# Newton's First Law

## Key Stage 4

### Meaning

Newton's First Law states that "An object in motion will tend to stay in motion in a straight line and an object at rest will tend to stay at rest unless an unbalanced force acts upon it."

Newton's First Law describes the fact that:
If the resultant force on an object is zero then it will continue to move at a constant velocity.
If the resultant force on an object is not zero then an object will accelerate (change speed or direction).
This means that if an object is observed changing speed or direction then there must be an unbalanced force acting on it.

### Examples

Stationary Object - The object remains at rest because the forces and balanced.

Uniform Velocity - The object remains at a constant speed and continues in a straight line because the forces acting on the object are balanced.

Uniform Speed but Changing Velocity - The object is changing direction because there are unbalanced forces acting on it.

Changing Speed - The object is changing speed because there are unbalanced forces acting on it.

### References

#### AQA

Newton’s First Law of motion, page 118, GCSE Physics; Third Edition, Oxford University Press, AQA
Newton’s First Law, page 212, GCSE Combined Science; The Revision Guide, CGP, AQA
Newton’s first law, page 64, GCSE Physics; The Revision Guide, CGP, AQA
Newton’s First Law, pages 162, 163, GCSE Combined Science Trilogy; Physics, CGP, AQA
Newton’s First Law, pages 194, 195, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA

#### Edexcel

Newton’s First Law, page 149, GCSE Combined Science; The Revision Guide, CGP, Edexcel
Newton’s First Law, pages 14-15, GCSE Physics, Pearson Edexcel
Newton’s First Law, pages 298-299, GCSE Combined Science, Pearson Edexcel
Newton’s First Law, pages 33, 34, GCSE Physics, CGP, Edexcel