Homework Help: Car safety project help

1. Jan 23, 2005

theknownothing

Hi guys this is my first post and I need some help with this car saftey project I'm doing in my physics class.

I was wondering, hypothetically speaking, if my car design had sensors all around the car that calculated force on impact and it sent it to a computer chip located in the seatbelt area that could calculate the most beneficial time to increase before the seatbelt locks up to minimize force would this even be possible or even sound right?

Lastly, if so the force on impact would just be the mass * acceleration right before impact correct?

2. Jan 23, 2005

Sirus

Welcome.

The most beneficial time to increase what? Systems that sense imminent collisions are already extensively used on higher-end automobiles.

The net instantaneous force acting on any object will be its mass mutliplied by its instantaneous acceleration.

3. Jan 23, 2005

theknownothing

sorry, I meant the most optimal time to increase time minimizing the force on the person.

4. Jan 23, 2005

theknownothing

bump

123456

5. Jan 24, 2005

Sirus

You still need to be more specific. Increase time for what? How does delaying luckup minimize force? Please explain exactly what you mean.

6. Jan 24, 2005

theknownothing

I thought Ft = fT which is impulse and basically what my teacher said is to keep the passanger as safe as possible. which I am having trouble myself for this explaination also, delaying the time will minimize force? I am not sure how that works.

Further explaination = how does a seatbelt work in physics terms?

Last edited: Jan 24, 2005
7. Jan 24, 2005

Matt.D

Are you trying to say that the sensor should detect the optimum moment the seat belt pretentioners should lock in order to stop the forward momentum of the passenger as safely as possible?

Matt

8. Jan 24, 2005

Sirus

Theknownothing, to minimize the damage done to a person during an accident, you need to minimize the net force acting on the person's body, $F_{net}$. Since

$$F_{net}=ma$$

and mass is constant, you need to minimize the magnitude of the acceleration the person undergoes during the crash. If we assume a certain initial velocity $v_{1}$ and a final velocity $v_{2}$ of zero (these values don't really matter), we can see that the time over which the body is accelerated determines the magnitude of the acceleration, and thus that of the net force:

$$a=\frac{v_{2}-v_{1}}{\Delta t}$$

$$a \propto\,\frac{1}{\Delta t}$$

Since $$F_{net}=ma$$,

$$F_{net}\propto\,\frac{1}{\Delta t}$$

Hope that helps.