How do elevators work?

1. You press the call button. A computer called the controller gets the message and sends the elevator car to your floor.
2. Behind the walls is a tall shaft. The car hangs from several steel ropes that go up to a big wheel at the top.
3. The other ends of the ropes hold a heavy counterweight. When the car goes up, the counterweight goes down, like two kids on a seesaw.
4. An electric motor turns the wheel. Its grooves grip the ropes, so as the wheel turns, the ropes move and the car rises. The counterweight helps with the lifting.
5. Elevators have lots of safety parts. If the car ever moved too fast, a speed checker would set off brakes that grip the rails. Springs at the bottom are a soft cushion.
6. Sensors tell the controller where the car is, so it slows down and stops level with the floor. The doors open, and in you go!

This building is see-through! Tap each part of the elevator to watch it work.

• Motor. An electric motor at the top turns the drive wheel. A brake holds the wheel still whenever the car stops.
• Drive wheel (sheave). The ropes sit in grooves around this wheel. When it turns, it pulls the ropes along by friction.
• Steel ropes. Several steel ropes, each made of many twisted wires, hold the car. Together they are many times stronger than they need to be.
• Elevator car. The car is the little room you ride in. It has buttons, lights and a sensor that weighs the load.
• Counterweight. A stack of heavy metal blocks on the other end of the ropes. It balances the car, so the motor works less.
• Guide rails. Steel rails run up the shaft. Rollers on the car and counterweight follow them, so nothing swings.
• Speed governor. A loop of rope turns this wheel as the car moves. If the car went too fast, it would set off the safety brakes.
• Buffers. Springs or oil-filled pistons in the pit would cushion the car or counterweight if it ever went too low.
• Doors. The car doors and the floor doors open together. Locks keep floor doors shut unless the car is right there.
• Buttons and controller. Buttons send calls to the controller, a computer that decides where the car goes next.

Add riders, send the car to different floors and watch how hard the motor works. Then take the counterweight off. What changes?

Experiment: What happens to the motor's job if you take the counterweight away?

1. Add a few riders and send the car to the top floor.
2. Watch the motor effort meter and the balance.
3. Turn off the counterweight and send the car again.

What we found: With the counterweight, the car and the weight nearly balance, so the motor only lifts the small difference. Without it, the motor has to lift the whole car and everyone inside!

Turn on JavaScript to try it yourself.

Deliver all 7 riders to their floors. The car holds 4 people at a time. Tap floors to plan your stops.

Most tall buildings use traction elevators. The car hangs from steel ropes that loop over a grooved wheel at the top of the shaft. The other ends of the ropes hold a counterweight. An electric motor turns the wheel, and the grooves grip the ropes, so the car moves up or down.

The counterweight is the clever part. It weighs about as much as the car plus half a full load of people. Because the car and the counterweight balance each other like a seesaw, the motor only has to lift the difference. That saves a lot of energy.

Elevators are among the safest ways to travel. Several ropes share the load, and together they are many times stronger than they need to be. A speed governor checks how fast the car moves, and if it ever went too fast, safety brakes would grip the rails. Doors open only when the car is at the floor.

A computer called the controller decides where the car goes. Usually it keeps going in one direction while anyone needs to go that way, then turns around. Short buildings sometimes use hydraulic elevators instead, which push the car up with a piston.

Key words

Counterweight

A heavy weight on the other end of the ropes that balances the car.

Sheave

The grooved wheel that the motor turns to move the ropes.

Traction

The grip between the ropes and the grooved wheel.

Speed governor

A device that senses if the car goes too fast and sets off the safety brakes.

Rated load

The heaviest load an elevator is designed to carry, such as 630 kg or 8 people.

Check your thinking

1. What does the counterweight do?

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   Balances the car so the motor works less. The counterweight balances the car, so the motor only lifts the difference.

2. What lets the wheel move the ropes?

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   Friction in the grooves of the wheel. The grooves grip the ropes, so they move when the wheel turns.

3. What would stop a car that moves too fast?

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   A speed governor sets off brakes on the rails. The governor senses the speed and makes the safety brakes grip the rails.

4. With 315 kg of imbalance at 1.6 m/s, about how much power must the motor supply (ignoring losses)?

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   About 5 kW. P = F × v = 315 × 9.81 × 1.6 ≈ 4,900 W, which is about 5 kW.

5. Why do elevators usually finish going one way before turning around?

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   It saves time and energy for everyone. Stopping on the way and then turning around means fewer back-and-forth trips.