Unit 7 · Circular Motion, Gravitational Fields and Oscillations
The Complete Cambridge International AS & A Level Physics (9702) Guide · Cambridge International AS & A Level Physics (9702)Unit 7 · Circular Motion, Gravitational Fields and Oscillations
- The Complete Cambridge International AS & A Level Physics (9702) Guide
- Cambridge International AS & A Level Physics (9702)
- 12 sections
Cambridge International does not publish a per-unit weighting for this exam. Exam structure (official): AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 2 questions, 23%); A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 2 questions, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 2 questions, 11.5%). Be ready to carry the same unit skills and representations into a complete answer on every paper. The 3.60 m/s velocity is tangential, but v²/r gives a 16.2 m/s² acceleration toward the center of the 0.800 m circle. Direction is part of the acceleration result.
- How Cambridge International AS & A Level Physics (9702) assesses this Cambridge International publishes no per-unit percentage for Cambridge International A Level Physics; Paper 1 accounts for 31% of the AS Level total and 15.5% of the A Level total. · AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 2 questions, 23%) | A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 2 questions, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 2 questions, 11.5%) · show the model with A graph of radial acceleration (m/s²) against speed (m/s)., A formula card that explains both radial acceleration and force contain the squared speed divided by radius., A table linking key concept, why it matters, visible method.
- Key skills Uniform Circular Motion: Angular Speed and Centripetal Acceleration (A Level), Gravitational Fields, Newton's Law of Gravitation and Circular Orbits (A Level), Gravitational Field of a Point Mass, Gravitational Potential and Potential Energy (A Level), Simple Harmonic Oscillations (A Level), Energy in Simple Harmonic Motion, Damping, Forced Oscillations and Resonance (A Level)
- How to study for Unit 7 This page turns A graph of radial acceleration (m/s²) against speed (m/s)., A formula card that explains both radial acceleration and force contain the squared speed divided by radius., A table linking key concept, why it matters, visible method. into one route: Use a = v²/r.
- The organizing decision At the marked instant, draw velocity tangent to the path and acceleration toward the center before evaluating either magnitude.
What Cambridge International AS & A Level Physics (9702) Unit 7 covers
Use this map to connect each assessed skill to the relationship or representation that makes it visible.
Uniform Circular Motion: Angular Speed and Centripetal Acceleration (A Level)
centripetal acceleration; gravitational potential; simple harmonic motion02Gravitational Fields, Newton's Law of Gravitation and Circular Orbits (A Level)
centripetal acceleration; gravitational potential; simple harmonic motion03Gravitational Field of a Point Mass, Gravitational Potential and Potential Energy (A Level)
centripetal acceleration; gravitational potential; simple harmonic motion04Simple Harmonic Oscillations (A Level)
centripetal acceleration; gravitational potential; simple harmonic motion05Energy in Simple Harmonic Motion, Damping, Forced Oscillations and Resonance (A Level)
centripetal acceleration; gravitational potential; simple harmonic motionCambridge International does not publish a per-unit weighting for this exam.
Official unit name and weighting: Cambridge International syllabus.
Circular Motion, Gravitational Fields and Oscillations
Connect the published share to the unit model
The 3.60 m/s velocity is tangential, but v²/r gives a 16.2 m/s² acceleration toward the center of the 0.800 m circle. Direction is part of the acceleration result.
Multiplying by 0.250 kg produces a 4.05 N inward resultant force. A negative scalar potential in a different context should not be confused with this radial vector direction.
The squared speed means a modest speed change can produce a larger force change. The graph makes that curvature visible while radius remains fixed.
Choose the inward radial direction or the oscillation equilibrium direction before writing equations. Relate the kinematics to force, field, potential or the simple-harmonic form, preserving the negative sign of scalar gravitational potential and the direction of vector acceleration. The final line should state the associated orbital, phase or energy implication, not only a magnitude.
The decision that organizes this unit
Define the system and choose the route before calculating
At the marked instant, draw velocity tangent to the path and acceleration toward the center before evaluating either magnitude.
Use a = v²/r
Mechanism route and repair branches
Relationships to preserve
- Radial acceleration: Speed is squared and radius is 0.800 m.
- Resultant force: The moving mass is 0.250 kg.
- Direction: Velocity is tangent to the circle.
Representations to read
- A graph of radial acceleration (m/s²) against speed (m/s).
- A formula card that explains both radial acceleration and force contain the squared speed divided by radius.
- A table linking key concept, why it matters, visible method.
