# Force and Impulse

This states that the force is a measure of change of momentum with respect to time. This is Newton’s Second Law of Motion:

The rate of change of an object’s linear momentum is directly proportional to the resultant external force. The change in the momentum takes place in the direction of the force.

If we have a trolley and we increase its velocity from rest to 3m/s in 10 seconds, we know that it takes a bigger force to do the same with a trolley that’s full of shopping. Ever tried turning a trolley around a corner when empty and then when full?

Force is measured in Newtons, N

# Car Safety (Also seen in GCSE Physics 2)

Many of the safety features of a car rely on the above equation. Airbags, seatbelts and the crumple zone increase the time taken for the car and the people inside to stop moving. Increasing the time taken to change the momentum to zero reduces the force experienced.

# Catching

An Egg: If we held our hand out and didn’t move it the egg would smash. The change in momentum happens in a short time, making the force large. If we cup the egg and move our hands down as we catch it we make it take longer to come to a complete stop. Increasing the time taken decreases the force and the egg remains intact.

Cricket Ball: If we didn’t move our hands it would hurt when the ball stopped in our hands. If we make it take longer to stop we reduce the force on our hands from the ball.