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Question of the Week episode

Sun, 20th May 2012

Can a magnet be so powerful it crushes what it attracts?

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We apply some Naked Science force to this week’s question by finding out if we can we make a magnet so strong that is squashes, rather thanks sticks to, your white goods. Plus we ask do motorways create a microclimate?

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Depending on what you mean by 'crush'- there was an embarrassing case I heard about where a superconducting magnet intended for a particle accelerator mechanically failed when they established the magnetic field. Magnetic pressures are quite high, about 50 tonnes per square metre (5 atmospheres), and crushing things is perfectly possible, if rare. But it's too weak to crush solid materials, it would only destroy things if they're fairly thin and holding larger, thicker magnetic objects. wolfekeeper, Tue, 22nd May 2012

I have no doubt that a strong magnet could crush a small sheet metal container.

However, the magnetic field strength falls off with the cube of the distance.  So, for example, in a wrecking yard that uses a magnet to move cars, the magnet doesn't crush the car by the strength of magnetic pull because when you would attach to the roof of the car, the frame would be several feet away, and experience a much weaker magnetic field. CliffordK, Tue, 22nd May 2012

To be strictly accurate, magnetism is a 'near field'. With near fields the drop off in field with distance depends on the shape of the object generating it, although as the distance increases it does usually go as inverse cube (for dipoles), but can die away more quickly with quadrupole fields and such like. wolfekeeper, Tue, 22nd May 2012

Maybe not in Oxford ... RD, Fri, 25th May 2012

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