Maybe I’m being whooshed because I still don’t get this.
Imagine a limo that’s 50ft long. At the back is a standard magnet, North pointing backwards. At the front is a standard magnet, North pointing forwards. I’m about to hit the back of the limo with my North-pointing-forward front bumper.
My car experiences no net magnetic force? :dubious:
Bit of a hijack but why aren’t cars fitted with really thick rubber / springs / whatever for the most likely collisions (yes, like bumper cars)?
I got thinking about this when watching a police-chase-stop type programme, watching yet another police car get damaged by doing a routine (?) pitting maneuver.
How long has this idea been around? I remember that my sixth-grade science teacher suggested it in the early 1970s. He didn’t mention a source, but it probably wasn’t original with him. My reaction then, which I did not share with him, was that a system that would repulse front-end collisions would greatly encourage rear-end collisions.
How about mounting a rail cannon at the top of every car, and when the computers decide collision is imminent the two cars fire 30 lb iron balls at each other. The momentum of firing the balls cancels the motion of the impending impact, and the iron balls collide with one another harmlessly.
It’s the sudden stopping that hurts you, though, whether it’s caused by whacking into another vehicle or by the recoil of firing a cannon. If you want to avoid harm you need a way to slow down more gradually.
Ah, yeah certainly there are arrangements of magnets on a car which produce an external force . . . these won’t lead to magnetic monopoles though.
But as far as magnetic fields as a safety mechanism, like I said it won’t do much good if you’re just using the magnets to bring yourself suddenly to a halt. You need to find a way to slow yourself more gradually, which as Chronos pointed out would require a very long-ranged force.
Instead of discussing the possibility of using magnets around cars, why not go all out and have cars with shields as in Star Trek, so if we see an accident is imminent, we could do like Picard and yell “Shields Up”.
It only cancels out if they’re arranged spherically. In the case you mention, there would indeed be a repulsion against direct collisions, but if the angles are even slightly off of a direct collision, then the cars would probably twist around so that the other car would hit your limo on the side near the back end, where the south pole of that magnet is.
I don’t think this is really fair to the OP. The OP is at least grounded in known science, even if it wont work as described. Finding this out was the whole point of asking the question.
I’d guess these are the real answers - aside from all the other practical considerations like cost and bits of metal being very attracted to the car, the only way to prevent damage to people and cars is to have the “collision” occur slowly enough, and with standard car speeds that implies pretty large effective distances (probably in the order of 50 meters or more), and shrinking the “cushion zone” by any means will only increase the decelleration and hence the potential damage.
Just to clarify, it is still the case that, no matter how the magnets are arranged, one cannot arrange ordinary (non-monopolar) magnets to produce an object that has a net “external magnetic charge”, right? [I’m not sure what I said makes sense, but if something like it is relevant and makes sense, let me know…]
One of the “Danny Dunn” juvenile science-fiction books mentions this exact premise. It was probably the first in the series (Danny Dunn and the Anti-Gravity Paint, 1956), but I couldn’t swear to it. In it, the title character’s scientist friend accidentally discovers a room-temperature superconductor/permanent magnet, and Danny speculates it could be used as car bumpers to prevent collisions. Danny’s friend Joe figures something would go wrong and you’d end with thousands of cars stuck end-to-end.
Personally, I think you’d be better off with LIDAR or SONAR systems that would sense an imminent collision and automatically apply the brakes to reduce impact force. The tech to do this is already in its early stages and as the population ages and the number of senior drivers (with their decreased eyesight and reflexes) increases, I can even imagine such tech becoming mandatory.
I think the main point is that shields (magnetic or otherwise) do not protect the occupants from the forces being exerted on them, or the car for that matter. If the magnets are on the bumper, the bumper will still get bent. If the shield is projected from the frame, the frame will bear the forces. And if the frame is rigid, then the occupants will still experience the forces.
That was my initial objection. The answer seems to be that you have more time to decelerate so it is more like hitting the brakes and less like hitting a wall.