- Mechanical energy
The energy possessed by a body due to its position or motion is called mechanical energy.
Mechanical energy is of two types:-
i) Kinetic energy
Energy possessed by a body by virtue of its motion is called kinetic energy.it is measured by the amount of work which the body can due to its motion. The two types of K.E. are as follows:
- Kinetic energy of translation: Kinetic energy due to rectilinear motion of a body is called Kinetic energy of translation.
e.g., a car moving on a road, a moving bullet, water moving on a stream etc.
Consider a mass (m) which is initially at rest (i.e. u = 0). If a constant force F is applied, it starts moving and let the mass attains the velocity (v) after travelling a distances, Then
This work done is stored in the body in the form of kinetic energy of translation.
- Kinetic energy of rotation. The kinetic energy due to rotary motion of the body is called kinetic energy of rotation. E.g. a fly wheel rotating about its axis.
Consider a body mass m ,rotating about an axis O. Let the body is composed of elemental masses m1,m2,m3…….. etc. Situated at distances r1,r2,r3…….. etc. From the center O as shown in the figure and let the linear velocities of these masses be v1,v2,v3……….respectively. Let w be the angular velocity of the body. Then
Where, I = mass moment of inertia of the body about an axis passing through O.
(ii) Potential energy. The energy possessed by body virtue of its position is called potential energy.
The potential energy of a body is measured by the work done against conservative forces acting on the body in bridging the body from sum reference or datum position to the position in the question.
The most common form of potential energy is gravitational potential energy which is the energy possesses by a body due to its position with respect to the surface of earth. All bodies on the surface of earth have been supposed to possess zero potential energy.
If m is the mass of a body held at a height of h from earth surface, than the potential energy posses by the body is mgh.