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KS3 Combined Science

Forces and motion

52 questions5 subtopics
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What's covered

Forces12
Hooke's Law10
Newton's laws10
Pressure in fluids10
Speed, distance and time10

Key facts

1

Hooke's Law

The elastic limit is the point beyond which a spring is permanently deformed and will no longer return to its original length when the force is removed.

2

Newton's laws

From F = ma: acceleration = F ÷ m; the greater the force for a fixed mass, the greater the acceleration; the greater the mass for a fixed force, the smaller the acceleration.

3

Hooke's Law

The elastic potential energy stored in a stretched spring is E = ½ke² (half the spring constant times the extension squared).

4

Newton's laws

A falling object accelerates due to gravity (10 m/s²) until air resistance equals its weight; then it falls at constant terminal velocity with zero acceleration.

5

Hooke's Law

A stretched or compressed spring stores energy in its elastic potential store, which is released when the spring returns to its original shape.

6

Newton's laws

With no air resistance, all objects fall with the same acceleration (about 10 m/s² on Earth) whatever their mass, so a heavy and a light object dropped together hit the ground at the same time.

7

Hooke's Law

On a force-extension graph for a spring obeying Hooke's Law, the gradient of the straight-line portion represents the spring constant.

8

Newton's laws

Inertia is the tendency of an object to resist a change in its motion; more massive objects have greater inertia.

9

Hooke's Law

Hooke's Law equation: force = spring constant × extension (F = ke), where k is the spring constant and e is the extension.

10

Newton's laws

One newton (N) is the force required to give a mass of 1 kg an acceleration of 1 m/s² — directly from F = ma.

Sample questions

A taste of the 52 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.

1Forces

What is a force?

  • ✓A push or pull on an object
  • •A type of energy store
  • •Speed of an object
  • •The mass of an object
2Hooke's Law

What is the equation for Hooke's Law?

  • •F = k/e
  • ✓F = ke
  • •F = ke²
  • •F = ma
3Newton's laws

What does Newton's first law say about an object with no resultant force on it?

  • •It always slows down and eventually stops
  • •It changes direction but keeps the same speed
  • •It speeds up steadily in the direction it faces
  • ✓It stays still or keeps moving at constant velocity
4Pressure in fluids

What is the equation for pressure?

  • •P = A/F
  • •P = F × A
  • ✓P = F/A
  • •P = F/d
5Speed, distance and time

What is the equation for speed?

  • ✓speed = distance ÷ time
  • •speed = distance × time
  • •speed = force ÷ mass
  • •speed = time ÷ distance
6Forces

Which is a contact force?

  • •Electric force
  • ✓Friction force
  • •Gravity force
  • •Magnetic force

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