Torque

Torque: Terms and definitions

• Torque can be thought of as a turning force or twist. • It has the symbol and units of Newton metres (Nm).For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt.

Where is the force applied and is the perpendicular distance from the pivot.

• Try closing a door, first from close to the hinges, then close to the handle… Discuss with a neighbour the differences between the two.

Close the Door

Pushing the door close to the handle is much easier. This is because although the torque needed to move the door is the same, the distance () from the pivot (hinges) is much larger.

With the same torque, pushing close to the pivot a much larger force is required.

When we apply the force the door turns on its hinges. Thus a turning effect (torque) is produced when we try to open the door. ..

Torque and Balancing

The concept of balancing torques is very familiar to us:

When Dad who has more mass (therefore greater weight force) wants to balance the see-saw with little Billy. He has to sit closer to the middle. This is because for the see-saw to balance, the Torques produced by their weights must be equal in magnitude.

Clockwise or Anti-clockwise?• On the previous slide the two torques produced had to be equal

in magnitude, but one was clockwise and one was anticlockwise. That’s right, torque is a vector too.

• When balancing torques the sum of the clockwise torques must equal the sum of the anticlockwise torques.

• To do this we usually take clockwise as positive and anti-clockwise as negative so that .

“Righty-tighty” and “lefty-loosey”.

• This is what we can use to distinguish between a clockwise or anti clockwise torque.

Picture the pivot as a bolt, the radius as a wrench and the force as the force your arm would produce.

The bolt would turn…ClockwiseThe torque produced is the same way the bolt would move: into the page.

The bolt would turn…Anti – ClockwiseThe torque produced is the same way the bolt would move: out of the page.