Let's talk about torque
02/10/2010 | WAYFARER | TECH
I remember vividly how, one day some years ago, I parked in the Epping industrial area near a tyre fitment shop. Sitting in my car, I noticed a large yellow tractor with massive tyres pull up and park in front of the tyre shop. A workman came out of the shop and spoke to the driver. The workman went back into the shop and soon returned with a large wheel spanner and attempted to loosen the nuts of the wheel. But, try as he might, the nuts refused to budge.
And this is where I was treated with a visual demonstration of how torque works. The workman went into the shop again and returned with a very long hollow metal pole and fitted it over the handle of the spanner. He then gave a firm single-handed tug on the far end of the pole, and immediately the nut came loose. Amazing!
So what ghostly, eerie forces are at work here? Well, it is really very simple. To loosen or tighten a turning mechanism, when requires torque. Torque has two components, i.e. force and distance (distance from the point of turning, called the fulcrum or pivot). So even though the workman initially used all very much strength, his hand was not that far from the fulcrum (the wheel nut, in this case) because of the short handle. When the pole was added over the handle, the distance between the fulcrum and the workman's hand increased, increasing the net torque.
Mathematically, we right:
Torque = Force X Distance
Example: Consider the diagram below
1. What is the magnitude of the torque that is exerted from point A?
2. What is the magnitude of the torque that is exerted from point B?
3. What is the net torque in the above system?
Solution
Let clockwise be positive (always write this down)
1. TorqueA = ForceA X DistanceA = 25 X 2 = 50 N•m clockwise
2. TorqueB = ForceB X DistanceB = 30 X 1,5 = 45 N•m anti-clockwise
3.
TorqueNET = TorqueA + TorqueB = 50 + (-45) = +5 N•m
But positive means clockwise and negative means anti-clockwise, therefore +5 N•m means
5 N•m clockwise.