Science Project Help

[matthewdaye]

I was wondering if anyone had any information about the forces in a car crash at different speeds. I am also looking to find info about how much force opposing magnets can have on each other. I am trying to figure out how big of a magnet you would need to have in two cars if they crashed to signifigantly increase the chance of survival... I know it sounds crazy, but we get a lot of points for creativity in this project

[ed84c]

F=ma

 

calculate the compressing speeds of different helmet fomes.

 

Alternativley throw an action man at a wall.

[5614]

f = ma

 

where:

f = force

m= mass

a = acceleration

(just in case you didnt know that)

 

also it makes a very big difference between say stopping quickly and stopping dead still... if you are going from even a small speed to dead still then it is suprising violent... i mean really suprisingly violent.

 

the english police (i have seen this in a few places) set up a little cart thingy that you sit on, it goes down a ramp which is say 1meter high and goes on for a few meters, at the end it stops dead... when it hits that end whoever is on it goes shooting off it! not far, but will come clear off it... and that is at such a small speed.

 

are you looking at more depth into the forces in crashes... the forces in varying speed crashes...

 

what do you mean about the magnets?

do you mean two magnets to repel the two cars away from each other?

[Klaynos]

As 5614 said about the violentness of stoping suddenly I thought I'd just quantify that a bit.

 

Impulse = new momentul - original momentum = Force * change in time

 

(Force=rate of change of momentum)

 

This can also be written as

 

Impulse = intergral between t1 and t2 of the sum of F dt

 

Although that is superfluse for your understanging of it.

 

So going back to Impulse = new momentul - original momentum = Force * change in time, the momentul change is constant due to the conservation of momentum, so if the time is decreased to maintain this conservation law the force has to get considerably bigger.

 

This is why cars have crumple zones.

[matthewdaye]

You guys really have in depth answers. I did mean two negative magnets by the way, so the cars would repel each other. I wonder if anyone has any equations or info about how much force two magnets have when opposing each other. If this idea goes no where I was going to change my idea for my project to something like how we could use animal traits or abilities for our benefit. Maybe something like Biosteel where they put the spider genes in the goat milk or whatever. Something along those lines. Any ideas? The car crash idea would be my main pick tho

[matthewdaye]

I forgot to ask something. I know I sound stupid but thats why im asking. What unit is the force in, in the equation f=ma...? also would the acceleration be mph or kph? also the mass is it in tonnes, pounds?

[5614]

force = = N =netwons

mass = KG = kilograms

acceleration = m/s^2 = meters per second squared = (change in speed)/t

 

so if you started at 0meters per second and ended up at 5meters per second within 5 seconds and had a mass of 50kg

 

then acceleration = 5/5 = 1

mass = 50

therefore:

f = ma

f = 50 * 1

f = 50 newtons

[Klaynos]

I'm afraid I don't know any normal magnet formulae for repulcive forces, never even come accross any, if noone get's back to you I'll try and have a look about and quiz my friends tomorrow afternoon, sorry I can't investigate now got an exam in the morning

[bishnu]

In standard ("american" units) the units for force would be pounds, acceleration would be feet per sec^2(this could be converted to mph^2 i you so desire) and the mass would be in slugs(you can ge the weight in slugs by dividing how many pounds it is by gravity's acceleration 32ft/s^2).

 

The best equation you can use is impusle Force*time=change in momentum(momentum is mass times velocity)

 

A much easier approach would be to find the kinetic energy of the cars and find out how much work the magnets have to do agaisnt each other.

 

Magnatism is a weird force. The only difference between the electic force and the magnetic force is that the magnetic force is only generated while moving.

 

Force magnetic=(charge of the particle)(velcotiy)(strength of the magnetic field)(sin(the amount of degrees between the direction of the velocity and magnetic field)))

 

Now i am not sure aboutthis, but i assume that the magneitc field decays at 1/(distance)^2 and i not it will probably give you a decent apporixamtion.

 

 

OKay the force =(charge)(velocity)(strength of the magnetic field/) since force equals m*a you get(im going to do it symbolic from now on becaus it will take too long with out it)a=(q/m)(v)(Bi/(2x)^2) this is a differental equation(i am assuming that the other car is going the exact same speed and both exert the exact same forc eon each other). Now solving this equation you get(on second thought this equation might not be solvable in any useful way)...oh well mathematica cant solve it so im going to go with scrap the 1/(2x^2) because it makes it non-linear so we can go with that the magneitc field is going to be constant thorugh the "trip" so a=(qB)/m*v which equals v=(Vi)exp{q*B/m*t}, now if we intergrate to get the distance it travels during that time we get x=(Vi*m/qB)(exp{q*b/m*t}-1) now by solving the first equation for time we can then find the distance it travels before it stops(except by using our model it will never stop it will approach zero as it goes toward infinity so you are going to have say that a certain small vaule is going to be zero) and then find the distance it travels.

