AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
(HT only) The tendency of objects to continue in their state of rest or of…
Full specification wording
Newton's First Law: (HT only) The tendency of objects to continue in their state of rest or of uniform motion is called inertia.
Inertia is the tendency of an object to keep doing what it is already doing: staying at rest, or continuing to move with uniform velocity.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 8 of 8
Study notes
From the checked teaching notes for this specification point.
The idea
Inertia is the tendency of an object to keep doing what it is already doing: staying at rest, or continuing to move with uniform velocity. It is not a force and it does not cause motion; it explains why a resultant force is needed to change motion. A stationary book stays on a desk until a resultant force acts; a spacecraft coasting far from gravity continues at constant velocity because no resultant force acts. Inertia depends on mass: a larger mass has greater inertia, so a larger resultant force is needed to produce the same acceleration. This Higher Tier concept links directly to Newton’s First Law and prepares students for F = ma, where mass measures how strongly motion resists change.
What earns the marks
- Define inertia as the tendency to remain at rest or to continue moving with uniform velocity.
- State that inertia is not a force and does not itself change an object’s motion.
- Explain that a resultant force is required to overcome inertia and change speed or direction.
- Relate greater mass to greater inertia, so more force is needed for the same acceleration.
- Apply the idea to examples such as a passenger continuing forward when a bus brakes.
- Distinguish inertia from momentum and from the forces acting on an object.
Common mistakes and how to put them right
Calling inertia a force.
Put it right: Inertia is a property of matter, measured by mass, not a force.
Thinking heavy objects always fall faster because of inertia.
Put it right: In free fall without air resistance all masses accelerate equally.
Confusing inertia with momentum.
Put it right: Inertia depends on mass alone, while momentum depends on mass and velocity.
Exam tips
- Use the wording ‘tendency to continue in its state of rest or uniform motion’ when defining inertia.
- Link inertia to mass whenever a question asks why a heavier object is harder to accelerate or stop.
- Avoid saying inertia ‘pushes’ objects; describe the motion and the resultant force instead.
Try the lesson
The start of the Newton's First Law: (HT only) The tendency of objects to continue in their state of rest or of uniform motion is called inertia. lesson, made from checked teaching notes for this specification point.
Have a go first
What name is given to the tendency of an object to continue in its state of rest or of uniform motion?
Listen
Inertia is the tendency of an object to keep doing what it is already doing: staying at rest, or continuing to move with uniform velocity. It is not a force and it does not cause motion; it explains why a resultant force is needed to change motion. A stationary book stays on a desk until a resultant force acts; a spacecraft coasting far from gravity continues at constant velocity because no resultant force acts. Inertia depends on mass: a larger mass has greater inertia, so a larger resultant force is needed to produce the same acceleration. This Higher Tier concept links directly to Newton’s First Law and prepares students for F = ma, where mass measures how strongly motion resists change. A strong answer earns marks for these points. Define inertia as the tendency to remain at rest or to continue moving with uniform velocity. State that inertia is not a force and does not itself change an object’s motion. Explain that a resultant force is required to overcome inertia and change speed or direction. Relate greater mass to greater inertia, so more force is needed for the same acceleration. A common slip: Calling inertia a force. Instead, inertia is a property of matter, measured by mass, not a force. Exam tip: Use the wording ‘tendency to continue in its state of rest or uniform motion’ when defining inertia.
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