Professor Eric Laithwaite: Magnetic River 1975
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a demonstration of electromagnetic induction effects, such as a conducting cylinder spinning next to a ring around a solenoid.
Recommended by 0 people across 0 different months, 2019 to 2021.
What it is
An 18-minute 1975 presentation by Professor Eric Laithwaite of Imperial College London, demonstrating magnetism and the linear motor with live experiments. It is part of the Imperial College video archive.
What people said
Cites spheroidic · 2019-09 · Physics Stack Exchange · on “Why does a conducting cylinder spin when held next to a conducting ring around a solenoid?”
My uncle showed me this video [this video] . I understand that the magnetic field from the solenoid induces a current perpendicular to it in the ring. However, I don't see why this current would result in a torque about the longitudinal axis of the brass cylinder. My guess is that the magnetic field from the ring is less uniform than that of the solenoid, which somehow results in a torque in the cylinder. Can anyone explain how this actually happens?
Cites Deschele Schilder · 2020-07 · Physics Stack Exchange · on “Can a permanent magnet attract things permanently? If yes, then doesn't it violate law of conservation of energy?”
Let me start by saying it's a very difficult mathematical job to calculate the force between macroscopic magnets. See this [LINK] Wikipedia article. But I'll try to explain in words why conservation of energy isn't violated as you ask in the question body. Say we start with one magnet. Now say we put a lot of magnets (or substances that react to it by getting magnetized by the magnet, say an iron nail) around it. All the magnets will experience a torque and their north poles will be aligned with the magnets south pole and vice-versa and will start to move to one of the two poles (depending on their position to the magnet). The non-magnetic substances which can be magnetized by the magnet dev
Cites oliver · 2021-07 · Physics Stack Exchange · on “A Material Who's Magnetic Polarity is Defined by an Outside Magnet”
The fact that materials adjust their magnetic polarity to an external field ("outside magnet") is the norm rather than an exception. There are several possibilities for what you specifically desire: Using material diamagnets is out of the game, because diamagnetism is extremely weak ( bismuth [LINK] is a stronger diamagnet, but still pretty weak) Using ferromagnets might naively seem feasible, because ferromagnetism is pretty strong for some materials (iron, cobalt, rare-earth compounds), but then again, although the induced north poles next to "S" would mutually repel each other, they would both be attracted much more strongly by "S", resulting in a net attraction effect Using paramagnets..