大象传媒

Force and Newton's laws - CCEANewton鈥檚 First Law

In 1687, Isaac Newton created three laws of motion to describe the relationship between a body and the forces acting upon it, and how the body moves in response to those forces.

Part of Physics (Single Science)Force

Newton鈥檚 First Law

Balanced forces

This simply means that balanced forces, acting on the same object, will have no effect on the motion of an object.

In practice this means:

  • it could be , or;
  • it could be moving at constant speed in a straight line (constant velocity).

Example

The forces acting on this car are balanced.

A car with 2 forces acting either side of it. On the left is Drag, which measures 5,000 newtons. On the right is Thrust, which also measures 5,000 newtons.
Figure caption,
Car moving forward at 20 m/s

The thrust from the engine is equal and opposite to the drag caused by air resistance and between the road and car tyres.

There is no resultant (or net) force as the forces add up to zero.

The car will continue to travel forward with a speed of 20 m/s in a straight line.

Example

A car with 2 forces acting on it. The downward force is labelled 'Weight'. The upward force is labelled 'Normal reaction force of ground on car'.
Figure caption,
These forces balance. The car is still.

The upward force equals the downward force and they both act on the car.

The car remains at rest. It does not move upwards or downwards.

Balanced forces have no effect on an object.

If it is at rest, it remains at rest.

If it is moving at constant speed in a straight line, it continues to move at the same speed in the same straight line.