In which way is an arrangement of forces called a "couple" related to the force called "moment"?
Answer:
When a body is rotated without translation by two moments equal, parallel, opposite and noncollinear, then this arrangement of forces are called a couple.
A moment is the tendency of a force to cause rotation of a body around a fixed axis. It is one force producing a sliding vector.
Moyers, R.E. 1980. Biomechanics of tooth movements. Handbook of orthodontics. 3rd ed. London: Year Book Medical Publishers Inc. p429.
Hi Cheryl, To conclude this topic
ReplyDeleteA “couple” is two forces equal, parallel, opposite and non-collinear in producing a free vector.
A “moment” is the tendency of a force to cause rotation of a body around a fixed axis.
Given the same free body and the same force, a moment gives the same translation as if the force were applied through the centre of mass, but it also produces a rotational tendency (M =Fxd)
It is possible to rotate a body without translation by two moments that are equal, parallel in the opposite direction and non collinear = a couple.
(Translation of a tooth can be achieved if a force and two equal and opposite forces (a couple) are applied to the crown of the tooth without applying the force directly through the centre of resistance).