- Objects that rotate experience torque.
- Objects that rotate turn around some fixed point.
- When measuring torque, the point of rotation is called the pivot point.
- Torque is the product of force times force’s distance is from the pivot point.
Everyday Examples of Torque
1. Opening the lid on a jar is caused by torque, and the center of the lid is the pivot point. The distance is measured from the pivot to the edge of the lid where the force is applied.
2. A merry-go-round rotates about a center point. Thus, force applied to the merry-go-round causes it to turn about its axis, center point.
In summary, torque is a turning force. Torque can be measured using this equation:
Torque= force x distance
Teaching Tips from Janice
During my teaching career, I taught math and science for one year on an army base in Germany. My classroom was in a metal quonset hut behind the main school building. Wind blew through the crack around the windows causing the curtains to flutter. I just wore more clothes to stay warm. But the great thing about this building was it had lots of room and I was the only teacher using it. YEA!
There was a lot of construction work being done around the school by local Germans. I spoke no German and few of the workers spoke English, but I managed to get a a saw-horse and board transported to my classroom. With the board placed across the saw-horse the materials were transformed into a a see-saw. My students were so excited.
I used the see-saw to teach basic algebra. I asked two boys to sit on the board and move back and forth from the center until they could balance on the board. This meant that they could hold their legs up and the board would remain relatively horizontal for a few seconds. The distance each boy was sitting from the pivot point of the see-saw was measured. Next, a bathroom scale was used to measure the force weight of ONLY one of the boys.
Use this formula F1 x d1 = F2 x d2 to calculate the weight of the second boy.
It doesn’t matter what units are used to measure the force weight or distance. A bathroom scale was used and weight was measured in pounds, thus the unknown weight was in pounds. The distance unit was centimeters.
F1= weight of Juan= ?
d1= distance of Juan from the pivot= 100 cm
F2= weight of Tyler= 90 lbs
d2= distance of Tyler from the pivot= 120 cm
F1 x d1 = F2 x d2
F1 =F2 x d2/d1
Answer: Juan weighs 108 lbs.
Check the accuracy of your calculations. Have Juan use the bathroom scales to measure his weight. Were the calculations correct??? If not, give reasons for the error.
The diagram shows a balanced see-saw.
This is because the torque on each end of the board is equal.
Teaching the Fun of Math provides teaching tips for introducing algebra problems. Student worksheets are provided.