# Magnets to stop car crashes.

by Spikeywan
Tags: crashes, magnets, stop
P: 15,319
 Quote by M_Navas Okay, this is assuming we are trying to PREVENT an accident from ever happening, but if the affect were to be pronounced like bumper to bumper traffic with some drunk guy not noticing that the cars ahead aren't going very fast, the guy sitting in bumper to bumper traffic is going 4.2 meters per second, ... having magnets do the job is a BAD idea
You know, I hadn't thought of that. In heavy high-speed traffic, cars will be pushing off each other like bumper cars. Anytime there is an imbalance in speeds, so that cars don't stay at a constant distance, you would, at best, be nudging the car ahead of you and/or being nudged by the car behind you.

This is extremely dangerous.
 P: 146 Would it be possible to absorb some of the kinetic energy of before impact by using electromagnetic induction? If the colliding system could act like a transducer, could one car convert some of the kinetic energy into electrical energy using some type of solenoid configuration?
P: 15,319
 Quote by GRB 080319B Would it be possible to absorb some of the kinetic energy of before impact by using electromagnetic induction? If the colliding system could act like a transducer, could one car convert some of the kinetic energy into electrical energy using some type of solenoid configuration?
You want to invent regenerative collisions???

Are we having so many accidents that you figure it's viable to extract energy from them?
Mentor
P: 22,284
Slight clarification:
 Quote by DaveC426913 a] slowing the car over time, even milliseconds (much longer time than an impact) will dramatically lessen the damage (I can push on a wall and it will resist, but if I apply the same force over a shorter time (say, punch it), the wall will simply fail).[emphasis added]
That should be same impulse (force*time) or momentum change. Obvoiusly, the force of a fast impact is vastly larger than the force of a slow impact. Consider getting hit in the head by a golf ball or nerf football of the same mass - being softer, the nerf football deforms and takes longer to decelerate, reducing the force.
Mentor
P: 22,284
 Quote by DaveC426913 You know, I hadn't thought of that. In heavy high-speed traffic, cars will be pushing off each other like bumper cars. Anytime there is an imbalance in speeds, so that cars don't stay at a constant distance, you would, at best, be nudging the car ahead of you and/or being nudged by the car behind you. This is extremely dangerous.
Meh - it would just force you to maintain safe following distance. To be effecive, these magnets would only need to have a substantial effect at a distance of perhaps 5-10 feet.
P: 15,319
 Quote by russ_watters Meh - it would just force you to maintain safe following distance.
I agree. The trouble is, several feet of your car, both in front and behind, are invisible. "Keeping a safe distance" becomes many times harder when you can't tell where your car ends.

You just know that cars are going to be bumping off each other all the time. And that makes a big safety/control hazard.
P: 10
 Quote by DaveC426913 You know, I hadn't thought of that. In heavy high-speed traffic, cars will be pushing off each other like bumper cars. Anytime there is an imbalance in speeds, so that cars don't stay at a constant distance, you would, at best, be nudging the car ahead of you and/or being nudged by the car behind you.
Ya and you cant forget about the cars to the sides of you as well, it is not just about maintaining distance from the car ahead of you, but if someone goes to pass you in the lane next to you the magnetic repulsion could push both cars off the road, and you said it best:
 Quote by DaveC426913 This is extremely dangerous.
 P: 2,292 Ok, my humble thoughts... "Magnetic Bumpers" would not work in real-life, full-scale vehicles. Too expensive, the effect is short range, all vehicles would have to be so-equipped, serious added vehicle weight, etc... The negatives FAR outweigh any positives.
P: 2,050
 Quote by xxChrisxx You can think of it as an invisible inflatable cushion in front of your bumper.
Now there's a great idea!

Have additional, external airbags that trigger if the front of the car is a metre from any (excessively) rapidly approaching obstacle (where excessively is defined in relation to the capability of the vehicle's brakes). That sounds trivial to implement, just enhancing a parking range-finding system to account for Doppler effect. Bonus: potential for reduced pedestrian harm. (Potentially reduced panel-beating expenses for both vehicles in rear-end collisions.) What do people think?
P: 10
 Quote by cesiumfrog Now there's a great idea! Have additional, external airbags that trigger if the front of the car is a metre from any (excessively) rapidly approaching obstacle (where excessively is defined in relation to the capability of the vehicle's brakes). That sounds trivial to implement, just enhancing a parking range-finding system to account for Doppler effect. Bonus: potential for reduced pedestrian harm. (Potentially reduced panel-beating expenses for both vehicles in rear-end collisions.) What do people think?
Here is what I posted earlier, it is much more practical then using magnets and would be lower cost as well...

 Quote by M_Navas IE a sensor you can turn on and off at will that, upon having an object enter its sensory area deploys an air bag off of the bumper that slows the "infiltrating" object down before impact...
 P: 2,292 Indeed, a bumper air-bag would be far superior in cost AND effectiveness versus a magnetic arrangement... in my opinion.
 Mentor P: 16,317 I'm trying to imagine parallel parking with such magnets. It would be....exciting.
P: 10
 Quote by Vanadium 50 I'm trying to imagine parallel parking with such magnets. It would be....exciting.
you just gun it and the other cars will automatically move out of your way :P
P: 2,050
 Quote by M_Navas you just gun it and the other cars will automatically move out of your way :P
If they're that strong, you're going to have to start worrying about polarity, whether they flip over and attract crushingly. Go with external airbags.

 Quote by M_Navas I posted earlier
Might have missed the edit. Anyway, you do want to use doppler range+rate-finders to trigger the external airbag deployment. Not something that depends on being switched on (by a driver whose negligence and human-error is already in issue), and not something triggered solely by range (since unnecessary deployment is expensive: interior airbags already cost ~\$2000ea to replace).

External airbags might be the opposite of SUVs: any potential safety improvement is shared with, rather than wholly at the expense of, the other party.
 P: 10 Nah you did not miss the edit, in the edit I just changed the terminology from CAR to INFILTRATING OBJECT because I realized you wouldnt have to use it for just cars
 P: 10 also, I am aware there would need to be more factors in the airbag and not just having an object in a sensor but I don't really feel like getting into that lol and for the doppler it would need to be something relatively sensitive due to cars like the prius not making much sound at all when they drive
P: 146
 Quote by DaveC426913 You want to invent regenerative collisions???
My question was whether or not it would be physically possible to design such a system; I have no aspirations to invent such a system.

 Quote by DaveC426913 Are we having so many accidents that you figure it's viable to extract energy from them?
My question was whether or not it would be physically possible to design such a system, not whether or not it would be a viable option.
 P: 15,319 You know, I just thought of another giant flaw in the magnetic bumpers concept: For every repulsive interaction, there is going to be an attractive interaction somewhere else. Say you give all cars powerful N-poles on their front and rear bumpers. Great. All cars repel each other as long as they are oriented bumper-to-bumper. But those magnets also have S-poles. One car approaching another from the side will actually be attracted, worsening side-impact accidents!

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