YouTube: https://youtube.com/watch?v=utJq81nB-3s
Previous: Introducing: SciShow Talk Show! Emily, Rhinos, and Cas the Arctic Fox
Next: 3 Weird Ways Olde Tyme People Got High

Categories

Statistics

View count:383,189
Likes:6,527
Dislikes:92
Comments:1,068
Duration:03:42
Uploaded:2013-01-29
Last sync:2018-04-25 18:20
Hello, this is Hank Green, and welcome to another SciShow  experiment.  I have in my hand a small disk magnet, a D battery, a piece of copper wire, and a drywall screw.  With those four objects I'm gonna build an electric motor just powerful enough to make this screw spin, but also, strong enough to blow your mind.

(Intro music plays)

Start with a magnet, I'm using a neodymium magnet because it's round and thin and very powerful, and plated to conduct electricity. Attach it to the flat end of the screw. Then with the magnet attached to the screw, turn the battery upside down and touch the screw to the little node thing on the bottom. It should just hang there. Then hold the copper wire to the other end of the battery, and ever so carefully, touch the magnet with the other end, and magic. If you can hold it in place for twenty seconds, the screw will be moving at ten thousand revolutions per minute.

It's the world's simplest electromagnetic motor, known as a homopolar motor, because it works without having to reverse its current, like most other electric motors. It may not be pretty, it's definitely not efficient, and it doesn't have many practical applications, but this little contraption does demonstrate the concepts that make every motor work.

An electric motor simply converts electrical energy into mechanical energy. In this case, we're using the energy in the battery to create rotational motion. Like all motors, this simple motor uses magnetic fields to create the motion with the help of something called the "Lorentz Force".

You gotta remember here that electricity and magnetism are the same force: electromagnetism -- that we just happen to notice and describe in two different forms. When the current flows out of the battery, it creates a magnetic field around it; by the same token, this magnet was permanently magnetized using a ridiculous amount of electrical energy. You can't have electricity without magnetism. They're the same thing. So when you combine an electric current from a battery with a magnet, you're basically creating two overlapping magnetic fields, and when these fields interact, they create the Lorentz Force.

As Dutch physicist Hendrik Lorentz calculated in the mid 1800s, this force is exhorted on the charged particles that carry the electric current at a precise right angle to the direction in which they're flowing. In other words, the Lorentz Force is applied perpendicular to the current. So when you connect the copper wire from one end of the battery to the other end of your motor, you're completing an electric circuit. You're allowing the flow of particles from one of the battery's electrodes to the other. In this case, the current is flowing from the positive electrode, or the top of the battery, even though it's upside down, down the screw, out the side of the magnet, and then back through the wire to the bottom.

Basically, the current is running down the motor's axis of symmetry, but because the current is flowing through an additional magnetic field given off by the magnet, the Lorentz Force pushes those particles at a ninety degree angle, forcing them to move perpendicular to the axis of symmetry. This force on the charged particles inside the screw is what makes it spin.

All electrical motors work on this same principle. But even though this motor is a good way to see deliverance force in action, you won't find many applications for it. That's because it's producing a continuance flow of current which will drain this big old battery pretty fast, and also get it pretty hot. Most battery powered electric motors like you'll find in toys and other gadgets use a series of coils to create and amplify the magnetic field instead of a permanent magnet to make it more efficient.

So, not very efficient, but very simple, and also pretty cool. If you have any other ideas for experiments we can do here on Scishow, you can leave them in the comments below -- we'd love to have your suggestions. If you have any questions or comments, we're on Facebook and Twitter and of course, down in the comments below. And if you wanna keep getting smarter with us here on Scishow, you can go to YouTube.com/Scishow and subscribe.