Class 9 Science Solutions English Medium

Energy and its Forms

Energy: The Capacity of doing work is known as energy.

Energy is a scaler quantity. 

S.I unit of energy is joule (J) and biggest unit is kilo Joule (kj) 

                      1 kJ = 1000 J 

• Life is impossible without energy.
• The demand for energy is ever increasing.
• The Sun is the biggest natural source of energy to us.
• Many of our energy sources are derived from the Sun.
• We can also get energy from the nuclei of atoms, the interior of the earth, and the tides.

Energy possess object:

- An object having a capability to do work is said to possess energy.

- The object which does the work loses energy and the object on which
the work is done gains energy.

How does work happens by using Energy? 

An object that possesses energy can exert a force on another object. When this happens, energy is transferred from the former to the latter. The second object may move as it receives energy and therefore do some work. Thus, the first object had a capacity to do work. This implies that any object that possesses energy can do work.

The capacity of doing work is  measured in Joule. 

Forms of Energy: 

There are different forms of energy: 

(1) Mechanical Energy: The sum of potential energy and kinetic energy is called mechanical energy. 

 Mechanical Energy = Potential Enrgy + Kinetic Enrgy 

In other words: The energy possess by a body on Account of its potition or motion is called mechanical energy.  

     (i) Potential Energy: The energy possessed by the object is the energy present in it by virtue of its position or configuration is called potential energy. 

     Or   The stored energy in an object due to change in its position is called potential energy. 

     (ii) Kinetic Energy: The energy possess by an object due to its motion is called kinetic energy. 

(2) Sound Energy : The energy possess an object during vibration and produce sound such energy is called sound energy. Sound energy has capacity to do work.   

(3) Heat Energy: Heat is also an energy. When a matter is heated its tiny particles vibrate or move. it has capacity to do work. 

(4) Chemical Energy: The energy released or produced during chemical reactions is called chemical energy. 

(5) Electrical Energy: Electrical energy is a form of energy resulting from the flow of electric charge. Electric energy has ability to do work or apply force to move an object. The force is electrical attraction or repulsion between charged particles.

(6) Light/Solar Energy: The sun is the begest source of energy on the Earth. We use the sunlight as energy. 

(7) Nuclear Energy: The energy released by fussion and fission of nucleuos of an atom is called nuclear energy.