Download Physics Work, Energy and Power

Physics
Work, Energy and Power
Work
An object which has the ability to do work is said to have energy.
Work is done: things which happen whenever energy transfer takes place.
W=F x d
Energy and Work are measured in Joules.
Energy
The energy requires by objects on which work is done is known as mechanical energy. Mechanical energy is energy
possessed by an object due to: Potential Energy (stored energy) and Kinetic Energy (motion).
Potential Energy
We know, Potential Energy is stored energy:
We will focus on 2 types of PE (EP)1) Gravitational Potential Energy and
2) Elastic Potential Energy
Elastic Potential Energy
The amount of potential energy stored in materials is related to the extent of deformation of these materials. The more
the stretch or the greater the compression, the greater the elastic potential energy stored.
Deformation is described as plastic if the atoms or molecules of the material do not return to their equilibrium positions
when the deforming force is removed.
Deformation is elastic if the atoms or molecules return to their original positions when the deforming forces are
removed.
Hooke’s Law states that extension is directly proportional to load or applied force, provided the elastic limit is not
exceeded.
Kinetic Energy
Kinetic energy is the energy than an object has because it is moving.
Relationship between Potential Energy and Kinetic Energy
Consider a ball of mass 10kg was held above the ground at 80m (gravity- 10 m/s2). If the object is released and as it falls
the gravity potential energy decreases (height) as its kinetic energy increases (speed). Find velocity?
PE
=
KE
m . g . h = ½ m . v2
10 . 10 . 80 =
40 m/s =
½ 10. v2
v
The kinetic energy with which an object strikes the ground is dissipated as heat, sound, etc. This is an example of the
principle of conservation of energy which may be stated as follows:
Energy is neither created nor destroyed, only converted to another form. Therefore, the total energy present at every
stage in a chain of energy conversations is the same.
Power
Power is the work done or energy converted per unit time. (Unit- W, watts).
Power = Force (N) x Displacement (m)
Time (s)