Work and Energy
Work is done when force acting on a body produces displacement in it.
Work done = Force × displacement in the direction of force
Work is a scalar quantity.
The SI unit of work is joule (j).
Work done is positive if the angle between force and displacement is acute.
Work done is negative if the angle between force and displacement is obtuse.
Work done on an object by a force would be zero if the displacement of the object is zero.
When a body moves along a circular path, the force acts along the radius of the circular path and the motion of the body is along the tangential direction. Therefore, the angle between the direction of motion and the force is 90°. Hence, no work is done on a body when it moves in a circular path.
An object having a capability to do work is said to possess energy.
The energy possessed by a body by virtue of its motion is called kinetic energy.
The energy possessed by a body by virtue of its position or change in configuration is called potential energy.
Power is defined as the rate at which work is done.
The change of one form of energy into another is called transformation of energy.
Law of conservation of energy states that energy can neither be created nor be destroyed but can be transformed from one form to another.
Energy exists in nature in several forms such as kinetic energy, potential energy, heat energy, chemical energy etc. The sum of the kinetic and potential energies of an object is called its mechanical energy.
The energy used in one hour at the rate of 1kW is called 1 kW h.
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NCERT 9 Science