# Elevators and counter weight

In case of elevators we have motor attached to pulley, which has counter weight on one side and elevator car on the other side. Now let us say if elevator car is of 100 kg and counter weight is of 150 kg-then why don't elevator car just shoots up, what is preventing this to happen?

• You might as well ask, if the elevator car weighs more than the counterweight (e.g., because it is packed full of people), then why doesn't the counterweight just shoot up, and the elevator car fall to the bottom? Feb 25, 2021 at 16:57
• P.S.: 1000kg probably would be a more realistic number if we're talking about an elevator car that was designed to carry human passengers. Feb 25, 2021 at 17:00

The point of the counterweight is to reduce the overall force the motor has to apply to get the elevator moving and to stop it. The counterweight is designed to be approximately equal in weight to the elevator. So, when the elevator is stationary, the weights are balanced and the motor has to apply no force.

When the elevator is loaded with people, the effective weight the the motor has to move is only the difference between the elevator and counterweight. Whereas, if there were no counterweight, the motor would have to move the entire elevator plus the people, which would require a much greater force.