Rocket tries to lift a bucket of blocks with one hand. "Too heavy!"
Raven hangs a rope over a chair and ties on another bucket.
"What do you notice now?" she asks.
Nova glows on the ropes. "Would you like a hint? Which side is heavier?"
The elevator ropes hang over the sheave at the top.
The car hangs on one end.
The counterweight hangs on the other end.
A rope over a wheel is called a pulley. Builder's Lab builds pulleys.
This week, we look at the car and the counterweight.
The counterweight is heavy, about as heavy as the car.
The two sides almost balance.
So the motor does not lift the whole car alone.
It only needs to tip the balance.
That means the motor needs less power.
An electric motor turns the sheave.
The ropes grip the grooves in the sheave.
When the sheave turns, the car moves.
A machine brake holds the car still at each floor.
| Side | When the car goes up | When the car goes down |
|---|---|---|
| Car | Rises | Sinks |
| Counterweight | Sinks | Rises |
| Sentence | True or false? |
|---|---|
| The counterweight is about as heavy as the car. | ? |
| The motor lifts the whole car by itself. | ? |
| A motor turns the sheave. | ? |
| A brake holds the car still at a floor. | ? |
You found out why a counterweight helps. Wow!
Tomorrow, we build a cardboard elevator.