What is a gravitational field in the context of Cambridge International A Levels Physics?

In Cambridge International A Levels Physics, a gravitational field is defined as a region of space surrounding a mass where another mass experiences a force of gravitational attraction. This field is represented by field lines that indicate the direction of the force, and its strength is measured in newtons per kilogram (N/kg).

How is the strength of a gravitational field calculated?

The strength of a gravitational field, also known as gravitational field intensity, is calculated using the formula g = F/m, where F is the gravitational force experienced by a mass m placed in the field. Alternatively, it can be calculated using g = GM/r², where G is the gravitational constant, M is the mass creating the field, and r is the distance from the center of the mass.

What is the significance of gravitational field lines in Physics?

Gravitational field lines are a visual representation used in Physics to illustrate the direction and strength of a gravitational field. The lines point towards the mass creating the field, indicating the direction of the gravitational force. The density of these lines represents the field's strength; closer lines indicate a stronger field.

How does the concept of gravitational fields apply to planetary motion?

Gravitational fields play a crucial role in planetary motion by providing the centripetal force necessary to keep planets in orbit around stars. According to Newton's law of universal gravitation, the gravitational attraction between a planet and a star creates a field that governs the planet's elliptical orbit, as described by Kepler's laws of planetary motion.

What is the difference between gravitational field strength and gravitational potential?

Gravitational field strength is a vector quantity that measures the force per unit mass experienced by an object in a gravitational field, expressed in N/kg. In contrast, gravitational potential is a scalar quantity that represents the work done per unit mass to move an object from infinity to a point in the field, measured in joules per kilogram (J/kg). While field strength indicates the force's direction and magnitude, potential indicates the energy associated with a position in the field.

Why is "Treating $g$ as only an acceleration" a common mistake in Gravitational field?

Why it happens: Familiarity with g = 9.81 m/s². How to avoid it: Equivalent units: N/kg and m/s². Both correct. Source: 9702 Examiner Reports 2022-2024

Gravitational FieldsCambridge International A Level Physics 9702

Gravitational field

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next.

PreviousNext

Learn this Topic

Start with the slides for the quick version, then go deeper with the full study notes.

Short Study Notes in the form of Slides

Read the notes first. If the method in a worked example clicks, you're ready for the questions.

Short Study Notes — Gravitational field

Start with these resources to cover the key concepts, then work through the practice questions.

Page 1 / 0

Detailed Notes

Full prose, callouts and a recap — built for A* mastery, not just a quick scan.

Take these study notes with you

Download a branded PDF — full prose, callouts, recap and memorise list for Gravitational field, ready to print or save offline.

Gravitational Field Study Notes — Cambridge International A Level Physics 9702 (2025-2027 syllabus)

Definition of gravitational field strength. Field lines.

What you’ll learn

Mapped to the Cambridge International A Level 9702 syllabus (2025-2027).

13.1.1 — Define gravitational field strength.
13.1.2 — Sketch field lines.

Field strength

Force per unit mass.

Gravitational field. Region where a mass experiences a force.

Field strength. $g = F/m$ . Force on unit test mass. Vector, points toward source mass.

Units. N/kg, or equivalently m/s² (since $F = ma$ ).

Near Earth surface. $g \approx 9.81$ N/kg.

Cambridge tip. Mark scheme rewards 'force per unit mass'.

Force per unit mass.
Vector toward source.
$g \approx 9.81$ on Earth.

See the full worked example for gravitational field →

Field lines

Visualisation.

Conventions.

Direction of lines = direction of force on positive test mass.
Density of lines = strength of field.

Point mass. Radial inward lines.

Near Earth surface. Parallel downward (uniform).

Cambridge tip. Mark scheme rewards proper arrows + uniform spacing for uniform field.

Gravitational field lines point toward a mass: radially inward for a point mass and parallel downward (uniform) near a planetary surface.

Direction shows force on test mass.
Density shows strength.
Point mass: radial.

See the full worked example for gravitational field →

How it’s examined

Gravitational field on every A2 paper. Most-tested: $g$ definition (4-5 marks).

Sources: Cambridge International A Level Physics 9702 syllabus (2025-2027); 9702 Examiner Reports 2022-2024; 9702/42 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-11.

Master this Topic

Worked examples, formulae, definitions and the mistakes examiners flag — everything you need to push from a pass to an A*.

Take this whole topic with you

Download a branded revision sheet — worked examples, formulae, definitions and common mistakes for Gravitational field, ready to print or save as PDF.

Step-by-step worked examples — Gravitational field

Step-by-step solutions to past-paper-style questions on gravitational field, written exactly the way a tutor would explain them at the board.

1 $g$ definition (4 marks)
Extended• Adapted from 9702/42 May/Jun 2024• g
Question
Find $g$ at a location where a 5.0 kg mass weighs 49.0 N. (4 marks)
Step-by-step solution
1. Step 1
  $g = F/m$ .
  $g = 49.0/5.0 = 9.80 \text{ N/kg}$
Answer
$g = 9.80$ N/kg.
2Field lines (5 marks)
Extended• field lines
Question
Sketch and describe gravitational field lines for (a) point mass, (b) uniform field near Earth. (5 marks)
Step-by-step solution
1. Step 1
  (a) Point mass. Radial inward lines (like spokes pointing toward mass).
2. Step 2
  (b) Near Earth surface. Parallel downward lines (uniform field).
3. Step 3
  Direction = force on test mass. Spacing = field strength.
Answer
(a) Radial inward. (b) Uniform downward parallel.

Key Formulae — Gravitational field

The formulae you need to memorise for gravitational field on the Cambridge International A Level 9702 paper, with every variable defined in plain English and a note on when to use it.

Gravitational field strength
$g = \dfrac{F}{m}$
$F$
gravitational force on test mass $m$
When to use
Force per unit mass. Units: N/kg = m/s².

Key Definitions and Keywords — Gravitational field

Definitions to memorise and the exact keywords mark schemes credit for gravitational field answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9702 sitting.

Gravitational field
Examiner keyword
Region in which a mass experiences a force.
Gravitational field strength $g$
Examiner keyword
Force per unit mass at a point. $g = F/m$ . Units: N/kg = m/s².

Common Mistakes and Misconceptions — Gravitational field

The traps other students keep falling into on gravitational field questions — taken from recent Cambridge International A Level 9702 examiner reports and mark schemes — and how to avoid them.

✕Treating $g$ as only an acceleration
9702 Examiner Reports 2022-2024
Why it happens
Familiarity with $g = 9.81$ m/s².
How to avoid it
Equivalent units: N/kg and m/s². Both correct.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Video lesson

Short walkthrough of the concepts students most often get stuck on.

Gravitational field — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Gravitational field

Short Study Notes in the form of Slides

Short Study Notes — Gravitational field

Detailed Notes

What you’ll learn

How it’s examined

1ggg definition (4 marks)

2Field lines (5 marks)

Gravitational field strength

Gravitational field

Gravitational field strength ggg

✕Treating ggg as only an acceleration

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Gravitational field — frequently asked questions

1 $g$ definition (4 marks)

Gravitational field strength $g$

✕Treating $g$ as only an acceleration