**Principle of Conservation of Energy**

According to this principle, energy of an isolated system is constant. In other words, "The energy can neither be created nor be destroyed but can be transformed from one form to another".

**Energy conservation for freely falling bodies:**

The mechanical energy of a freely falling body is constant. Prove.

Let a body of mass ‘m’ at point A at a height of H from the ground. Let the body fall from height. Let B be any instant point between A and C at distance x from a. Then its height from the ground is (h-x). Let C be the ground level and its height is 0.

**At A,**

**At B,**

_{b}, then

_{b}

^{2}……… (i)

^{2}= u

^{2}+ 2as

_{b}

^{2}= 0 + 2gx, where ‘g’ is the acceleration due to gravity and x is the distance traveled by the body from A to B

_{b}

^{2}= 2gx

_{b}

^{2}

**At point C,**

_{c}

^{2}……. (ii), where v

_{c}is the velocity at point C

^{2}= u

^{2}+ 2as

_{c}

^{2}= 0 + 2gH

_{c}

^{2}= 2gH

From this, we can conclude that the total mechanical energy remains same at all the points during the journey since equations (i), (ii), and (iii) are equal.

**Conservative and non-conservative forces**

A force is said to be **conservative** if the work done by or against the force in moving body depends upon only the initial and final positions of the body i.e. the distance between those bodies. If the work done by the body while bringing it into a round circle at same point, then the force applied on it is called conservative force.

A force is said to be **non-conservative** if work done by or against the force on a moving body from one position to another depends upon the path followed by the body.

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