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KillerCodeMonky t1_j8ia5jn wrote

Reply to comment by KrombopulosThe2nd in Light traveling through a medium that slows it. Does the same photon emerge? by TheGandPTurtle

Yes of course these are not perfect processes. Otherwise an undersea earthquake would create a tsunami on all of its coastlines. Energy is lost or made non-coherent in a variety of imperfections, including heat and scattering. In the case of ocean waves, they are typically created and recharged by the wind as they move along.

I mostly wanted to make the point that a wave is not displacing its medium, but simply moving through it. A wave is nothing but water and energy. There's nothing there displacing the water to do work. The water moves around due to the energy, but in a way which is generally neutral in terms of work actually done. A wave hitting the shoreline really just transfers from moving through the water to moving through the land.

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DamionFury t1_j8ijw6m wrote

Work can turn out to be one of the less intuitive aspects of physics. For example, magnetic fields cannot do any work because they act orthogonally to the direction of motion, yet it certainly looks like work when you use an electromagnet to lift an object and make it float. I wish I could remember the explanation my Electromagnetism professor gave me for what is actually doing the work in that scenario.

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Parrek t1_j8j1x62 wrote

Usually the battery or another power source maintaining the magnetic field. Otherwise, the back current induced by the object being picked up would cancel everything out

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DamionFury t1_j8j6cgr wrote

Ah yes. That's right. I also remember we talked about the case of permanent magnets and objects suspended above them. I don't remember what his answer was and I wouldn't be surprised if he told me to try to work it out for myself because my questions were holding the class up.

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kkngs t1_j8l4jhj wrote

If the object is just being suspended by the permanent magnet, being held still against the force of gravity, then no work is being done. It’s not conceptually different than being held up by a shelf.

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