Mechanical Forms of Work

In elementary mechanics, the work done by a constant force F on a body a displaced s in the direction of the force given by w=Fs (kJ) (2-21)

If the force F is not constant, the work done is obtained by adding(i.e., integrating) the differential accounts of work, w=2/1 ∫ (F*ds)(kJ) (2-22)

Signs can be easily determined from the physical conditions:

1.       The work done on a system by an external force acting in the direction of motion is negative.

2.       Movement done on a system against an external force acting in the opposite direction to motion is positive.

The two requirements for a work interaction between a work system and its surroundings to exist:

1.       There must be a force acting on the boundary.

2.       The boundary must move.

No-Nos:

1.       The presence of forces on the boundary without any displacement on the boundary doesn’t constitute as work interaction.

2.       The displacement of the boundary without any force to oppose on drive this motion is not work interaction, since no energy is transferred

Mechanical Work is associated with the movement of the boundaries of a system or with the movement of the entire system as a whole

A few common forms of Mechanical Work Are:

Shaft Work

Spring Work

Work done on Elastic Bars