Required practical - Force, mass and acceleration Revision Notes for AQA GCSE Physics Combined Science

Required practical - Force, mass and acceleration

What is this practical about?

This experiment helps you understand Newton's second law. You'll investigate how changing the force on an object affects its acceleration. The key relationship you're testing is that acceleration increases when force increases (if mass stays the same).

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This practical is fundamental to understanding motion in physics. It demonstrates one of the most important relationships in mechanics - how forces cause objects to accelerate.

Aim of the experiment

To investigate how force affects the acceleration of a moving object (a glider on an air track).

Equipment you need

The following specialised equipment is required for accurate measurements:

Linear air track - a long, smooth track with air holes
Gliders - objects that float on the air track
Light gates - electronic sensors that detect when objects pass through
Bench pulley - changes the direction of the string
String and weights - to pull the glider
Weight stack - different masses to change the pulling force
Clamps and stands - to support the equipment
Vacuum cleaner or air blower - provides air for the track

infoNote

The air track system eliminates friction, making this experiment much more accurate than using trolleys on a bench. The gliders effectively "float" on a cushion of air.

Method

Step 1: Set up the apparatus

Place the linear air track on a bench
Connect the air supply so gliders float smoothly
Position two light gates a short distance apart on the track
Attach string to the glider, run it over the pulley, and hang weights from it

Step 2: Take measurements

Switch on the air supply to start the glider moving
The light gates will automatically record the time taken for the glider to pass between them
Record the velocity readings from both light gates
Note the total force (weight of the hanging masses)

Step 3: Repeat with different forces

Change the number of weights to vary the pulling force
Take at least 5 different force measurements
Record all your results in a data table

Step 4: Calculate acceleration

Work out the acceleration using the relationship between velocity change and time
Use the formula: $a = \frac{v_2 - v_1}{t}$

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Worked Example: Calculating Acceleration

If your first velocity reading is $v_1 = 0.2 \text{ m/s}$ and your second reading is $v_2 = 0.8 \text{ m/s}$ , with a time difference of $t = 0.3 \text{ s}$ :

$a = \frac{v_2 - v_1}{t} = \frac{0.8 - 0.2}{0.3} = \frac{0.6}{0.3} = 2.0 \text{ m/s}^2$

Recording your results

Create a table with columns for:

Force (in Newtons)
First velocity reading
Second velocity reading
Time between readings
Calculated acceleration

Plot a graph of acceleration against force - it should show a straight line through the origin.

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The straight line relationship confirms that acceleration is directly proportional to force, which is exactly what Newton's second law predicts.

Important safety points

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Safety is Critical in This Experiment

Be very careful - a moving mass can be dangerous if it hits someone
Make sure the track is properly supported and cannot tip over
Don't let heavy weights fall freely - control their descent
Keep fingers away from moving parts, especially the pulley system
Ensure the area below the hanging weights is clear of people and equipment

Key physics concepts

Understanding these fundamental concepts is essential for this practical:

Velocity is how fast something moves in a particular direction. It's measured using: $v = \frac{\text{distance}}{\text{time}}$

Acceleration is how quickly velocity changes. It's calculated using: $a = \frac{\text{change in velocity}}{\text{time taken}}$

You need two velocity measurements and the time difference between them to work out acceleration.

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Remember that acceleration is a vector quantity - it has both magnitude and direction. In this experiment, we're measuring the magnitude of acceleration along the track.

Why use light gates?

Light gates and electronic equipment give much more accurate results than using a ruler and stopwatch. Human reaction time makes manual timing unreliable for fast-moving objects.

The advantages of electronic timing include:

Eliminates human reaction time errors
Provides precise time measurements
Allows for rapid data collection
Reduces measurement uncertainty

Your conclusion

The experiment should demonstrate that acceleration is directly proportional to force. This means:

Double the force → double the acceleration
Triple the force → triple the acceleration

This relationship is Newton's second law: $F = ma$ (Force = mass × acceleration)

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Understanding the Proportional Relationship

If you apply a force of 2 N and get an acceleration of 1 m/s², then:

A force of 4 N should give 2 m/s²
A force of 6 N should give 3 m/s²

This demonstrates the direct proportionality: $F \propto a$

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Key Points to Remember:

Acceleration increases when force increases (if mass stays constant)
Light gates are more accurate than manual timing methods
You need at least two velocity readings to calculate acceleration
The graph of acceleration vs force should be a straight line through the origin
This practical proves Newton's second law: $F = ma$
Safety first - moving masses can be dangerous if they hit someone

Required practical - Force, mass and acceleration (AQA GCSE Physics Combined Science): Revision Notes