Page 26 - mechanics

Chapter – 5 Equilibrium of rigid body & Reactions of supports

5.1 Reactions of Supports
The question arises here, How come you can easily open a door
(rotate it) and you cannot pull it away from the wall? Why you
cannot neither move nor rotate a light pole on the street?

Fig. 5.1 Different effects for different supports.

The basic function of a support is to prevent motion
(translation or rotation) of the body by attaching the body in a
certain way to its surroundings. Each support has its way of
supporting the body and thus each support has its own use.

Consider the case when you push a body along a certain
direction yet it is prevented by its support. This means that the
support exerts on the body an opposite force to the force you
exerted. In the same manner, if a body is subjected to a couple
moment yet it does not rotate due to its support, this means that
this support induces a reverse moment to create a balance of

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