1. Christmas Car Crash Lecture: Road Safety
08 June 2019
Objective
To understand how kinetic energy can help to explain dangers on the roads and how a knowledge of momentum has helped to minimise the impact of crashes.

2. Outcomes
ALL MUST understand the factors that affect kinetic energy and why the speed a vehicle travels at is much more important than what it weighs.
MOST SHOULD be able to describe what momentum is and what happens to the impact force if the time for the impact is greater.
SOME COULD explain why the impact force changes when the time for the impact is greater.

3. ad

4. Volunteers
faces

5. Collisions There are two things we need to look at in a collision:
The Momentum and Impact Force
And The Energy in the collision.

6. twice the energy – twice the hurt!!
Kinetic energy
Mass or Speed?
KE=1/2 m v2,
e.g:
½ = 500 J
½ = 1000 J
twice the energy – twice the hurt!!
Mass (doubles)
Kinetic Energy (doubles)

7. So if you double the mass so does the amount of KE you have.

8. 4 times the energy – 4 times the hurt!!!!
But if your speed doubles the amount of kinetic energy goes up by 4 because;
KE=1/2 m v2
e.g:
½ = 500 J
½ = 2000 J
4 times the energy – 4 times the hurt!!!!
Velocity (doubles)
Kinetic Energy (quadruples)

9. So if you double the speed you quadruple the KE you have.

10. Demo dropping stuff on faces and jelly…

11. demo

13. Momentum
What is momentum?
Volunteer
Skateboard
….gun

14. MOMENTUM = MASS X VELOCITY
What is momentum?
Ping pong ball
Medicine ball
MOMENTUM = MASS X VELOCITY

15. Impact Force
If we are in a crash how do car manufacturers help to reduce the impact?
Seatbelts
Airbags
Crumple zones

16. Impact Force
If we are in a crash how do car manufacturers help to reduce the impact?
Seatbelts
Airbags
Crumple zones

17. Impact Force
If we are in a crash how do car manufacturers help to reduce the impact?
Seatbelts
Airbags
Crumple zones

18. What do seatbelts, airbags and crumple zones do?
They all increase the time that a collision takes place and so reduce the impact force.

19. Volunteers please – 1 to start – catching a cricket ball
3 more please
Eggs….

20. Impact Force Impact Force = change in momentum time for impact
Impact Force is the Rate of change of Momentum
Impact Force = change in momentum
time for impact
e.g: 10 = 5 Newtons 2
10 = 1 Newton 10
Impact Force
(gets smaller)
Time of impact (gets bigger)

21. Change in momentum and impact force
When the change in momentum is the same but the time over which it happens gets bigger, the Impact Force gets smaller.
The bigger the contact time in a collision, the less it hurts!!!!

22. Comparing safety features

23. Plenary What 2 factors affect kinetic energy?
Explain why the speed a vehicle travels is more important than what it weighs when describing how safe it is on the road.
What is momentum?
What happens to the impact force if the time for the impact is greater?
Explain why the impact force changes when the time for the impact is greater.