Turning effect
A force may cause an object to turn about a pivot.
The turning effect of a force is called the moment of the force.
Moments act about a pivot in a clockwise or anticlockwise direction.
Calculating the moment of a force
The size of the The moment of a force is the turning effect of the force. Moment = force x perpendicular distance from the pivot. can be calculated using the equation:
moment of a force = force F x perpendicular distance from the pivot d
moment = F x d
- force F is measured in Unit of force named after British scientist Isaac Newton (1642-1727). Eg, the frictional force on the boat is 20,000 N.
- distance d is measured in metres (m)
- moment is measured in newton metres (Nm)
The distance from the pivot which makes a right angle with the line of action of the force. from pivot to force d = 0.50 m.
Force F = 10 N
Moment = Fd
Moment = 10 N x 0.50 m
Moment = 5 Nm
This is a clockwise moment.
The force will rotate the object in a clockwise direction about the pivot.
Question
A force of 15 N is applied to a door handle, 12 cm from the hinge.
Calculate the moment of the force.
Perpendicular distance from pivot to force d = 12 cm = 0.12 m.
Turning force F = 15 N.
Moment = Fd.
Moment = 15 N x 0.12 m.
Moment = 1.8 Nm.
The moment of the force is 1.8 Nm.
Question
Question
A force of 40 N is applied to a spanner to turn a nut.
The perpendicular distance is 30 cm.
Calculate the moment of the force.
Perpendicular distance from pivot to force d = 30 cm = 0.30 m.
Turning force F = 40 N.
Moment = Fd.
Moment = 40 N x 0.30 m.
Moment = 12 Nm.
The moment is 12 Nm. This is a clockwise moment.