Force: Moments of a Force & Equilibrium

Moment of a Force Force multiplied by the perpendicular distance to the fulcrum M = Fd Vector quantity Unit = Newton metre (Nm) Fulcrum is a fixed point about which a rigid body is free to rotate The moment of a force can only be determined with reference to an axis

Lever A rigid body that is free to rotate about a fixed axis We most often deal with levers that pivot on a point, which is called the fulcrum Levers convert a small force applied over a long distance to a large force applied over a small distance Examples: Door handle Forearm pivots at the elbow

Couple A pair of equal and opposite forces whose lines of action do not coincide When a couple acts on a body, the resultant force is zero, but it has a turning effect Example: the forces exerted by one's hand on a screw-driver

Torque The torque of a couple is equal to the magnitude of one of the forces multiplied by the distance between them T = Fd Examples of torques are twisting a tap or the handle bars of a bicycle

Conditions for Equilibrium A body is in equilibrium when it is neither accelerating nor changing its rate of rotation Two conditions must be satisfied: The vector sum of the forces in any direction is zero The vector sums of moments about any points is zero (AKA the principle of moments)

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