# 5.9.4 Force & Momentum

Higher Tier Only

### Force & Momentum

• When a force acts on an object that is moving, or able to move, the object will accelerate (or decelerate)
• This causes a change in momentum
• More specifically, the force is the rate of change in momentum • Δt is the change in time, or the time taken for the force to change
• Where the change in momentum is defined as

Final momentum – Initial momentum

• Force and momentum are vectors so they can be either positive or negative values

#### Exam Tip

Maths Tip: Remember ‘rate of change’ describes how one variable changes with respect to another

In maths, how fast something changes with time is represented as dividing by Δt (e.g. acceleration is the rate of change in velocity)

More specifically, Δt is used for finite and quantifiable changes such as the difference in time between two events Higher Tier Only

### Calculating Force & Momentum

• The force and momentum equation can be derived from Newton’s Second law and the definition of acceleration #### Worked Example

A tennis ball hits a racket with a change in momentum of 0.5 kg m/s.

For the different contact times, which tennis racket experiences more force from the tennis ball?  ### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
Close Close