# Why we wear seat belts in terms of momentum?

1. Oct 25, 2004

### Gughanath

can someone please explain why we wear seatbelts in terms of momentum?

2. Oct 25, 2004

### arildno

Basically, you have two other options:
1) No seat belt.
When the car suffers a collision, you still have the velocity the car had.
Hence, you'd fly forwards through your front window..
Would you like that?
2)Seat belt/rod fastened to the car, but made of iron (or some other inflexible material).
In this case, you are forced to decelerate to zero as fast as the car does.
The rod would slice you through (a BIG force acting on you).
Not nice, IMO.

The seat belt allows you some longer time than in 2) to decelerate to zero, hence
the force acting on you will not be that great.

3. Oct 25, 2004

### Gughanath

oh ok..i understand it now....
but how does wearing trainer in a run help run better in terms of momentum??

4. Oct 25, 2004

### Gughanath

does it reduce the time taken to get from one point to another hence, increasing the force with which we run??

5. Oct 25, 2004

### arildno

Since I'm Norwegian, there's quite a few English words I don't know so well..
Is "trainer" a tight-fightting suit? (or "condom suit" as we call it in Norway..)

6. Oct 25, 2004

### Gughanath

hahahaha....lol....em.....trainers are sports shoes...shoes that we wear when we run in a track or play inside a gym

7. Oct 25, 2004

### arildno

Oh dear..

8. Oct 25, 2004

### Gughanath

sorry....have i confused you??

9. Oct 25, 2004

### arildno

As for the sport shoe, it works a bit like a spring; when your foot compresses it, some of the kinetic energy gets stored in the shoe, rather disappearing from you as when your foot strikes the ground.
In the upwards movement that stored energy aids you; you don't have to exercise that much force yourself to run at a given velocity as what you'de had to do if you were running bare-footed.