Conservative Force and Non-Conservative Force

In previous blog, we have discussed that whenever one form of energy disappears, an equivalent energy appears in some other forms. In here Conservative Force and Non-Conservative Force we discuss. Some of these new forms of energy can be retraced in their previous forms while others can’t be retraced.

For example ; when you throw a ball vertically upwards, its K.E. gradually decreases due to decrease in velocity and attains a minimum value of zero at maximum height.

Here, the loss in K.E. appears in the form of P.E. which gradually increases and attains a maximum value at maximum height. However, as the ball falls down, the P.E. is gradually decreased and this loss in P.E. reappears as the K.E.

In other words, we can say that, loss in one form of energy is stored as another form so that an equivalent amount of energy can be retrieved in its original form. A force that offers an opportunity of two way conversion between kinetic and potential energies is called Conservative force.

An essential feature of conservative force is that, their work done is always reversible. Anything that is deposited in any form of energy (P.E. or K.E.) can later be withdrawn without loss i.e., total mechanical energy is always conserved. The work done by such forces are independent of actual path followed but depend only on the initial and final position.

However, when the starting and ending points are same, the total work done is zero i.e., total work done round a closed path is always zero. In contradiction, all the forces are not conservative.

Consider a body is sliding over a rough surface under the action of applied force. In this case, as the body slides, frictional force appears in the direction opposite to objects displacement and does negative work.

Similarly, if the body now moves opposite to its previous direction, the frictional force again, appears opposite to object’s displacement and again does negative work. In this way, in both situations, the net work done by applied force is reduced. This means there is loss in K.E. of the body which can’t be retrieved even if we reverse its path.

The loss in K.E. appears in the form of heat, light, sound etc. Such forces for which the work done is not reversible are called non conservative forces. These forces are path dependent and whenever any form of energy (K.E. or P.E.) is lost, it is lost forever in some other forms. The original form of energy (P.E. or K.E.) can’t be retrieved i.e.,total mechanical energy is not conserved.

However, the non-conservative force doesn’t always cause the loss of mechanical energies.

There are also non-conservative forces that increase mechanical energy. For example, the fragments of an exploding fire cracker fly off with very large kinetic energy which is due to the chemical reaction of gun powder with oxygen i.e., the chemical energy of gun powder aids the increase of K.E of fragments.

The examples of conservative forces are gravitational force, electric force, spring forces, magnetic forces etc and that of non-conservative force are kinetic friction, fluid resistance etc.

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