Energy is present in many different forms depending on how an object behaves.
Energy is the ability or capacity of an object or system to do work or bring about a change.
Energy cannot be seen directly, but its effects can be observed whenever an object moves, changes position, produces heat, light, or sound.
Forms of Energy:
Energy exists in different forms. Each form of energy can be converted into another.
| Form of Energy | Description | Example |
|---|---|---|
| Mechanical Energy | Energy due its motion or position | Moving bicycle |
| Heat Energy | Energy transferred due to temperature difference | Boiling water |
| Light Energy | Energy that enables us to see | Sunlight |
| Sound Energy | Energy produced by vibrating objects | Ringing bell |
| Electrical Energy | Energy carried by electric current | Electric fan |
| Chemical Energy | Energy stored in food, fuels and batteries | Petrol, food |
| Nuclear Energy | Energy stored inside the nucleus of atom | Nuclear power plant |
Mechanical Energy:
Mechanical energy is one of the most common forms of energy.
Mechanical energy is the total energy possessed by an object due to its motion and position.
It consists of
- Kinetic Energy
- Potential Energy
Therefore,
\(Mechanical\ Energy\ =\ Kinetic\ Energy\ +\ Potential\ Energy\)
Kinetic Energy
Kinetic energy is the energy possessed by an object because of its motion.
Any object that is moving has kinetic energy.
Example:
Moving train
Running athlete
Rolling football
Flying aeroplane
Kinetic energy depends on:
- Mass of the object
- Velocity (speed) of the object
Formula:
\(KE=\frac{1}{2}mv^{2}\)
Where
- \(KE\ =\ Kinetic\ Energy\)
- \(m\ =\ Mass\)
- \(v\ =\ Velocity\)
Important Observations
- Greater mass \(\to\) Greater kinetic energy
- Greater velocity \(\to\) Much greater kinetic energy
- If velocity becomes zero, kinetic energy also becomes zero.
Potential Energy:
Potential energy is the energy possessed by an object due to its position or configuration.
It is called "stored energy."
Example:
Water stored behind a dam
Book placed on a shelf
Coconut hanging on a tree
Child standing on a diving board
Gravitational Potential Energy:
Gravitational potential energy is the energy possessed by an object because it is at a height above the Earth's surface.
\(PE\ =\ mgh\)
Where
- \(PE\ =\ Potential\ Energy\)
- \(m\ =\ Mass\)
- \(g\ =\ Acceleration\ due\ to\ gravity\)
- \(h\ =\ Height\)
Factors Affecting Potential Energy:
Potential energy depends on
- Mass
- Height
- Gravity
Important Points
- Greater height \(\to\) Greater potential energy
- Greater mass \(\to\) Greater potential energy
- If height is zero, gravitational potential energy becomes zero.
Conversion Between Potential and Kinetic Energy:
Energy continuously changes from one form to another.
Example - Falling Ball
At the top:
- Maximum Potential Energy
- Minimum Kinetic Energy
While falling:
- Potential Energy decreases
- Kinetic Energy increases
Just before touching the ground:
- Maximum Kinetic Energy
- Minimum Potential Energy
Law of Conservation of Mechanical Energy:
The total mechanical energy of an object remains constant if only conservative forces (such as gravity) act on it and friction or air resistance is neglected.
This means
\(Potential\ Energy\ +\ Kinetic\ Energy\ =\ Constant\)
Although kinetic energy and potential energy keep changing individually, their total remains constant.