1. What Is Energy?
Energy is the ability of an object to do work. Whenever something moves, heats up, lights up, or produces sound, energy is involved.
Energy helps us understand how objects change their state — whether they speed up, rise, fall, stretch or heat up.
1.1. Energy Makes Change Possible
Without energy, no work can be done. A moving vehicle, a running fan, a ringing phone — all require energy to function.
2. Different Forms of Energy
Energy appears in many forms. Even though these forms look different, they can convert from one form to another.
2.1. Common Forms of Energy
- Kinetic energy — energy of motion.
- Potential energy — stored energy due to position.
- Chemical energy — stored in food, fuels, batteries.
- Electrical energy — used in appliances and machines.
- Heat energy — energy due to temperature.
- Light energy — energy that helps us see.
2.2. Energy Can Change Forms
Examples of energy conversion:
- A battery (chemical energy) powers a torch (light energy).
- A car engine converts fuel (chemical energy) into motion (kinetic energy).
- A falling object converts potential energy into kinetic energy.
3. Units of Energy
The SI unit of energy is the Joule (J).
1 Joule is the energy transferred when 1 Newton of force moves an object by 1 metre.
3.1. Larger Units
- Kilojoule (kJ) = 1000 J
- Megajoule (MJ) = 1,000,000 J
3.2. Everyday Understanding
A small apple has about 300 kJ of chemical energy. A 60-watt bulb uses 60 J of electrical energy every second.
4. Mechanical Energy
Mechanical energy is the combined energy of motion and position:
\( E_{mechanical} = KE + PE \)
This form of energy appears in many moving systems.
4.1. Examples
- A swinging pendulum has kinetic energy at low points and potential energy at high points.
- A moving car on a hill has both kinetic and potential energy.
5. Energy in Everyday Life
Energy is everywhere around us. Every action you see involves energy transformations.
5.1. Examples
- Eating food gives your body chemical energy.
- Solar panels convert sunlight into electrical energy.
- Fans convert electrical energy into kinetic energy of air.
- Burning fuel releases heat and light energy.