Torque
Torque is the turning effort.
To open a jar, you must apply a turning effort on the lid in a counterclockwise direction.
To close a jar, you must apply a turning effort on the lid in a clockwise direction.
The lid turns around a point in its center.
A merry-go round also turns around a center point. When a person gives the merry-go-round a push, they are applying an effort force (torque).
A see-saw turns around a center point. This point is in the center.
When a person on one side pushes against the ground so that her side of the see-saw moves upward, the opposite side of the see-saw moves 
downward.
For the see-saw to balance, the torque on one side must equal the torque on the opposite side. Even though the two on the see-saw have different weights, by changing their distance from the center point the turning effort can be the same on each side.
A see-saw can be used to teach algebra equations. In the image shown, assume the torque on each side is equal. Using the weight of the child on the right as 80 pound and at a distance of 36 inches from the center, calculate the weight of the child on the left if she is sitting 48 inches from the center. (Answer shown in the diagram)