Make the forces visible
Scalars have magnitude only; vectors have magnitude and direction. A free-body diagram should show all relevant forces acting on one object, with arrows in the correct directions and labels that identify the interaction.
GCSE Physics resources
AQA GCSE Forces
Scalars, Vectors and Free-Body Diagrams
Scalars have magnitude only; vectors have magnitude and direction. A free-body diagram should show all relevant forces acting on one object, with arrows in the correct directions and labels that identify the interaction.
Start here
The quick revision snapshot
Scalars have magnitude only; vectors have magnitude and direction. A free-body diagram should show all relevant forces acting on one object, with arrows in the correct directions and labels that identify the interaction.
By the end, you should be able to…
- Explain make the forces visible using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for Scalars, Vectors and Free-Body Diagrams. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
A force diagram represents one object, not the whole situation. Each arrow must be an interaction force with a clear direction: for example weight, normal contact force, thrust or drag. Motion arrows and pairs of Newton-third-law forces do not belong on the same free-body diagram.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Weight: W = mg (N, kg, N/kg). Newton’s second law: F = ma (N, kg, m/s²). Momentum: p = mv (kg m/s). Keep the unit next to each value while you substitute.
What a strong answer does
Choose the object, draw one arrow per force and then compare opposite directions to find the resultant. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
Free-body diagram builder
How does showing every force make the resultant easier to find?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
Example 1 · Classify quantities
Classify mass, velocity, distance and force as scalar or vector.
- Look for direction as well as size.
- Mass and distance have magnitude only.
- Velocity and force need direction.
Show the answer
Mass and distance are scalars; velocity and force are vectors.
Example 2 · Free-body diagram
A book rests on a table. Describe its free-body diagram.
- Choose the book only.
- Add weight down.
- Add normal contact force up.
Show the answer
Draw equal arrows: weight downward and normal contact force upward. Do not draw forces acting on the table.
Example 3 · Resultant force
A 12 N force acts right and an 8 N force acts left. Find resultant.
- Choose a positive direction.
- Subtract opposing forces.
- State direction.
Show the answer
Resultant force = 4 N to the right.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Adding Newton-third-law pairs to one free-body diagram.
- Calling speed a vector.
- Leaving force arrows unlabelled.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. State one scalar quantity.
[1 mark]Show answer and marking guidance
For example, mass, distance, time or speed.
2. State one vector quantity.
[1 mark]Show answer and marking guidance
For example, force, velocity, displacement or acceleration.
3. Explain why a free-body diagram includes only one object.
[3 marks]Show answer and marking guidance
It shows the forces acting on that chosen object, avoiding action-reaction forces on other objects.
4. A car has 500 N thrust and 500 N resistive force. State the resultant.
[2 marks]Show answer and marking guidance
Zero newtons.
5. State the direction of weight near Earth’s surface.
[1 mark]Show answer and marking guidance
Vertically downward, towards the centre of Earth.
6. Explain what a zero resultant force means for a moving object.
[3 marks]Show answer and marking guidance
It continues at constant velocity in a straight line.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in Scalars, Vectors and Free-Body Diagrams?
Forces questions often hide a simple model inside a diagram. Draw the forces, find the resultant, then connect the resultant to the motion or deformation.
How should I practise Scalars, Vectors and Free-Body Diagrams?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.