Briefly explain why a conservative force does work a dissipa

Briefly explain why a conservative force does work, a dissipative force does work and constraint force DOES NOT work? Use obvious examples for each of these forces. Engineering Dynamics.

Solution

1) conservative force is force which has ability to do the work independent of path taken and it is stored in object in the form of potential energy

2)non conservative or dissipative force has ability to do work and dependent on path taken but it is not stored in obect and dissipated to surrounding and because of this non conservative forces entropy of universe is increasing

3) constraint forces are forces which are responsible for stability of body at any instant and there is no displacement in the direction of forces hence work done is zero and as displacement is in perpendicular direction it has virtual work done in perpendicular direction

4) all above force can be understand by following example of wheel moving down the slope from point A to pointB

at point A gravitational force act in downward direction and it is conservative force and it posses potential energy due to height and as wheel reaches point B it is available in kinetic form as energy was stored at A in wheel,hence conservative force does work ,independent of path as path is inclined and available to body.

where as for non conservative or dissipative for ces like friction act in oppisite direction of wheel and it does the work as wheel move down theslope and try to reduce kinetic energy of wheel and this loss of energy by friction is not going to avail to wheel at pointB,hencedissipative forces does the work ,dependent on path taken and not stored in body.

for constraint force who create stability of body that is normal reaction on wheel in upward direction keep wheel on surface of earth and as there is no dispalcement in normal direction ,work done is zero but it create virtual work via friction force in opposite direction of motion perpendicular to normal force,hence costraint force does not perform real work.