Branches to reject
- Using v/r and losing one power of speed
- Treating acceleration as the force
- Giving magnitudes without their radial direction
| Key concept | Why it matters | Visible method |
|---|---|---|
| Radial acceleration | Speed is squared and radius is 0.800 m | Use a = v²/r |
| Resultant force | The moving mass is 0.250 kg | Multiply 16.2 m/s² by mass |
| Direction | Velocity is tangent to the circle | State acceleration and force as inward |
| Radial direction | Circular acceleration is a vector directed inward. | State the direction as well as the magnitude. |
| Signed potential | Gravitational potential is scalar but can be negative. | Preserve its sign separately from vector acceleration. |
How Cambridge International AS & A Level Physics (9702) assesses Circular Motion, Gravitational Fields and Oscillations
What a complete response must make visible
Match the task to evidence that a reader can audit, then check the most likely reasoning failure before finalizing the response.
| Task | Evidence to show | Hurdle |
|---|---|---|
| Uniform Circular Motion: Angular Speed and Centripetal Acceleration (A Level) | centripetal acceleration; gravitational potential; simple harmonic motion | Using v/r and losing one power of speed |
| Gravitational Fields, Newton's Law of Gravitation and Circular Orbits (A Level) | centripetal acceleration; gravitational potential; simple harmonic motion | Treating acceleration as the force |
| Gravitational Field of a Point Mass, Gravitational Potential and Potential Energy (A Level) | centripetal acceleration; gravitational potential; simple harmonic motion | Giving magnitudes without their radial direction |
| Simple Harmonic Oscillations (A Level) | centripetal acceleration; gravitational potential; simple harmonic motion | Using v/r and losing one power of speed |
| Energy in Simple Harmonic Motion, Damping, Forced Oscillations and Resonance (A Level) | centripetal acceleration; gravitational potential; simple harmonic motion | Treating acceleration as the force |
Worked example: radial force, fields, potential and SHM
Read each question as it appears on the exam paper, choose your answer, then tap it to see the feedback.
Practice 1: Radial acceleration and force
A mass moves at constant speed in a horizontal circle.
A mass of 0.250 kg moves in a horizontal circle of radius 0.800 m at 3.60 m/s. Calculate (a) its centripetal acceleration and (b) the resultant force, stating both directions.
[4]Show all necessary working.
A. a = 16.2 m/s² inward; F = 4.05 N inward.
✅ Correct! 😊 Correct. The acceleration v²/r and the resultant force ma both point toward the center.
B. a = 16.2 m/s² tangential; F = 4.05 N inward.
❌ Not quite 😭 The magnitude is right, but centripetal acceleration is radial, not tangential. The tangential direction belongs to the instantaneous velocity.
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C. a = 4.50 m/s² inward; F = 1.13 N inward.
❌ Not quite 😭 This effectively uses v/r and omits the squared speed. Both calculated magnitudes are consequently too small.
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D. a = 16.2 m/s² outward; F = 4.05 N outward.
❌ Not quite 😭 These magnitudes are correct but both directions are reversed. The resultant force that maintains circular motion is toward the center.
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Full explanation
- Step 1Use centripetal acceleration a = v²/r because the speed and radius are given.
- Step 2Calculate a = (3.60 m/s)²/0.800 m = 16.2 m/s².
- Step 3Use F = ma = (0.250 kg)(16.2 m/s²) = 4.05 N.
- Step 4State that velocity is tangential while acceleration and resultant force are radially inward.
Practice 2: Acceleration in simple harmonic motion
An oscillator performs simple harmonic motion.
At one instant its displacement from equilibrium is +0.030 m and its angular frequency is 4.0 rad/s. Determine its acceleration and explain the sign.
[3]Show all necessary working.
A. a = ω²x, so the acceleration is positive and away from equilibrium.
❌ Not quite 😭 This drops the restoring minus sign. Simple harmonic acceleration is opposite to displacement, not away from equilibrium.
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B. a = −ω²x, so the acceleration is −0.48 m/s² and directed toward equilibrium.
✅ Correct! 😊 Correct. Substitution gives −(4.0)²(0.030) = −0.48 m/s², opposite to the positive displacement.
C. a = −ωx², so the acceleration is −0.0036 m/s².
❌ Not quite 😭 This squares the wrong quantity and is dimensionally inconsistent. Angular frequency, not displacement, must be squared.
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D. a = ωx, so the acceleration is 0.12 m/s² in the direction of motion.
❌ Not quite 😭 This has the dimensions of velocity and ignores the restoring direction. Acceleration is not generally in the direction of motion.
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Full explanation
- Step 1For simple harmonic motion, acceleration obeys a = −ω²x.
- Step 2Insert ω = 4.0 rad/s and x = +0.030 m.
- Step 3Calculate a = −(4.0)²(0.030) = −0.48 m/s².
- Step 4The negative sign shows that acceleration is toward equilibrium, opposite to the displacement.
Key terms for Unit 7: Circular Motion, Gravitational Fields and Oscillations
Models, uses, and boundaries
- Circular Motion, Gravitational Fields and Oscillations
- Both radial acceleration and force contain the squared speed divided by radius. Use this relationship when both radial acceleration and force contain the squared speed divided by radius..
