Rotational Motion - Self Test

Solution to Question 3: Net Torque

As with forces, individual torques can add to give the net torque.

In this question, we have three separate forces. All three forces act at a distance from the pivot point, O. This gives rise to three individual torques, each one caused by a separate force. Note that we have forces acting in different directions, and so may cause different directions of torque. Let's take the forces causing a counter-clockwise motion of the object to have positive torque. Clockwise motions will be taken to have negative torques.

Letting 1 be the torque caused by F1, similarly with 2 and 3, we can see that F1 and F2 both cause torques in the negative direction (ie. clockwise), while F3 causes a positive torque (ie. counter-clockwise). We need to consider this when summing the total torque,  on this object. 

Let's take each torque separately, beginning with the one caused by F1
The torque caused by F2,
And by F3,
Summing up 1,2, and 3, we get the total, or net torque.

Figure 1 Diagram from Question 3

Explanation of Torque
Continue to: Question 4: Angular Acceleration
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