1. What Is the Law of Conservation of Energy?
The law of conservation of energy states that:
Energy can neither be created nor destroyed. It can only change from one form to another.
This means the total energy of a closed system always remains constant, even if energy changes forms many times.
1.1. What a Closed System Means
A closed system is one where no energy enters or leaves from outside. Energy simply transforms within the system.
2. Energy Transformations
Whenever something happens—falling, rising, stretching, heating, lighting—energy is converted from one form to another.
2.1. Common Transformations
- Potential → Kinetic (falling objects)
- Chemical → Kinetic (muscles using food energy)
- Electrical → Light (bulb glowing)
- Chemical → Heat (burning fuel)
- Light → Chemical (photosynthesis)
2.2. Energy Never Disappears
Even if energy seems ‘lost’, it has usually changed into forms like heat or sound.
3. Conservation of Mechanical Energy
When only conservative forces like gravity act, the total mechanical energy remains constant:
\( KE + PE = \text{constant} \)
3.1. What This Means
If potential energy decreases, kinetic energy increases by the same amount, and vice versa.
4. Falling Object Example
A ball falling from a height is a perfect example of energy conversion.
4.1. At the Top
High potential energy, zero kinetic energy.
4.2. During the Fall
Potential energy decreases. Kinetic energy increases.
4.3. Just Before Hitting the Ground
Potential energy is minimum. Kinetic energy is maximum.
5. Roller Coaster Example
A roller coaster converts energy back and forth as it moves along the track.
5.1. At the Highest Point
Maximum potential energy, slowest speed.
5.2. At the Lowest Point
Maximum kinetic energy, highest speed.
5.3. With No Friction
Total mechanical energy stays constant throughout the ride.
6. Why Energy Seems To Be ‘Lost’
In real-life situations, non-conservative forces such as friction and air resistance convert some mechanical energy into heat, sound, or other forms. This makes mechanical energy appear to decrease, but total energy is still conserved.
6.1. Examples
- Car engines get hot due to friction.
- Falling objects produce sound when they hit the ground.
- Machines heat up as they work.
7. Real-Life Applications of Conservation of Energy
The principle helps us understand many natural and technological processes.
7.1. Examples
- Hydroelectric dams convert potential energy of water into electricity.
- Springs store elastic potential energy and release it as kinetic energy.
- Bow and arrow systems store and release energy efficiently.