Non-uniform motion
Cambridge A-Level Physics (9702) · Unit 3: Dynamics · 7 flashcards
Non-uniform motion is topic 3.2 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 3 — Dynamics , alongside Linear momentum and its conservation. In one line: Drag force is a resistive force that opposes the motion of an object through a fluid (liquid or gas). It increases with the object's speed and depends on factors like the object's shape and the fluid's viscosity. Air resistance is a type of drag force.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 1 definition and 6 key concepts — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Drag force
Drag force is a resistive force that opposes the motion of an object through a fluid (liquid or gas). It increases with the object's speed and depends on factors like the object's shape and the fluid's viscosity. Air resistance is a type of drag force.
What the Cambridge 9702 syllabus says
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- show a qualitative understanding of frictional forces and viscous/drag forces including air resistance (no treatment of the coefficients of friction and viscosity is required, and a simple model of drag force increasing as speed increases is sufficient)
- describe and explain qualitatively the motion of objects in a uniform gravitational field with air resistance
- understand that objects moving against a resistive force may reach a terminal (constant) velocity
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Non-uniform motion
- › Recall that at terminal velocity, speed is constant, and therefore the kinetic energy remains constant, resulting in a horizontal line on the graph.
- › Define force using the general term 'rate of change of momentum' to ensure your answer applies to systems with varying mass.
- › Distinguish momentum (mv) from force (the rate of change of momentum) in all written explanations.
- › In velocity-time or displacement-time graphs involving terminal velocity, the initial gradient at release must equal g if air resistance is initially zero.
- › State clearly that at terminal velocity, Weight = Upthrust + Viscous Force, then solve for the unknown value.
Describe the effect of air resistance on a falling object's acceleration.
Air resistance opposes the motion of the object, resulting in a net force that is less than the object's weight. This reduces the object's acceleration. As speed increases, air resistance increases, further reducing acceleration.
Explain how an object reaches terminal velocity when falling through air.
As an object falls, air resistance increases with speed. Eventually, the air resistance equals the object's weight. At this point, the net force is zero, and the object stops accelerating, reaching a constant terminal velocity.
What is a drag force?
Drag force is a resistive force that opposes the motion of an object through a fluid (liquid or gas). It increases with the object's speed and depends on factors like the object's shape and the fluid's viscosity. Air resistance is a type of drag force.
State the relationship between speed and drag force.
Drag force generally increases as speed increases. A simple model suggests drag force is proportional to the square of the speed (F ∝ v²).
Describe qualitatively how friction affects the motion of a sliding object.
Friction is a force that opposes motion between two surfaces in contact. It acts to slow down or prevent the sliding object from moving. The friction force converts kinetic energy into heat.
How does air resistance affect the range of a projectile?
Air resistance reduces the horizontal range of a projectile. It opposes the projectile's motion, decreasing its horizontal velocity and causing it to slow down, leading to a shorter distance traveled.
Explain why a heavier object may reach a higher terminal velocity compared to a lighter object of the same shape.
A heavier object experiences a greater gravitational force (weight). Therefore, a greater drag force is required to balance the weight and reach terminal velocity. Since drag force increases with speed, the heavier object needs to fall faster to achieve a larger drag force, resulting in a higher terminal velocity.
Review the material
Read full revision notes on Non-uniform motion — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 3 — Dynamics
Non-uniform motion sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Non-uniform motion deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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