Torque and Levers, Grade 11 physics
Torque

When an object is fixed or supported at one point and a force acts on it a distance away from the support, it tends to make the object turn. The moment of force or torque (symbol, τ read tau) is defined as the product of the distance from the support or pivot (r) and the component of force perpendicular to the object, F$_{⊥}$.

τ = F$_{⊥}$ · r (12.9)​

Torque can be seen as a rotational force. The unit of torque is N·m and torque is a vector quantity. Some examples of where torque arises are shown in Figures 12.17, 12.18 and 12.19.

For example in Figure 12.19, if a force F of 10 N is applied perpendicularly to the spanner at a distance r of 0,3 m from the center of the bolt, then the torque applied to the bolt is:

τ = F$_{⊥}$ · r = (10 N)(0,3 m) = 3 N · m​

If the force of 10 N is now applied at a distance of 0,15 m from the centre of the bolt, then the
torque is:

τ = F$_{⊥}$ · r = (10 N)(0,15 m) = 1,5 N · m​

This shows that there is less torque when the force is applied closer to the bolt than further away.

Important: Loosening a bolt
If you are trying to loosen (or tighten) a bolt, apply the force on the spanner further away from the bolt, as this results in a greater torque to the bolt making it easier to loosen.
Important: Any component of a force exerted parallel to an object will not cause the object to turn. Only perpendicular components cause turning.
Important: Torques
The direction of a torque is either clockwise or anticlockwise. When torques are added, choose one direction as positive and the opposite direction as negative. If equal clockwise and anticlockwise torques are applied to an object, they will cancel out and there will be no net turning effect.

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Physics 11.II Force, Momentum, Impulse

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