Any suggestion for a car safety physics project?

[vycanismjrs]

hey I'm a high school student which majors in science (physics) and to pass my grade i need to make an essay paper including the problem, experiments, and of course conclusion. But I can't make up my mind of what topic should I make. And one thing that gave me an idea is about car safety, does a safety belt really save you in an accident or does the shape or position could harm you in a large impact. Any suggestion of what should I make? The problems and possibly how should I do the experiment with because I ain't going to crash my car for the experiment, is there any easier way to test this?thankyou so much if you're willing to help :) ps: or maybe about the car's centre of gravity and how it effects the safety of it in a crash.

 

[Simon Bridge]

Welcome to PF.
You can do experiments on models.
You don't have to actually crash your car to do safety experiments either... car safety is not just about collisions. What about loose objects in a car? (Mythbusters did a large-scale one of this) or maybe you can find someone legal age and test: safety vs alcohol consumption (use a videogame car). Compare with the legal limit.
You can also use your car to tow a cart at objects (see the mythbusters episodes).

Center of Mass experiments will be easy to do on models - you can move weights around - but you have to figure what you mean by "safety" in this context.

Seatbelts would be tough - the trouble is working out how to assess the difference between seatbelt injury and an unrestrained crash in the same conditions. You'd need to build a cart with an old car-seat on it and a seatbelt, tow the cart (with some sort of dummy) at an obstacle ... rig something to assess effect on the dummy... find someplace to do the test. Resources you see.

 

[vycanismjrs]

thanks!

the 'car safety' i mentioned on the center of gravity is maybe about the body roll? or when the car crashed which position of the center of gravity will suffer more damage, is it the one in the centre, front or the rear.

and how is the easy way to measure the amount of damage in a model car? so i could know the difference between them.

 

[mrl rao]

Centre of gravity (cg) must lie in the front.The reason: In case of accident if the cg is in the front the car may rotate about the front axle so that part of the kinetic energy is converted into rotation (which may result in decompreession of rear suspension) about the front axle and part is decreased due to friction during rotation.If the cg is at the rear, entire KE will be lost in collission in relatively lesser time resulting in more severe damage. Thus cg at front is preferable.
Regarding seat belt: In the absence of a seat belt the passenger or driver will be held firmly in the seat so that he will not move due to inertia in the forward direction during collission and collide with the vehicles body.
Thus seat belt is must while cg in the front is preferable.

 

[vycanismjrs]

wow thanks I'm started to get my ideas going about this paper.

what is your suggestion about the experiment I may do to test the centre of gravity thing?

And the problem I want to test in seatbelt is about it's position or it's shape because it's relatively thin and smaller areas with bigger force equals bigger pressure and could it damage the passenger's body even more? And how could engineers make it even more safer.

 

[Simon Bridge]

Centre of gravity (cg) must lie in the front.The reason: In case of accident if the cg is in the front the car may rotate about the front axle

... etc. But head-on collisions are not the only kind of accident. What about side, rear or angled collisions? What is the effect on rolling?

In normal operation of a car, it helps to have some weight on each wheel. Putting the COM just behind the front wheels gives you weelbarrow stability and a tendency to flip over forward in collisions because there's nothing to hold the back down. Well done :) But makes a nice experiment about the tradeoffs of different weight distributions.

In small collisions the seatbelt could be worse than the forward shift of the body if it holds you too tightly.

Note - the bits of your body that usually impact the car body in an accident (knees, head) are quite a lot smaller area than the seatbelt - and cover a more brittle area harder to fix if it breaks. That's part of the tradeoff - which bit do you want to get damaged?

You can do a proof of concept test in your own car without crashing - get a friend to drive at speed then slam on the breaks while you are riding shotgun (don't brace) - compare with and without the seatbelt.

After that you really need to use a towed cart - usually just 5-10kmph collision is enough to give you the info you want without doing permanent damage.

What you should do is gather your resources and "play around" with different tests until you get a feel for what is going to happen. Once that happens, the tests you do formally for the project will be obvious and you don't have to tell the teacher about the other ones :)

But if you are really keen on one particular thing to test, then go for it. You will do your best work on the stuff that just nags at you. What you do will be for personal reasons, we cannot advise you on that - just describe the playing-field: you have to pick the position to play.

 

[vycanismjrs]

yeah but experiment is the requirement of this paper and this paper is one of the requirements for me to graduate from high school! that's why I'm freaking out lol

I really interested of the centre of gravity because it seemed reasonably easy for me. But on what thing should I test the different CoG? a model car? Or a remote control car? or is there any other way?

 

[Simon Bridge]

Depends on the experiment - suggest you think about something like the std physics cart and a ramp. Or you can build a frame with four wheels. Needs to support a lead weight. The ramp let's you control the final speed. And it's cheap :)

It's how you control your variables that will count.
You are what level? Think what sort of experiments you've done in class.

You may want to have a look online about how the engine placement in the car affects the handling :) there are front, rear, and mid-engine cars. Remember, it does not have to be great ... just demonstrate your understanding of the scientific process.

Oh, and when you've figured out what you want to do - tell your teacher about it.
You'll probably find the school has resources that you can use, and your teacher will know of what else to do. Teachers love giving advise to keen students who ask :)

 

[vycanismjrs]

great! that'll do :D

and what should I test? the speed? and how could I know the difference in damage or body roll on each car?

btw I'm on my second grade of high school so that explains my shortage of resources T_T

 

[Simon Bridge]

You needn't worry about actual damage - look at stability.
Vehicle safety is about the passenger safety after all ... cars are designed to all-but disintegrate around the humans, so damage is not the issue.

Do you want to know how easily it rolls under different conditions?
Stopping distance would be an interesting test and/or how fast it can corner.
Move the weight around to see how it affects the dynamics.
Make your test rig ans see what it will do.

You can use a sloped track, or build something that runs on rails and pull it with a dropped weight ... all depends on your resources and what sort of tests you want to do. It's wide open.

You should have enough now to try something out and make a decision :)

 

[vycanismjrs]

haha thankyou so much Simon you really helped a lot. Sorry for the questions :p

 

[Simon Bridge]

No worries - when you've done something, take pics, and show us :)