ENERGY                                                                                                GO BACK

Energy can be defined as the ability or capacity to do work.

The SI unit of Energy is same with that of Work  = Joule

Form of Energy

1. Mechanical Energy : this Energy exists in form of Kinetic and Potential energy               i  Kinetic Energy is the Energy of a moving objects, horizontally or vertically under gravity.                                                                                                                                         ii  Potential Energy is the energy a body possesses because of its position
2. Nuclear Energy: is the Energy from the nucleus of an Atom. Is the Energy in Atomic Bomb
3. Chemical Energy : is an energy in a chemical substances both organic and inorganics .such available in a battery and our food.
4. Elastic Energy : is the Energy available in an Elastic material when stretched  .
5. Electrical Energy : Is the energy use to power television and light bulb
6. Light Energy: this is the energy from Sun that makes us to see our Environment
7. Sound Energy: is the Energy from bell or loud speaker.
8. Heat Energy : is the Energy available in Hot substances.

Kinetic Energy                  

The energy in a moving object is a Kinetic Energy.

KINETIC ENERGY FORMULA

A Car of Mass m (kg) is running with a speed u(m/s) . If this car is brought to rest (v=0) at a distance s(m) with brake force of F (N) in time t(s). what is the Kinetic Energy of the car?

Work done to bring the car to rest = Force x distance  = F x s

F=ma =mu/t

Work done 

Work done = kinetic Energy

If this car start from rest  (u=0) and accelerate to velocity v(m/s)

Then the Kinetic Energy

Example

A car of  mass 20kg is moving with a speed of 5m/s . Calculate its Kinetic Energy

Solution

m= 20kg

v= 5m/s

KE

= 250J

POTENTIAL ENERGY

A stone of Mass m(kg)  at a height of h(m) above the ground possesses a potential energy.

The work done in bringing the stone to the groung level = Force x Distance =

Weight of the stone  x raised height

- mg x h= mgh

The potential Energy = mgh

This potential energy is called Gravitational Potential Energy.

in case of Elastic Potential Energy PE= 

where h is the extension and k is the elastic constant

READ now The Law of Conservation of Energy.

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