2.5Chapter 2: Forces

Planning fair tests: streamlining — Alhussan Physics - Stage 7 Revision Notes & Topical Questions

5 min read 8 parts Lesson 5 of 7 1 quiz

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Lesson summary

2.5 Planning fair tests: streamlining — Alhussan International Academy — Physics (Stages 7–9) notes: Plan a fair test of how shape affects motion through a fluid, write a conclusion and evaluate the investigation.Streamlined shape = a smooth, narrow profile that lets air or water…

Large flat front
Wind tunnels
Investigation question
Hypothesis
Prediction
Independent variable

Part 1 of 6What streamlining means

Streamlined shape

Streamlined shape a smooth, narrow profile that lets air or water flow past it easily, reducing the drag force.

Examples

Examples fish, dolphins, birds, bullet trains, racing cars and aeroplanes are streamlined.
Penguins and sharks have rounded fronts and tapering tails.
Swimmers shave their bodies and wear smooth suits, and cyclists wear teardrop helmets.

Large flat front

Large flat front a shape such as an open parachute gives a lot of resistance.

Benefit

Benefit reducing drag lets a vehicle travel faster or use less fuel.

Wind tunnels

Wind tunnels smoke or streamers show how air flows around a car model.
In a streamlined car the airflow stays smooth along the body,
- whereas in a boxy shape it separates behind the vehicle and forms swirling eddies that increase drag.

Part 2 of 6Asking a question and making a hypothesis

Question

Kasini wondered what affects how fast things can move through water after watching dolphins swim fast to catch fish.

Investigation question

Investigation question how does the shape of an object affect the time it takes to fall through water?

Hypothesis

Hypothesis engineers design cars and aeroplanes to be as streamlined as possible to reduce drag, so streamlined shapes should fall faster.

Prediction

Prediction a prediction is based on the hypothesis, such as a pointed teardrop shape falls faster than a flat disc.

Part 3 of 6Variables

Independent variable

Independent variable the shape of the clay.

Dependent variable

Dependent variable the time to fall through the water.

Control variables

Control variables the mass of clay, the volume and temperature of the water, the starting height and the release method.

Variable	Type
Shape	Independent
Fall time	Dependent
Mass, water volume, temperature, distance	Control

Part 4 of 6Plan and equipment

Shapes

Shapes make different shapes from the same amount of clay, such as a cone, cube, sphere, cylinder and cuboid.

Equipment

Equipment a large measuring cylinder holds the water, modelling clay makes the shapes, a stopwatch times the fall, a balance weighs equal masses and a measuring jug measures the water.

Results table

Results table the independent variable goes in the left column and the table has units in the headings, with columns for each time, the mean and the speed.

Part 5 of 6Carrying out the test

Mark two lines on the cylinder, such as 10 cm below the surface and 10 cm above the bottom,

so the object is moving at steady speed when timing begins.

Release each shape gently at the surface, without pushing it.

Time the fall between the lines with a stopwatch.

Repeat three times for each shape and calculate a mean.

Calculate speed = distance ÷ time.

Interpreting

Interpreting a smaller time or a higher speed shows lower drag.

Safety

Safety clean up spilled water to avoid slips and keep electrical equipment away.

Part 6 of 6Conclusion and evaluation

Presenting

Presenting plot a bar chart of the means because the data are categoric.
- (shape is described by words)

Conclusion

Conclusion state which shape was fastest, quote the speeds and say whether the prediction and hypothesis are supported.
Explain using dragthe object with the smallest front area and smoothest profile has the least drag and travels fastest.

Data quality

Data quality it was hard to see when to start and stop the stopwatch, and not enough measurements were taken to be sure they were correct.
A measurement for one shape could be an anomalous result because of a mistake.

Improvements

Improvements find a better method of timing such as a video camera, repeat the experiment several times for each shape, look for anomalous results and repeat them,
- and find the mean to make data more accurate.

Purpose of an evaluation

Purpose of an evaluation it should show how to collect better data, not make the experiment quicker or easier.
Repeating measurements enables you to identify anomalous results.

Key terms

Term	Meaning
Streamlined	shaped to reduce drag.
Drag	a resistive force from a fluid.
Fair test	a test where only one variable is changed.
Control variable	a variable kept constant.
Anomalous result	a result that does not fit the pattern.
Evaluation	a judgement of how good the method and data were.

Avoid these mistakes

Using different masses of clay — the mass must be a control variable.

Dropping from different heights — the starting height must be the same.

Pushing objects into the water — release them gently.

Timing only once — repeat and find a mean.

Last updated: 14 October 2026