viking97 said:
if i sit in the front i do, in the back i don't bother.
I remember I was taught this when I did the introductory traffic course: If you sit in the back, using the seatbelt is even more important than when you're in the front. Why? Because the people in the front seat probably appreciate not having a grown person flying towards the back of their seat at 80 km/h.
Let's say you're driving at 27 m/s (that's 97,2 km/h(approx. 60 mph)) and you weigh 100 kg (200 pounds)(for convenience).
In the event of a car crash you will keep moving forward as the car stops. Let's say your impact with the front seat lasts for 0.5 seconds.
That gives you a negative acceleration of 54 m/s^2
F=ma, which gives us F=100kg*54m/s^2 That's 5400 N.
This means the force your body works on the front seat is 550 times the one your weight currently works on the ground.
Imagine stacking 550 clones of yourself on top of that car seat (The car would have to stand vertically of course). Do you think the seat would break?
I imagine the person sitting in the front seat wouldn't be very comfortable.
Edit: Yeah, seems I did some mistakes with the maths and some unreasonable estimates here. Let's say the stop takes shorter time. 0.2 seconds for instance. That equals approx. 138 m/s^2 which is 14 g. 550 g was a ridiculous estimate.
The force you're subjected to is more like 13800 N in this scenario though, it would seem.
Of course, it might be that I've got my maths wrong right now. In any case, sitting in the back seat doesn't mean you're much safer.