What is a Homopolar Motor and how do they work?

Homopolar has nothing to do with gay people living in Lapland. This term basically means that the direction of the magnetic field does not change. These are the simplest type of motor and was first made by Faraday himself in 1821. They use direct current and convert it into rotational energy. They are so easy that I even made one, just click here to see my Instagram postOne can make a homopolar motor with just a battery, some wire and some magnets.

dnp homopolar motor set up.PNG
YouTube screenshow of the homopolar motor set up

DNP made one of these motors in their YouTube video that you can find here

As you can see from the image the homopolar motor is set up as follows. Magnets go on the end of the battery. The wire must be balanced in a way to cause low friction but still make contact with the magnets.

But when he let goes it spins? WHY!?

To understand why this motor works it requires some fairly basic electromagnetic understanding. First lets understand where the current is flowing. The wire allows current to flow from the positive end of the battery, through the wire, into the magnet and into the negative end of the battery. When the current is flowing horizontally through the magnet it is passing through a magnetic field. And the Lorentz force will act perpendicular to both the field (acting up into the battery) and the current (acting horizontal to the ground) the force is therefore at a tangent to the magnet surface. As the wire rotates the force remains at a tangent as the magnet curves. The constant force can accelerate these to high speeds – the reason why mine kept falling off sadly

Interesting bits

If you want to know if a battery is dead, you can just drop it on a surface bottom first. If it bounces it has no charge. If it sticks the landing (without bouncing) then it is likely to be charged. These motors will drain batteries quickly as high current can flow through the wire, be careful because this means the wire can get hot. Neodymium magnets are very strong so be careful with them too. I believe these are the type of magnets DNP used in his video. Neodymium magnets only a few mm diameter can have pulling forces of several kilograms, sometimes strong enough to remove fingers! Go to two minutes in this video 

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