5 ms·
A ball dropped near the earth's surface will always fall towards the centre of the earth at ~9.81m/s^2 no matter what it has done previously. A chunk of iron p
by womble2 24d ago
A ball dropped near the earth's surface will always fall towards the centre of the earth at ~9.81m/s^2 no matter what it has done previously.
A chunk of iron put into a 1μT magnetic field will behave differently depending on what other magnetic fields it has been in recently.
- thaumasiotes 24d ago> A ball dropped near the earth's surface will always fall towards the centre of the earth How exactly does this address "whether it was recently thrown upward or dropped from above"? A ball in a given location will do something unpredictable if you have no information about its past. Is that hysteresis?
- nkrisc 24d agoYou don’t need information about its past. Everything you need to know to predict its future state is contained in its current position and velocity at the moment you measure it.
- yummybrainz 24d agoIs there no measurable quantity in the current state of a magnetized ball that would predict its behavior in a magnetic field then? I'd be surprised if that were the case: seems like it'd violate some sort of "locality", where the future should depend entirely on the present state. Is it just that there's unidentified present state that's perhaps more easily characterized by knowing the history? Or is it somehow unidentifiable in principle?
- PowerElectronix 24d agoYeah, the current magnetization of the sphere carries all the history of the magnetic fields it's been in in its value. The hysteresis in the material only means that if you apply 1T to it to magnetise (supposing the ball starts with zero magnetisation) it and then apply 0T to demagnetise it, the remanent field in the ball would be like 0.4T due to hystetesis, you need to apply something like -0.4T to leave it as it started.
- yummybrainz 12d agoThank you! That makes sense to me.
- ErroneousBosh 24d agoIf it was recently thrown upward, it is either still travelling upwards away from the centre of the Earth, or it is falling downwards towards the centre of the Earth. So its past is kind of irrelevant. At some point if nothing is supporting it, it will fall towards the centre of the Earth. This is just high school physics.