Moments in Physics Flashcards

All 7 cards in this deck

What is the moment of a force?

The turning effect of a force about a pivot.

What is the equation linking moment of a force, force and distance, and what are the units of each quantity?

$M = F \times d$

Moment $M$ in newton-metres (N m), force $F$ in newtons (N), distance $d$ in metres (m).

True or false? In $M = F \times d$, $d$ is the distance from the pivot to the point where the force is applied, measured along the direction of the force.

False. $d$ is the perpendicular distance from the pivot to the line of action of the force.

What are the steps to calculate the moment of a force?

e.g. a force of $2.0$ N acts at a perpendicular distance of $7.5$ cm from the pivot

1. Convert the distance to metres: $7.5\ \text{cm} = 0.075\ \text{m}$
2. Substitute into $M = F \times d$: $M = 2.0 \times 0.075$
3. Give the answer in N m: $M = 0.15$ N m

Give two everyday examples in which a force causes an object to rotate.

Pushing a door handle to open a door; using a spanner to turn a nut.

(Also: turning a bicycle pedal, using a screwdriver.)

How can the moment about a pivot be increased without increasing the size of the force?

Apply the force further away from the pivot.

e.g. push on a spanner nearer its end.

True or false? If the perpendicular distance from the pivot is measured in centimetres, it must be converted to metres before calculating a moment in N m.

True. Moment in N m needs force in N and distance in m, e.g. $7.5$ cm $= 0.075$ m.