Spin a Motor, Make Electricity?! The Surprising Link Between Motors and Generators

I’m Ken Kuwako, your Science Trainer. For me, every day is an experiment.

What Happens When You Spin a Motor With No Battery?

Hook a battery up to a motor, and it spins.

“Well, duh,” you might be thinking. But what if you skip the battery and spin the motor’s shaft by hand instead? What do you think would happen? It turns out this is where one of the great secrets of electricity is hiding.

It’s super easy: just pinch the motor’s shaft and spin it. Fingers alone aren’t great for getting up to speed, though, so I pressed a stick against the shaft and rolled it back and forth. Rubbing it with the stick makes it spin much faster than fingers can.

Then I connected the motor to an ammeter and spun the shaft. Whoa, current flowed! There’s no battery anywhere, and yet electricity is being made. Check out the video here.

Next, I connected this motor to a second motor and spun the first one’s shaft. The shaft of the second motor started turning all by itself!

The motor I spun made electricity, which traveled through the wires and powered the other motor. It’s like a relay race, with electricity as the baton.

Motors and Generators Are Two Sides of the Same Coin

That’s right: a motor and a generator are really one and the same, like the front and back of a coin.

Inside a motor, you’ll find magnets and a coil (a wire wound around and around). When current flows through the coil, the magnets push on it and make it spin. That’s how a motor works. Flip that around, and spinning the coil near a magnet produces current in the coil. This phenomenon is called electromagnetic induction, and it’s how a generator works. The very same parts can turn electricity into motion, or motion into electricity.

A familiar example: a hand-crank generator has a motor inside it. Turn the handle while it’s connected to a small bulb, and the bulb lights up, because the motor is working as a generator.

But here’s the twist. Connect a battery to the terminals of that hand-crank generator, and the handle starts moving on its own, without anyone touching it. The thing you were using as a generator suddenly becomes a motor!

“Motors as Generators” Are All Around Us

This trick is hard at work in our everyday lives. Electric and hybrid cars, for example, use their motors as generators when you hit the brakes, turning that braking energy into electricity and storing it in the battery. Trains do something similar with a system called regenerative braking, which generates electricity and saves it as the train slows down. The motor that powered you forward transforms into a generator when it’s time to stop.

The generators in power plants work on the same basic principle, too. Water or steam power spins a huge shaft, and that spinning creates electricity. The tiny motor I spun with a stick and my fingers and the giant generators in power plants are, believe it or not, close relatives.

I hope you’ll try this yourself with a toy motor! Spinning a motor you’ve always powered with electricity and making electricity with your own hands is an experience you won’t soon forget.

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Making the wonder and fun of science feel closer to home! This site collects fun science experiments you can do at home, along with tips to make them work. Try searching around!
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