# Car crash pressure.

1. Jun 4, 2005

### Frank_Horrigan

Hello, for a part of my grade 11 physics paper I have to describe how air bags are useful in car crashes. So far what I've done is a sample crash, calculating how much force is on the driver, then i calculated the pressure that would be on the driver. I was wondering how much pressure would be fatal in a car accident, if anyone could point me to a site or something which explains this I would be grateful.

Another question, what would be reasonable area to use for car crashes

With aibag and seatbelt hitting the chest (I said .5m^2)
With onyl seatbelt hitting the chest (I said .025 m^2 (thinking seatbelt covers 5 cm x50 cm of your body))

Last edited: Jun 4, 2005
2. Jun 4, 2005

### brewnog

I'm not an expert here, but I'll set the ball rolling...

I suspect that the amount of energy (rather than pressure) absorbed by the various parts of the occupants of the car is of more use in determining the extent of injury that the occupants suffer. Being subjected to a very high pressure for a very short time can cause less damage to a person than being subjected to a moderate pressure for a longer time, and your investigation should account for this. However, you seem to be getting there...

As for your contact areas, I think that your seat-belt only value is close enough (perhaps a little bit high, especially if you consider non-uniform loading). Your seat-belt and airbag value seems very high though, what type of airbag is this?

3. Jun 4, 2005

### Frank_Horrigan

After thinking about what you said about the air bag I decided to change my size down to .3m^2 which to me seems more reasonable. I don't know what to do about the pressure injury aspect of this problem though, the exact problem says explain how airbags minimize injury during a head on collision using physics diagrams and examples. I'm not sure if this means to explain how much damage was actually done, or if it means to just compare airbags to seatbelts. After thinking the pressure thing through more it seems that the question doesnt really work because I would think that pressure done to your face would result in more damage then the chest area. So there is no numerical value to the amount of pressure probably.

I guess I will just comapre the two and come up with a diagram for it.

4. Jun 4, 2005

### brewnog

Any numerical value of pressure would indeed change rapidly with time over the course of a collision, and (as you say) have different implications for different body parts. If you want to think about numbers, I think that energy transferred to the victim would be a more useful parameter, but I'd like someone else's opinion on this.

For now, I would probably concentrate on looking at the reasons why airbags can help to prevent injury, as compared with seatbelts. You should be thinking about what the effect of cushioning actually is, - reducing the magnitude of deceleration of the victim's head. You could easily have diagrams (and even sketched graphs, with a little imagination) here.