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
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Show a qualitative understanding of friction and of viscous (drag) forces, air resistance among them. Coefficients of friction and viscosity are not needed; a simple model where drag grows as speed grows is enough.
- Describe and explain, qualitatively, how objects move in a uniform gravitational field when air resistance acts on them.
- Understand that an object moving against a resistive force can reach a constant velocity, called terminal 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.
- › On a velocity-time graph for a falling object reaching terminal velocity, the initial gradient at release equals g if air resistance is initially zero.
- › State clearly that at terminal velocity, Weight = Upthrust + Viscous Force, then solve for the unknown value.
- › Recognize that drag force depends on velocity and the properties of the fluid, not the hydrostatic pressure at depth.
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
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