Torque
A torque is when we have a couple acting on an object, to rotate it.
It basically measures the magnitude of the turning effect (moment) caused by a couple.
Because it’s a rotation, it must have a moment!
Calculating torque
Section titled “Calculating torque”The turning effect is the sum of both moments in the couple.
- For example, if we have a couple with two forces:
- A
force away from the pivot, clockwise - A
force away from the pivot, clockwise
- A
- …then we know that the first moment must be
and the second moment must be . - Adding them together, we get
, so our torque is 25Nm.
We could also have done this by simply multiplying the force by the distance between the couple’s forces:
- That gives us the same torque of
.
Torque formula
Section titled “Torque formula”We can use that to write a formula for torque, which looks very familiar:
Where:
is the combined moment of the forces is the magnitude of a single force (one of the components of the couple) is the distance between the couple’s forces
Units of torque
Section titled “Units of torque”Torque is just the combined moment, so it’s measured in the same way: using newton-metres.
Calculations
Section titled “Calculations”Two forces of
Section titled “Two forces of act clockwise on a metal bar. The forces are away from each other. Find the turning effect.”The torque on a stick is 7Nm. The perpendicular distance between the couple is 3.5m. Find the sum of the magnitudes of the forces acting.
Section titled “The torque on a stick is 7Nm. The perpendicular distance between the couple is 3.5m. Find the sum of the magnitudes of the forces acting.”- The force of one is 2N
- So the combined force of both components of the couple must be
- Answer: