# Newton's first law

According to Newton's first law of motion, an object remains in the same state of motion unless a acts on it. If the resultant force on an object is zero, this means:

• a stationary object stays stationary
• a moving object continues to move at the same

## Resultant forces

Two forces can be added together to find a resultant force. The resultant force is a single force that has the same effect as two or more forces acting together.

### Two forces in the same direction

The resultant force of two forces that act in the same direction can easily be calculated - to do this, just add the of the two forces together.

### Example

Two forces, 3 newtons (N) and 2 newtons (N), act to the right. Calculate the resultant force.

3 N + 2 N = 5 N to the right

### Two forces in opposite directions

Two forces that act in opposite directions produce a resultant force that is smaller than either individual force. It is often easiest to subtract the magnitude of the smaller force from the magnitude of the larger force.

### Example

A force of 5 N acts to the right, and a force of 3 N acts to the left. Calculate the resultant force.

5 N - 3 N = 2 N to the right

### Inertia - Higher

The tendency of an object to continue in its current state (at rest or in uniform motion) is called . Inertial mass is defined as the ratio of force over acceleration. Inertial mass is a measure of how difficult it is to change the velocity of an object.