Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall Newton’s first law and use it in the following situations: a where…
Full specification wording
Topic 2 – Motion and forces: 2.14 Recall Newton’s first law and use it in the following situations: a where the resultant force on a body is zero, i.e. the body is moving at a constant velocity or is at rest b where the resultant force is not zero, i.e. the speed and/or direction of the body change(s)
Newton's first law states that a body stays at rest, or keeps moving at constant velocity, unless a resultant force acts on it.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 14 of 32
Study notes
From the checked teaching notes for this specification point.
The idea
Newton's first law states that a body stays at rest, or keeps moving at constant velocity, unless a resultant force acts on it. Apply it in two situations. (a) When the resultant force is zero, the body is either at rest or moving at constant velocity: a car cruising at a steady 20 m/s on a straight road has balanced driving and resistive forces, so its velocity does not change. (b) When the resultant force is not zero, the speed and/or the direction of the body changes: an unbalanced force makes a moving object speed up, slow down or change direction, and makes a stationary object start to move. Constant velocity does not require a force to keep it going; it requires zero resultant force.
What earns the marks
- States Newton's first law: a body remains at rest or moves at constant velocity unless acted on by a resultant force.
- Explains that a zero resultant force means the body is at rest or moving at constant velocity.
- Explains that a non-zero resultant force changes the speed and/or the direction of the body.
- Applies the law to a named situation, identifying whether the resultant force is zero or not and the resulting motion.
Common mistakes and how to put them right
Claims a moving object needs a continuous forward force to keep moving at constant velocity.
Put it right: State that zero resultant force gives constant velocity.
Confuses balanced forces with no forces at all.
Put it right: Balanced forces give a zero resultant force, which is what matters.
Says an unbalanced force always changes only the speed.
Put it right: Recognise that it can change direction as well.
Assumes a body at rest must have no forces acting on it.
Put it right: A body at rest can have balanced forces giving zero resultant.
Exam tips
- Quote the law in full, including both 'at rest' and 'constant velocity'.
- For each situation, first decide whether the resultant force is zero, then state the effect on motion.
- Use the phrase 'resultant force' rather than 'force' to show you mean the net effect.
- Link direction changes to a non-zero resultant force, not only speed changes.
Try the lesson
The start of the Topic 2 – Motion and forces: 2.14 Recall Newton’s first law and use it in the following situations: a where the resultant force on a body is zero, i.e. the body is moving at a constant velocity or is at rest b where the resultant force is not zero, i.e. the speed and/or direction of the body change(s) lesson, made from checked teaching notes for this specification point.
Have a go first
A book is lying still on a table. According to Newton's first law, what can be said about the forces acting on it?
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Test your understanding of Topic 2 – Motion and forces: 2.14 Recall Newton’s first law and use it in the following situations: a where the resultant force on a body is zero, i.e. the body is moving at a constant velocity or is at rest b where the resultant force is not zero, i.e. the speed and/or direction of the body change(s)
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