Work and Energy – Work
* Work done by force acting on an object is equal to the magnitude of the force multiplied by the displacement of the object in the direction of the force.
Condition for work to be done:
* A net force act on an object.
* The object must be displaced in the direction of the net force.
* Definition of work: Work is said to be done when an object is displaced on applying a certain force.
* Work done is the product of force and displacement: (W = F x s)
* Work is measured in joule in the SI system. One (j) is the work done when the net force of one newton acts on body and displaces in the direction of the force by the metre.
* Work in the CGS system is measured on erg. One is the work done when the net force of one dyne acts on a body and displaces it in the direction of the force by one centimetre.
* The work done on the object is independent of the path transverse by the object.
* Work done is a scalar.
Work done can be either positive or negative:
* Work done is positive if the force applied and the displacement, both are in the same direction.
* Work done is negative when the force acts in a direction opposite to the direction of displacement.
Work and Energy – Energy
* Energy is defined as the capacity to do work.
* The various forms of energy include kinetic energy, potential energy, light energy, thermal or heat energy, electrical energy and chemical
energy.
* Energy stored in an object due to its position or place is known as potential energy.
* The gravitational potential energy of an object is the work done in raising it from the ground to a certain point against gravity. it is
calculated using the expression PE=mgh.
* The energy possessed in a moving object is called kinetic energy. it is calculated by the formula:
EK= ½ mv2
Where,
m is the mass of the object
v is the velocity of the object
* Energy can be converted from one form to another.
* Law of conservation of energy: energy can neither be created nor destroyed, but can change its form.
* Power (P) is the rate of doing work.
* It is calculated using the expression:
P = W/t
Where,
W is the work done
t is the time taken
We express larger rates of energy transfer in kilowatts (kW).
Conservation of Energy: Simple Pendulum
* Energy exists in several forms and can be converted from one form into another, but it cannot be destroyed. This is called the conservation
of energy.
* The total mechanical energy in a system is the sum of its PE and KE.