Video: Calculating the Torque Produced by a Force

A washing line is attached to the top of a pole, as shown in the diagram. What is the magnitude of the torque at the top of the pole produced by the tension in the washing line?

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Video Transcript

A washing line is attached to the top of a pole as shown in the diagram. What is the magnitude of the torque at the top of the pole produced by the tension in the washing line?

Okay, so in this question, we’ve got a pole firstly and we’ve got a washing line. The washing line is attached to the top of the pole as we can see in the diagram. And we’ve been given the tension in the washing line, which happens to be 12 newtons, and the height of the pole, which is 1.5 meters.

What we’ve been asked to do is to work out the magnitude of the torque at the top of the pole produced by the tension in the washing line. Now the washing line is going to be pulling in this direction on the pole. And because the pole is attached to the ground, this is where the pivot point is going to be.

In other words, the connection between the pole and the ground is the fulcrum. And so the tension of the washing line is working to pull the pole in this direction. In other words, it wants to take the poll which is currently vertical and rotate it clockwise. And this rotation is about the fulcrum which is the connection between the pole and the ground.

So in order to work out the torque, which we can recall is given by multiplying the force applied by the perpendicular distance between the fulcrum and where the force is applied, we need to say that the torque is equal to the tension in the string, which is the force applied — and that is 12 newtons — multiplied by the distance between the fulcrum, which is here, and the point at which the force is applied, which is here.

And that distance is 1.5 meters. And so once we evaluate the right-hand side of the equation, we find that the torque produced at the top of the pole by the tension in the washing line is 18 newton-metres. And that’s the answer to our question.

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