 

But i think that you would probably want to use the electric force more to get the cars to stop in which case it would be x=K_cQ1*Q2/(m_car)(v)^2

 

oh BTW vi=velocity intial B=magnetic feild strength q=charge m=mass K_c=columbs constant 8.99E9 i belive i could be wrong t=time

[matthewdaye]

I need some examples, but I really thank you guys for your help. I was thinking along the lines of 50, 80 and 100 kph whatever that is in feet per second. I was also thinking about how if i used an electromagnet it would eliminate the possibility of cars accidentally sticking together and it would turn on like airbags when a mechanism was touched or compressed.

[5614]

well a problem would be getting all cars to be fitted with this device... that is if it were properly designed and worked well in the first place.

 

youd need a decent power source for a starter.

 

also, as always, you must remember the cost vs benefit ratio.

 

i was watching a program on flight safety, there are some critical flight safety features that could have saved hundreds of lives except they didnt put it in because it was not worth it for them... even knowing that hundreds had died, it still worked out cheaper for the airline not to include this safety.... now there are so many of hundreds of flights it is worth it, that case was from a few years ago when flight travel was less common.

[YT2095]

I was thinking along the lines of 50, 80 and 100 kph whatever that is in feet per second. I was also thinking about how if i used an electromagnet it would eliminate the possibility of cars accidentally sticking together and it would turn on like airbags when a mechanism was touched or compressed.

 

any magnet powerfull enough to repel cars at that speed and mass, would severely mess up a whole load of other things too!

[matthewdaye]

Ok, the things said will be good for the cons part of my project but I wonder If anyone can help with the equation to show the math behind it. I pretty much knew at the first that it would not be feasable in real life.

[matthewdaye]

P.s. man this site is informational.... have to come here more often

[5614]

YT2095 has a website, on it it tells people that this is a good site but "still wont do your homework for you"!

 

i personally do not know what equation you are looking for however it will vary with every type of magnet (like neodiyum iron boron compared to an ordinary iron magnet) also the size will matter greatly... for electromagnets it'd depends on the voltage, current, number of coils, size of coils and the center.

 

as nothing like what you have described exists, like magnets repelling things as a way of decleration or breaking i dont know if anyone has found an equation for it yet.

[matthewdaye]

I knew I was pushing my luck, should have been satisfied with the info you guys gave me. It was good stuff after all. But what I really wanted was help with the force equations, I will try first but i'm only in grade 11 and they are a little hard for me. I am trying right now to find out how strong electromagnets can be. I found out about the coils and volts and stuff you were talking about. Seems like thats what I will go with. But please don't think of me as ignorant, I really am trying to figure it out on my own first. Thats the only way someone can learn, right? But if anyone does have any helpful information or knows someone that does please dont be hesitant to e-mail me at dayej2@student.ednet.ns.ca or phantom_ellipsis@hotmail.com. If if helps, I was thinking of a magnet weight that would not hinder the car greatly. Possibly 250-300 lbs? Maybe higher. I was also thinking about putting them on the sides for side on crashes. Also, I have a question, do you think the magnet would shatter after being struck. I have read that neodymiun magnets can be quite brittle, not sure about electro. I also just want to remind that I'm not looking for something that is going to bring the cars to a stop, just slow them down maybe by half the speed.

Thanks Everyone

[coquina]

You might want to contact someone here and ask your question:

http://education.jlab.org/

 

There is an email address at the bottom of the page. I do machine shop work for these people - it is a continuous beam electron facility. They use extremely powerful magnets there.

 

One of there scientists brought me one of their magnets in which he wanted a hole drilled. Magnets are manufactured by "sintering" the iron powder is pressed into shape. When we tried to drill the hole, the magnet's strength would not allow the chips to come out, so it didn't work.

 

Anyway - here is another site where you can buy small very powerful magnets.

http://www.amazingmagnets.com/products.asp?ID=1000-10&GAWNRE

 

Maybe you could use two radio operated model cars and install a magnet on each one and test your theory.

 

The magnetic field might well mess up the radio waves that control the cars, I would also think that super magnets might damage a full size car's engine or its electrical source.

 

However - I do know that a similar technology is used in "Maglev" trains. Read about them here.

http://travel.howstuffworks.com/maglev-train.htm

[5614]

neodymiun magnets

stronger than neodiyum magnets are a composition of neodiyum, iron and boron or NIB magnets... they are the most powerful permament magnet discovered.

 

and yes they are VERY brittle, they can break from the attractive force between 2 of them alone... and i speak from experience when i say that i had two NIB magnets about 1cm across and 0.5cm high, i had for of them and one of them snapped in half somehow, i was not aware of it happening and just found it like that, it didnt look it, i was just pulling them apart and notice it was in two pieces, it is my assumption that it happened when i just let them "snap" together.

 

I also just want to remind that I'm not looking for something that is going to bring the cars to a stop, just slow them down maybe by half the speed.

a magnet would make a difference, especially a powerful one, but as YT said it'd also screw up a lot of other things.

[matthewdaye]

Just wanted to thank everyone for their help, I passed in the project today. Hope I get a good mark. I found some formulas for electromagnets that seemed to work pretty good and the force equations you all posted worked good too. I will post the website for the formulas. This is not the same one I used, I can not seem to find it but here is one that is similar http://physics.villanova.edu/faculty/shaw/lab/magnet.htm <---in case anyone needs it.....