- Worked example: radial force, fields, potential and SHM
- Using 3.60 m/s and 0.800 m yields 16.2 m/s² before the mass is introduced. Use this relationship when using 3.60 m/s and 0.800 m yields 16.2 m/s² before the mass is introduced..
- Circular Motion, Gravitational Fields and Oscillations: change one condition
- The graph compares acceleration values at different speeds while the orbit radius stays unchanged. Use this relationship when the graph compares acceleration values at different speeds while the orbit radius stays unchanged..
- Circular Motion, Gravitational Fields and Oscillations: test proposed results
- Any magnitude option remains incomplete unless its acceleration or force direction is inward. Use this relationship when any magnitude option remains incomplete unless its acceleration or force direction is inward..
Cambridge International AS & A Level Physics (9702) Unit 7 FAQ
How much of Cambridge International AS & A Level Physics (9702) does Unit 7 carry?
Cambridge International does not publish a per-unit weighting for this exam.
What is the first move on a Circular Motion, Gravitational Fields and Oscillations problem?
Use a = v²/r
Which relationships should I preserve?
Radial acceleration: Speed is squared and radius is 0.800 m. Resultant force: The moving mass is 0.250 kg. Direction: Velocity is tangent to the circle.
Which representations should I practice?
Practice moving among A graph of radial acceleration (m/s²) against speed (m/s)., A formula card that explains both radial acceleration and force contain the squared speed divided by radius., A table linking key concept, why it matters, visible method..
What error should I check before submitting an answer?
Check for Using v/r and losing one power of speed; Treating acceleration as the force; Giving magnitudes without their radial direction.
Evidence workshop
Continue from the free model into complete practice
The full unit guide continues with the chapter’s worked examples, figures, scoring tables, and answer checks.
- Worked example: radial force, fields, potential and SHM
- Circular Motion, Gravitational Fields and Oscillations: change one condition
- Circular Motion, Gravitational Fields and Oscillations: test proposed results
- Check the worked-example evidence for Circular Motion, Gravitational Fields and Oscillations
Full unit practice. Open the complete guide for the full evidence workshop and synthesis.
Related Cambridge International AS & A Level Physics (9702) unit guides
Cambridge International AS & A Level Physics (9702) Exam Guide & Review
The whole exam and its official unit sequence.01Physical Quantities and Units
Cambridge International does not publish a per-unit weighting for this exam.02Kinematics and Dynamics
Cambridge International does not publish a per-unit weighting for this exam.03Forces, Energy and Deformation of Solids
Cambridge International does not publish a per-unit weighting for this exam.04Waves and Superposition
Cambridge International does not publish a per-unit weighting for this exam.05Electricity and D.C. Circuits
Cambridge International does not publish a per-unit weighting for this exam.06Particle Physics
Cambridge International does not publish a per-unit weighting for this exam.08Thermal Physics
Cambridge International does not publish a per-unit weighting for this exam.09Electric Fields and Capacitance
Cambridge International does not publish a per-unit weighting for this exam.10Magnetic Fields and Alternating Currents
Cambridge International does not publish a per-unit weighting for this exam.11Quantum and Nuclear Physics
Cambridge International does not publish a per-unit weighting for this exam.12Medical Physics, Astronomy and Cosmology
Cambridge International does not publish a per-unit weighting for this exam.How to study Cambridge International AS & A Level Physics (9702) Unit 7
Start with the organizing decision
Before solving, restate the decision in operational terms: At the marked instant, draw velocity tangent to the path and acceleration toward the center before evaluating either magnitude.. Your first written move should be to Use a = v²/r.
Practice the same idea in several representations
Rotate through A graph of radial acceleration (m/s²) against speed (m/s)., A formula card that explains both radial acceleration and force contain the squared speed divided by radius., A table linking key concept, why it matters, visible method.. Use each representation to practice Uniform Circular Motion: Angular Speed and Centripetal Acceleration (A Level), Gravitational Fields, Newton's Law of Gravitation and Circular Orbits (A Level), Gravitational Field of a Point Mass, Gravitational Potential and Potential Energy (A Level), Simple Harmonic Oscillations (A Level), Energy in Simple Harmonic Motion, Damping, Forced Oscillations and Resonance (A Level), and explain what stays invariant when the surface form changes.
Turn each error into a repair check
After every attempt, audit the response for Using v/r and losing one power of speed; Treating acceleration as the force; Giving magnitudes without their radial direction. Then redo only the first step that made the reasoning diverge, keeping units, direction, and model conditions visible.
Confirm current course details in the official Cambridge International syllabus for the 2025-2027 administration.
Where to go next
Return to the Cambridge International AS & A Level Physics (9702) to see every unit and plan your revision.