Everything Science Grade 11

CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.6

as the product of the distance from the support or pivot (r) and the component offorce perpendicular
to the object, F⊥.

τ = F⊥· r (12.9)

Torque can be seen asa rotational force. Theunit of torque is N·m and torque is a vector quantity.
Some examples of where torque arises are shown in Figures 12.13, 12.14 and 12.15.

F

r

τ

Figure 12.13: The forceexerted on one side of asee-saw causes it to swing.

F

r

τ

Figure 12.14: The forceexerted on the edge of apropeller causes the propeller to spin.

Tip

Loosening a bolt: if you

are trying to loosen (or

tighten) a bolt, apply the

force on the spanner fur-

ther away from the bolt,

as this results in a greater

torque to the bolt mak-

ing it easier to loosen.

F

r

τ

Figure 12.15: The forceexerted on a spanner helps to loosen the bolt.

For example in Figure 12.15, if a force F of 10 N is applied perpendicularly to the spanner at a distance
r of 0,3 m from the centre of the bolt, then the torque applied to the boltis:

τ = F⊥· r

= (10 N)(0,3m)

= 3N· m

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

τ = F⊥· r

= (10 N)(0,15m)

= 1,5N· m

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

Tip

Any component of a

force exerted parallel

to an object will not

cause the object to turn.

Only perpendicular

components cause

turning.