A comparative study between Non-Conservative and Conservative force
Here we will discuss about two types of forces namely conservative forces and non conservative forces. So how do they differ? Consider following two situations as shown in the figure
In figure 1, when the mass comes to rest, the spring gets compressed by a distance ‘x’. The spring then comes to its normal length and mass attains a velocity ‘v’. This compression and elongation continues and each time with a maximum value of ‘x’. So we can infer that the total mechanical energy of the system (Block + Spring) remains constant. While in the second case also there will be compression and elongation but the minimum value will keep on decreasing. So we can say that the total mechanical energy of the system is not conserved in this case.
From our observations in the above case we can now define conservative and non-conservative forces. A conservative force is a force that does zero work done in a closed path. If only these forces act then the mechanical energy of the system remains conserved. Examples of conservative force : Gravitational force, spring force etc.
On the other hand non-conservative forces are those forces which cause loss of mechanical energy from the system. In the above case friction is the non-conservative force. But as we know energy can neither created nor destroyed hence these forces convert mechanical energy into heat, sound, light etc.
Now, Conservative force has one more property that work done by it is independent of the path taken.
Work done by conservative force
Consider the following scenario
In figure one we know work done by conservative force in a closed path is zero.
W1, A, B + W2, B, A = 0
W1, A, B = – W2, B, A
We also have,
W2, B, A = – W2, A, B
Using the above two equations we get,
W1, A, B = W2, A, B
The above equation shows that work done to move a particle from point A to B through path 1 and 2 as shown in figure 2 will take same amount of work done. But this statement is not valid for non-conservative forces.
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