AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Newton's First Law: the object is stationary, the object remains stationary
Newton's First Law says that if the resultant force on an object is zero, its velocity does not change.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 3 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Newton's First Law says that if the resultant force on an object is zero, its velocity does not change. This statement covers the stationary case: an object already at rest stays at rest. 'Stationary' means its velocity is zero, so it is not moving and its direction is undefined. If all the forces on it balance, there is no resultant force to start it moving, so it remains stationary. For example, a book resting on a desk has weight acting downwards and a normal contact force acting upwards; these are equal and opposite, so the resultant force is zero and the book stays still. A student should identify the forces, show that they cancel, and conclude that the velocity stays at zero.
What earns the marks
- States that a stationary object has zero velocity and is not moving.
- Explains that when the resultant force is zero, there is no change in velocity.
- Applies the idea to a named example, such as a book on a desk or a parked car.
- Identifies the balanced forces acting on the object, for example weight and the normal contact force.
- Concludes that because the resultant force is zero, the object remains stationary.
Common mistakes and how to put them right
Saying that no forces act on a stationary object.
Put it right: Forces do act but they balance, giving a resultant force of zero.
Confusing 'stationary' with 'constant speed'.
Put it right: Stationary means velocity is zero, whereas constant speed can be non-zero.
Claiming that a resultant force is needed to keep an object still.
Put it right: A resultant force would change its velocity, so zero resultant force keeps it still.
Exam tips
- Start by stating the resultant force is zero before concluding the object stays still.
- Name the balanced forces in your example rather than saying 'forces cancel' without detail.
- Use the word 'velocity' as well as 'stationary' to show you understand that velocity is zero.
Try the lesson
The start of the Newton's First Law: the object is stationary, the object remains stationary lesson, made from checked teaching notes for this specification point.
Have a go first
A book is resting on a table and is not moving. No resultant force acts on the book. What happens to the book?
Listen
Newton's First Law says that if the resultant force on an object is zero, its velocity does not change. This statement covers the stationary case: an object already at rest stays at rest. Stationary' means its velocity is zero, so it is not moving and its direction is undefined. If all the forces on it balance, there is no resultant force to start it moving, so it remains stationary. For example, a book resting on a desk has weight acting downwards and a normal contact force acting upwards; these are equal and opposite, so the resultant force is zero and the book stays still. A student should identify the forces, show that they cancel, and conclude that the velocity stays at zero. A strong answer earns marks for these points. States that a stationary object has zero velocity and is not moving. Explains that when the resultant force is zero, there is no change in velocity. Applies the idea to a named example, such as a book on a desk or a parked car. Identifies the balanced forces acting on the object, for example weight and the normal contact force. A common slip: Saying that no forces act on a stationary object. Instead, forces do act but they balance, giving a resultant force of zero. Exam tip: Start by stating the resultant force is zero before concluding the object stays still.
Key words
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Resultant force
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Balanced forces
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Velocity
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Newton's First Law
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See every definition
- Resultant force
- When this is zero, there is no change in velocity, so a stationary object remains stationary.
- Balanced forces
- Forces that are equal and opposite, so they cancel and give a resultant force of zero.
- Velocity
- For a stationary object this is zero, so it is not moving and its direction is undefined.
- Newton's First Law
- If the resultant force on an object is zero, its velocity does not change.
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