gates, a card of length L attached to the trolley breaks the beam for a time t, so the speed at the gate is L ÷ t.

Use two light gates (or one light gate that measures two intervals) to find the speed at two points and the time between them.

Change the independent variable (e.g. the height of the ramp), and repeat. Repeat each setting at least three times and calculate a mean.

The acceleration is found from a = (v − u) ÷ t, where u and v are the speeds at the two gates and t is the time between them (see 1.1.4).

Part 3 of 7Variables

Independent variable

Independent variable the one you change, such as the angle or height of the ramp.

Dependent variable

Dependent variable the one you measure, such as the speed at the bottom or the acceleration.

Control variables

Control variables things you keep the same, such as the mass of the trolley, the start position, the surface of the ramp, and the distance travelled.

For a fair test, only the independent variable should change. If the mass is also changed, you would not know which change caused the effect.

Part 4 of 7Errors and improvements

Human reaction time

(about 0.2 s) when using a stopwatch is a source of random error, which is large relative to short times. Using light gates removes this, and using a longer distance gives a longer time, and reduces the percentage error.

Starting the trolley with a slight push gives a systematic error. Release it from rest in the same way.

Friction and air resistance affect the motion; use the same surface and a smooth runway.

Parallax errors when reading the ruler; look straight at the scale.

Repeat readings and discard outliers; calculate a mean to reduce random error.

Plot a graph of the dependent variable against the independent variable. Draw a line of best fit, which passes through or close to most points, and use it to describe the relationship, for example that acceleration increases as the ramp gets steeper.

Part 5 of 7Safety

Place a block or a buffer at the end of the runway to stop the trolley hitting the floor or the experimenter's feet, and keep the area free of obstacles. Use a stand firmly clamped so the ramp cannot slip.

This practical uses ideas in 1.1.2 (speed), 1.1.4 (acceleration) and 1.1.5 (velocity-time graphs).

Part 6 of 7Presenting and analysing the data

Record your results in a table with headings that include units, such as 'Time / s'.

Presenting and analysing the data

Put the independent variable in the first column.

Give times to the same number of decimal places as the instrument allows (0.01 s for most stopwatches, though reaction time makes the real uncertainty about 0.2 s).

Calculate the mean time for each setting and then the speed, and plot the speed or acceleration on the vertical axis against the independent variable on the horizontal axis.

If the points lie close to a straight line through the origin, the quantities are directly proportional. A conclusion should refer to the data: for example, 'as the height of the ramp doubled, the acceleration also roughly doubled'. To evaluate, comment on how reliable the results were, which measurements were least accurate, and one change to improve the investigation.

Finally, state clearly the conclusion you can draw and the limits of the evidence: results from three repeats at five angles support a trend but do not prove an exact law.

Part 7 of 7Worked examples

A trolley travels 1.20 m down a ramp in times 1.52 s, 1.48 s and 1.50 s. Find the mean time and the average speed.
A card of length 0.050 m passes the first light gate in 0.025 s and the second in 0.010 s. The time between the gates is 0.40 s. Find the acceleration.
Why is it better to time 1.0 m than 0.1 m with a stopwatch?

Key terms

Term	Meaning
Independent variable	The variable you deliberately change.
Dependent variable	The variable you measure.
Control variable	A variable kept constant in order to make a fair test.
Light gate	A sensor that records the time for which a beam is broken.
Reaction time	Time delay between an event and a person's response, about 0.2 s.

Avoid these mistakes

Changing more than one variable at the same time, such as the angle and the mass.

Not releasing the trolley from rest at the same point each time.

Forgetting to repeat readings and take a mean.

Saying 'human error' without giving a specific cause, like reaction time.

Using the length of the card in cm in the equation with other values in m.

Last updated: 20 October 2026