I recently received a question from Jack, an eight year-old. I must admit that I was surprised at the question. But, after thinking about it, it is something that even very young learners are familiar with yet rarely given information about.  Jack’s question was: “I want to know more about tork motion.”

Jack was curious about TORQUE, which is a turning force that causes something to turn in a circular motion. When you turn a doorknob–you are applying torque on the knob–it turns in a circle. When you open the lid on a jar, you apply torque causing the lid to turn in a circle.

Sometimes you apply torque, but the object doesn’t turn in a complete circle. For example, when you sit on a see-saw, your weight produces torque and the see-saw moves down. The board of a see-saws rotates around a support.

The point about which an object can rotate if supported there is called the fulcrum. This makes the center of the board of a see-saw its fulcrum. A see-saw can be balanced when the torque (turning force) on one side of the fulcrum equals the torque on the other side. The torque on each side is determined by multiplying the weight of the person times his or her distance from the fulcrum.The equation for this relationship is:

weight x distance = weight x distance

Since torque = weight x distance, if the two people do not weigh the same, the heavier person has to sit closer to the fulcrum, so that the products of their weight x their distance from fulcrum is equal.

You can confirm this on a see-saw as well as performing an experiment using a suspended ruler as the see-saw and spring clothespins as weights. The ruler will balance if the weights are attached at equal distances from the fulcrum. See TORQUE: SEE-SAW for instructions and more information about torque.

For more infomation and activities about torque, see Janice VanCleave’s book:

204 Sticky, Gloppy, Wacky & Wonderful Experiments

Photo by protoflux