1.21

1.21 use the ideas of momentum to explain safety features

Example

Explain how motorcycle and bicycle helmets can protect their users during a collision

 

Answer

·         Helmet or bare head, the change in momentum of your head during a collision is equal

·         With a helmet, this change in momentum takes place over a longer time

·         This means that the force needed to change the momentum of your head is less

or use the equation

·         Impulse = Δp = F x t where Δp = constant

·         cushioning in helmet => increases t

·         and therefore decreases F

 

 

1.21 Plenary answers

13 March 2012

15:20

Physics for You p.147 Q2c

2c. Why is the front of a car designed to collapse in a serious collision? (3 marks)

 

·         There is a force when you crash that decelerates the car (decreases your momentum)

·         If the front of the car collapses (this is the crumple zone), this force acts for a longer time than if the front of the car were rigid

·         This means that the force needed to change the car's momentum is less and there's less risk of injury to the driver

or use the equation

·         Impulse = Δp = F x t where Δp = constant

·         crumple zone increases t

·         and therefore decreases F