A moment is the turning effect of a force: = force x perpendicular distance from pivot to line of action (f x s = Nm)
The principle of moments states that for an object in equilibrium... sum of clockwise moments = sum of anticlockwise moments
Centre of mass: is the point at which the weight of the body can be considered to act (It can also be described as the point at which the turning effect/moment/torque is equal to 0)
Torque: The tendancy of a force to rotate about a an axis.
Couple: Tries to turn something about an axis. Two forces equal in magnitude, acting in opposition directions, parrallel to one another, equidistant from the point of rotation. Mangnitude = one force x total distance between them (Nm) The moment of a couple, sometimes called the Torque
Support problems: clockwise = anticlockwise (X x D1 = Y x D2)
Newtons Laws of Motion
1) "Bodies will continue to move with a uniform velocity (which includes being stationary) unless acted on by a resultant force."
2) "Resultant force is equal to the rate of change of momentum."
This forms the basis of Newton's equation, F=ma. This equation actually comes from the idea of momentum, which can be found in the Principles of the conservation of momentum
3) "Every force has an equal and opposite force acting on another object."