Turning Effects Of Forces

By: Rasha KhateebTurning Effects Of Forces

The Moment Of A ForceMoment: The Quantity that tells us the turning effect of a force about a pivot The moment of force is bigger if :The force is biggerIt acts further from the pivotIt acts at 90 degrees to the object it acts on

BeamBeam: A long, rigid object that is pivoted at a point. If the beam is to be balanced the moments of the two forces must cancel each other out.

EquilibriumEquilibrium is when a beam is balanced. If an object is Equilibrium:1- the forces on it must be balanced 2- the turning effects of the forces on it must also be balanced

Calculating momentsMoment of a force = force x perpendicular distance from pivot to forceM = F * D

The unit of moment of force= Nm (Newton Metre)

Balancing moments

Total clockwise moment = total anticlockwise moment

Worked ExampleQuestion: Identify the Clockwise and anticlockwise forces. Two forces act clockwise: 20 N at a distance of 0.5 m, and 10 N at 1.5 m, one force acts anti clockwise: the force F at 0.5 m from pivot.

F 20N 10NAnswer: Clockwise moments = anticlockwise moments (in magnitude) (20N x 0.5M) + (10N x 1.5m) = F x 0.5 m 10Nm + 15Nm = F x 0.5 m 25 Nm= F x 0.5 m F= 25Nm/0.5m= 50 N

Centre Of massCentre of mass: The point at which the mass of an object can be considered to be concentrated.

How to locate the centre of mass

SummaryThe moment of a force is a measure of its turning effectWhen a system is in equilibrium, the resultant force is zero and the resultant turning effect is zero. For an object to be stable, its centre of mass must be low down and it must have a large baseMoment of a force = force x perpendicular distance from pivot to force

Questions

Question 1 What quantity is a measure of the turning effect of a force?

Question 2What two conditions must be met if an object is to be in equilibrium?

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