PHY3: MOMENTS

MOMENTS

A moment is concerned with the turning effort of a force

When two or more forces act at a point, they tend to make that body rotate e.g opening a door, turning a tap, turning a nut using a spanner, turning the steering wheel of a car etc.

The point about which the body turns is called the fulcrum or pivot.

A very large turning effort can be achieved with comparatively small force provided the distance from the fulcrum is large.

Magnitude of this turning effort is called a moment of force.

Moment of force is the product of force and its perpendicular distance of its line of action from the turning point [pivot].

Moment of force = force x perpendicular distance from pivot.

The S.I unit of moment is the newton metre (Nm).

Moment has both magnitude and direction hence is a vector quantity.

A moment of force may have a turning effect in clock wise or anti clockwise direction. 

PRINCIPLE OF MOMENTS OF FORCE.

When a body is in equilibrium, the sum of the anticlockwise  moments about any point is equal to the sum of the clockwise moment about the same point.

E.g. A young boy of mass 25kg is playing with his sister of mass 40kg on a wooden plunk of length 5m pivoted at exactly the centre. If the boy sites 2m from the pivot, how for a way from the pivot should the sister be in order for the plunk to balance horizontally. Anti clockwise moment = F x d = 250 x 2                                               = 500N

Clockwise moment = 400 x X = 400X ,         At balance,400x=500.

X = 1.25m .

THIS VIDEO IS ABOUT MOMENTS AND HOW THEY WORK