AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Newton's First Law: Newton’s First Law:
Newton’s First Law describes what happens to an object’s motion when the forces on it balance.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Newton’s First Law describes what happens to an object’s motion when the forces on it balance. If the resultant force is zero, the object keeps doing what it was already doing: a stationary object stays at rest, and a moving object continues at the same speed in a straight line. This is why a puck sliding on frictionless ice keeps moving, and why a book resting on a table does not start moving on its own. The law is not about “no forces” — balanced forces can still act — but about the resultant being zero. It explains why seat belts are needed: a passenger keeps moving forward when a car stops suddenly because no resultant force acts on them during the brief interval.
What earns the marks
- State that Newton’s First Law applies when the resultant force on an object is zero.
- Explain that a stationary object remains stationary when the resultant force is zero.
- Explain that a moving object continues at constant speed in a straight line when the resultant force is zero.
- Distinguish between balanced forces and zero forces, noting that balanced forces give a zero resultant.
- Apply the law to a real context, such as a passenger continuing forward when a vehicle brakes sharply.
- Use the term resultant force correctly, meaning the single force that has the same effect as all the forces combined.
Common mistakes and how to put them right
Saying “no forces act” when the resultant is zero.
Put it right by stating that forces may be balanced, giving a zero resultant.
Claiming a moving object must have a forward force to keep moving.
Put it right by explaining that constant velocity needs zero resultant force, not a driving force.
Confusing constant speed with constant velocity.
Put it right by noting that a change of direction is a change of velocity and needs a resultant force.
Exam tips
- Always link your answer to the resultant force being zero, not just to “balanced forces”.
- When describing motion, state both the speed and the direction to show velocity is constant.
- Use a short everyday example, such as a ice skater or a car at steady speed, to make the application clear.
Try the lesson
The start of the Newton's First Law: Newton’s First Law: lesson, made from checked teaching notes for this specification point.
Have a go first
A book is resting on a table and does not move. What is the resultant force acting on the book?
Listen
Newton’s First Law describes what happens to an object’s motion when the forces on it balance. If the resultant force is zero, the object keeps doing what it was already doing: a stationary object stays at rest, and a moving object continues at the same speed in a straight line. This is why a puck sliding on frictionless ice keeps moving, and why a book resting on a table does not start moving on its own. The law is not about “no forces” — balanced forces can still act — but about the resultant being zero. It explains why seat belts are needed: a passenger keeps moving forward when a car stops suddenly because no resultant force acts on them during the brief interval. A strong answer earns marks for these points. State that Newton’s First Law applies when the resultant force on an object is zero. Explain that a stationary object remains stationary when the resultant force is zero. Explain that a moving object continues at constant speed in a straight line when the resultant force is zero. Distinguish between balanced forces and zero forces, noting that balanced forces give a zero resultant. A common slip: Saying “no forces act” when the resultant is zero. Instead, stating that forces may be balanced, giving a zero resultant. Exam tip: Always link your answer to the resultant force being zero, not just to “balanced forces”.
Key words
Say what each word means before you turn the card.
Resultant force
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Balanced forces
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Constant velocity
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See every definition
- Resultant force
- The single force that has the same effect as all the forces combined.
- Balanced forces
- Forces that may still act on an object but give a zero resultant.
- Constant velocity
- Motion at the same speed in a straight line, which needs zero resultant force.
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