How do electric motors make things move?

1. Flip a switch and the fan whirls and the toy car rolls away. Inside each one is a small electric motor that turns electricity into movement.
2. Every magnet has a north pole and a south pole. Opposite poles pull together, and matching poles push apart. Motors use these pushes and pulls.
3. When electricity flows through a coil of wire, the coil becomes a magnet: an electromagnet. Switch it off, and the magnet goes away.
4. Put the coil between two magnets. One side of the coil is pushed up and the other side is pushed down, so the coil twists around its middle.
5. After half a turn, the pushes would stop the coil. So a split ring called a commutator flips the current each half turn, and the coil keeps spinning the same way.
6. Motors are all around you: in fans, toy cars, washing machines, drills and conveyor belts that carry boxes in factories.

This model motor has no cover, so you can see every part. Tap each one to watch it work.

• Magnets. A north pole on top and a south pole below make a strong magnetic field across the coil. The magnets never move.
• Coil. The coil is many turns of thin copper wire. When current flows, the magnets push one side up and the other side down, so the coil turns.
• Shaft. The coil is fixed to the shaft, a strong metal rod. When the coil turns, the shaft turns, and it can drive a fan, a wheel or a belt.
• Commutator. The commutator is a copper ring split into two halves. It turns with the coil and flips the direction of the current every half turn.
• Brushes. The brushes are blocks of carbon pressed against the spinning commutator by springs. They let electricity flow into a part that is turning.
• Battery. The battery pushes current through the wires, brushes and coil. Turn it around and the current flows the other way, so the motor spins backward.
• Bearings. The bearings hold the shaft in place and let it spin smoothly with very little rubbing.
• Fan. The fan is the load: the job the motor does. The faster the shaft turns, the more air the fan pushes.

Turn up the battery, change the magnets and choose a job for the motor. Then try flipping the battery. What happens?

Experiment: What will happen if you flip the battery around while the motor is running?

1. Turn the battery up until the motor spins.
2. Notice which way the coil and fan turn.
3. Switch on Flip the battery and watch again.

What we found: Flipping the battery makes the current flow the other way through the coil. Then the magnets push each side the opposite way, so the motor spins backward. That is how toy cars drive in reverse!

Turn on JavaScript to try it yourself.

Build a motor that carries all 3 parcels up the belt into the truck before it leaves.

Magnets have two ends, called poles: north and south. A north pole and a south pole pull toward each other, while two north poles (or two south poles) push each other away. The space around a magnet where you can feel these pushes and pulls is called its magnetic field.

Electricity can make magnets too. When current flows through a coil of wire, the coil becomes an electromagnet with its own north and south poles. Switch the current off and the magnetism disappears. The more turns of wire, the stronger the electromagnet.

In a motor, the coil sits between two magnets. The magnets push one side of the coil up and the other side down, so the coil twists. After half a turn, the pushes would hold the coil still. That's why motors have a commutator: a split ring that flips the current every half turn so the coil keeps spinning the same way.

To make a motor spin faster, you can use a bigger battery voltage. To make it stronger, you can use stronger magnets or more turns of wire. Flip the battery around, and the motor spins backward. Toy cars use this trick to drive in reverse.

Key words

Magnetic field

The space around a magnet where it pushes or pulls.

Electromagnet

A coil of wire that becomes a magnet when current flows through it.

Commutator

A split ring that flips the current every half turn so the motor keeps spinning one way.

Torque

A turning push.

Back EMF

The voltage a spinning motor makes, which pushes back against the battery and limits the current.

Stall

When a motor's load is too heavy and it can't turn.

Check your thinking

1. What turns a coil of wire into a magnet?

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   Electricity flowing through it. Current flowing through a coil makes a magnetic field, so the coil becomes an electromagnet.

2. What do two north poles do when you bring them together?

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   They push each other away. Like poles repel and unlike poles attract.

3. What would happen to a motor with no commutator?

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   The coil would rock back and forth and stop. Without the flip, the pushes hold the coil upright after half a turn, so it stops.

4. How can you make a motor spin the other way?

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   Turn the battery around. Reversed current means reversed pushes, so the coil turns the opposite way.

5. Why does a motor draw the most current when it is stalled?

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   With no spinning there is no back EMF, so I = V ÷ R. Back EMF grows with speed. At zero speed it is zero, so only the coil's resistance limits the current.

6. Which change makes a motor spin faster?

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   Using a bigger battery voltage. More voltage pushes more current, which makes a stronger turning push.