4.1.16

# Newton's Laws

Test yourself

## Newton’s 1st Law

Newton's 1st Law says that the velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary (still) or moving object.

### Stationary (still)

• If an object is stationary (not moving) and there is no resultant force acting on it, it will stay stationary.

### Moving

• If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed.
• This means that the object will continue moving at the same velocity.
• This also means that the velocity of an object will only change if a resultant force is acting on the object.

## Newton's 2nd Law

A force may cause a mass to accelerate. This acceleration can be a change in speed, a change in direction or a change in both speed and direction. This is Newton's 2nd Law.

### Resultant force

• The resultant force is the sum of all of the forces acting on an object.
• The change in an object’s motion is caused by the resultant force.
• If the forces acting on an object are unbalanced (not equal) it means that a resultant force is acting on the object.

### Resultant force equation

• A resultant force causes an acceleration.
• The acceleration can be calculated with this equation.
• Resultant force (F) = mass (m) x acceleration (a).
• This is Newton's 2nd Law.
• Remember that the resultant force is the vector sum of all forces. You need to take into account their directions.