Crumple Zones on Cars

  • Thread starter physium
  • Start date
  • #1
1
0

Main Question or Discussion Point

How do crumble zones on cars work in relation to Newton's 2nd Law (F=ma)?
 

Answers and Replies

  • #2
110
2
They work by reducing the "a" in F = ma.

If you are moving in your car with velocity v, and you have to slow down to 0 over a distance of L, then you will experience an (average) acceleration of

a = v^2 / 2L

If you assume that you collide with a really hard body that is not deformed at all during the collision, then L is identical with the length of your crumble zone. So the acceleration you experience is inversely proportional to the length of your crumble zone.
 
Last edited:
  • #3
35
1
How do crumble zones on cars work in relation to Newton's 2nd Law (F=ma)?
You can think of this in terms of reducing the momentum (P) of the car to zero. The change in momentum is called Impulse (J) and we can write its magnitude as:

J = (average force) F * (time) T.

This is derived from Newton's second law in the form F = dP/dt.
So for a given J we can reduce F by increasing T. This is what the crumple zone does.
 

Related Threads for: Crumple Zones on Cars

  • Last Post
Replies
1
Views
6K
Replies
2
Views
4K
  • Last Post
Replies
2
Views
4K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
1
Views
856
  • Last Post
Replies
1
Views
1K
Replies
5
Views
919
  • Last Post
Replies
1
Views
2K
Top