State Newton's law of universal gravitation.

Every point mass attracts every other point mass with a force proportional to the product of their masses and inversely proportional to the square of the separation of their centres.

Why is the minus sign sometimes written in front of the gravitational force equation?

It records that the force is attractive, acting in the opposite direction to the outward radial direction in which r is measured.

What is meant by an inverse square law?

A law in which the quantity falls in proportion to one divided by the square of the distance, so trebling the distance divides it by nine.

The separation of two masses is doubled. What happens to the gravitational force between them?

It falls to a quarter of its original value.

CCEA A-Level Physics 1210

Physical Quantities, Scalars and Vectors

Topic overview Physical quantities and SI base units Prefixes and standard form Scalars and vectors Resolving vectors and finding resultants Coplanar forces in equilibrium

Moments and Equilibrium

Topic overview Moment of a force Centre of gravity The principle of moments Determining unknown masses using moments

Linear Motion and Dynamics

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Newton's Laws of Motion

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Linear Momentum and Impulse

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Resistance and Resistivity

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Internal Resistance and Potential Dividers

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Waves

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Refraction

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Quantum Physics

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Wave-Particle Duality

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Astronomy

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Practical Skills and Data Analysis

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Deformation of Solids

Topic overview Hooke's law and the spring constant Elastic and plastic deformation and the elastic limit Stress, strain and the Young modulus Measuring the Young modulus of a wire Strain energy and force–extension graphs Choosing materials: strength, stiffness and cost

Thermal Physics

Topic overview Boyle's law, Charles's law and the pressure law The ideal gas equation pV = nRT The Avogadro constant, the mole and pV = NkT Internal energy and the distribution of molecular energy The kinetic theory equation pV = ⅓Nm⟨c²⟩Average molecular kinetic energy and temperature Absolute zero and the kelvin scale Specific heat capacity and the electrical method

Uniform Circular Motion

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Simple Harmonic Motion

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The Nucleus and Radioactive Decay

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Nuclear Energy, Fission and Fusion

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Gravitational Fields

Topic overview Fields of force and field lines Gravitational field strength Newton's law of universal gravitation The field strength of a point mass Circular motion of planets and satellites Kepler's third law Geostationary satellites

Electric Fields

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Capacitors

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Magnetic Fields

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Charged Particles and Accelerators

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Fundamental Particles

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Gravitational Fields

Newton's law of universal gravitation

3 things to know
Unit A2 2

Overview

Newton's law of universal gravitation and inverse square law.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Give the equation for the gravitational force between two point masses and define each symbol.

Key term

Give the value and unit of the gravitational constant G.

Key term

Under what condition may a large spherical body be treated as a point mass?

Questions from this subtopic

Each one with the model answer underneath.

1
State Newton's law of universal gravitation.
Model answer
Every point mass attracts every other point mass with a force proportional to the product of their masses and inversely proportional to the square of the separation of their centres.
2
Give the equation for the gravitational force between two point masses and define each symbol.
Model answer
F = GMm/r², where F is the force in newtons, G the gravitational constant, M and m the two masses in kilograms and r the separation of their centres in metres.
3
Give the value and unit of the gravitational constant G.
Model answer
G is 6.67 × 10⁻¹¹ N m² kg⁻².
4
Why is the minus sign sometimes written in front of the gravitational force equation?
Model answer
It records that the force is attractive, acting in the opposite direction to the outward radial direction in which r is measured.
5
What is meant by an inverse square law?
Model answer
A law in which the quantity falls in proportion to one divided by the square of the distance, so trebling the distance divides it by nine.
6
The separation of two masses is doubled. What happens to the gravitational force between them?
Model answer
It falls to a quarter of its original value.

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