Newton's Laws


Newton's First Law

Newton's First Law: If the Resultant Force on a stationary object is zero, the object will remain stationary. If the Resultant Force on a moving object is zero, it will just carry on moving at the same Velocity.

For example, if a stationary Car had a Resultant Force of 0, the Car would not move anywhere so, therefore, staying stationary however if a moving car had a Resultant Force of 0, the car would just remain travelling at the same Speed and Direction otherwise known as Velocity.

When an object is travelling at Constant Velocity it means the Resistive and Driving Forces must all be balanced with each other since Velocity will only change if there is a Resultant Force acting on the object. 

A Resultant Force will always produce Acceleration or Deceleration in the direction of the force and this Acceleration can take 5 different forms: Starting, Stopping, Speeding Up, Slowing Down and Changing Direction. On a free body diagram, this would be represented through unequal arrows.

1 of 3

Newton's Second Law

Newton's Second Law: Resultant Force = Mass x Acceleration 

Resultant Force = N

Mass = Kg

Acceleration = m/s

The larger the Resultant Force acting on an object, the more the object will Accelerate since the Force and Acceleration are Directly Proportional.

Acceleration is also Inversely Proportional to the object's Mass, therefore an object with a larger Mass will Accelerate less than one with a smaller Mass (both with a fixed Resultant Force).

2 of 3

Newton's Third Law

Newton's Third Law: When two objects interact, the Forces they exert on each other are equal but opposite.

For example, if you push a shopping trolley, the trolley will push back against you with the exact same Force. However, as soon as you stop pushing the trolley, the trolley will also stop pushing against you.

Another example is in an Equilibrium situation where a man is pushing against a wall. As the man pushes the wall, there is a normal Contact Force acting back on him and these two Forces are equal to each other since they are the same size. As the man applies the Force by pushing the wall, the wall metaphorically pushes back on him with the same size Force.

3 of 3


No comments have yet been made

Similar Physics resources:

See all Physics resources »See all Forces resources »