Equilibrium

What is a pivot?

What is a pivot?

A point where an object can rotate around

Define a moment, the equation for it and its unit

Product of the force and the perpendicular distance from the force to the pivot OR the rotational force about a pivot

M = Fd

M = moment, Nm, kgm²s^-2

F = force, N, kgms^-2

d = perpendicular distance from pivot, m

What happens when the force is parallel to the pivot?

A moment is not produced

State the principle of moments

‘For a body in equilibrium , the sum of the clockwise moments about ANY point is the sum of the anti clockwise moments about the SAME point’

What is a torque, its equation and its unit

Product of one of the couple forces and the perpendicular distance between the couple OR the rotational effect of a couple

T = Fd

T = torque, Nm, kgm²s^-2

F = force of one of the couples, kgms^-2

d = perpendicular distance between the couple, m

What are torques produced by?

Couples

What are couples?

A pair of equal and opposite PARALLEL forces separated by a perpendicular distance that causes rotation

They create no resultant force and instead create a rotational force called a torque

What is the method behind solving moment questions?

1) Resolve all forces acting on the object into vertical and horizontal components.

2) The resultant force in each direction MUST be 0 IF its in equilibrium.

3) Determine the total clockwise and anti-clockwise moments in each direction.

4) Use letters to represent unknown forces/distances, then use Pythagoras/sine/cosine rules to determine the unknown values.

Define the centre of mass

The point where the mass of an object is concentratedD

Define the centre of gravity

The point where the weight of an object acts