Moments

"What is the turning effect of a force called?

The moment of the force."

"What can a force, or a system of forces, cause an object to do?

Rotate (turn about a pivot)."

"What is the equation for the moment of a force, in words?

moment of a force = force × distance"

"What is the equation for the moment of a force, in symbols?

M = F d"

"In the moment equation M = Fd, what does the distance d mean exactly?

The perpendicular distance from the pivot to the line of action of the force. (It must be perpendicular – not just any distance to the force.)"

"What are the units in the moment equation M = Fd?

Moment M in newton-metres (Nm); force F in newtons (N); distance d in metres (m)."

"For a balanced object, how do the clockwise and anticlockwise moments compare?

The total clockwise moment about the pivot equals the total anticlockwise moment about that pivot. (This is the principle of moments.)"

"How do you find an unknown force or distance on a balanced object?

Set total clockwise moment = total anticlockwise moment, then rearrange to solve for the unknown. (Convert all distances to the same unit first.)"

"Name two devices that can transmit the rotational (turning) effect of forces.

A simple lever and a simple gear system."

"How does a lever transmit the rotational effect of a force?

It uses a pivot so that a force applied at a greater distance from the pivot gives a larger moment – acting as a force multiplier. (Longer distance from pivot = bigger turning effect for the same force.)"

"How does a gear system transmit the rotational effect of forces?

Gears pass the turning effect from one gear to another; a force on a gear with teeth further from the axle (larger gear) produces a larger moment. (Larger gear radius = bigger moment.)"