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Introduction
Have you ever wondered why your arms feel tired after carrying a heavy school bag? Or why machines make our life easier? Or even how electricity bills are calculated?
All these questions connect to three key ideas in physics: Work, Power, and Energy.
These are not just textbook terms. They explain how effort is applied, how energy is used, and how fast things are done—whether you’re pushing a swing, turning on a light, or pedaling a bicycle.
Let’s break it down in a simple way—step by step, with relatable examples, clear formulas, and real-world connections.
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What is Work in Physics?
In everyday life, we say “I’m doing work” when we’re busy. But in physics, the meaning is very specific.
Work is done when:
- A force is applied on an object
- The object moves in the direction of the force
No movement = No work (in physics)
Even if you’re holding something heavy, if it doesn’t move, no work is done in the physics sense.
Formula:
Work (W) = Force (F) × Displacement (d)
(Unit: Joule, symbol J)
1 Joule = 1 Newton × 1 meter
Examples:
- Lifting a box → Work is done
- Pushing a door open → Work is done
- Holding a bag still → No work (no displacement)
- Carrying a suitcase vertically while walking horizontally → No work in direction of motion
What is Energy?
Energy is the ability to do work. Every moving object, electric device, or even a person at rest has energy.
Main Types of Energy:
1. Kinetic Energy (KE)
Energy a body has because it’s moving
Formula:
KE = ½ × m × v²
Where m = mass, v = velocity
2. Potential Energy (PE)
Stored energy due to position or height
Formula:
PE = m × g × h
Where g = 9.8 m/s² (acceleration due to gravity), h = height
Units:
Same as work → Joule (J)
Real-Life Examples:
- A moving car → Kinetic Energy
- A stretched rubber band → Potential Energy
- Water stored in a dam → Potential Energy
What is Power?
Power tells us how fast work is done or how quickly energy is used.
Formula:
Power (P) = Work done (W) / Time taken (t)
SI Unit: Watt (W)
1 Watt = 1 Joule per second
More practical units:
- 1 kilowatt (kW) = 1000 W
- 1 horsepower (hp) = 746 W
- 1 kilowatt-hour (kWh) = Energy used by a 1000 W device in 1 hour
Real-Life Example:
- A 100W bulb uses 100 Joules every second
- A more powerful machine does the same work in less time
Energy Transformation
Energy is never destroyed—it just changes form. This is called the Law of Conservation of Energy.
Examples:
- Electric energy → Light + Heat (in a bulb)
- Chemical energy → Kinetic (in a car engine)
- Potential → Kinetic (in a falling object)
- Solar energy → Electrical (in solar panels)
Summary Table of Core Concepts
| Term | Meaning |
| Work (W) | Force × Displacement |
| Energy | Ability to do work |
| Power (P) | Work ÷ Time |
| Kinetic Energy (KE) | Energy of motion |
| Potential Energy | Stored energy due to position |
| Joule (J) | Unit of work or energy |
| Watt (W) | Unit of power (1 W = 1 J/s) |
| kWh | 1000 watts used for 1 hour |
Real-Life Applications
In Everyday Life:
- Climbing stairs → Work done
- Running → Uses energy
- Lifting a bag faster → More power
At Home:
- Electricity bills use kWh
- A refrigerator rated 300W uses 0.3 kWh in 1 hour
- A microwave at 1000W uses 1 kWh in 1 hour
In Science & Engineering:
- Rockets need huge amounts of energy
- Machines are rated by their power output
- Engineers design motors by calculating work and power
Frequently Asked Questions
Q1. What must happen for work to be done?
An object must move in the direction of applied force.
Q2. What is the unit of energy?
Joule (J), same as work.
Q3. Is holding something work in physics?
No, because there’s no displacement.
Q4. What is 1 kilowatt-hour?
It’s the energy used by a 1000 W appliance in 1 hour.
Used in electric bills.
Q5. What’s the difference between energy and power?
Energy is total work done; power is how fast that work is done.
Fun Facts
- A healthy human at rest uses around 100 watts of power—same as a small light bulb!
- One horsepower = 746 watts. That’s how strong one horse is.
- The Sun gives off around 3.8 × 10²⁶ Joules of energy per second.
- Lifting a 1 kg object by 1 meter takes about 10 joules of energy.
Conclusion
Work, Power, and Energy are the hidden forces behind every action we take and every machine we use.
From simple acts like climbing stairs to complex systems like rocket launches, these three concepts explain how things move, how much energy is needed, and how quickly it happens.
Once you understand them, you won’t just be memorizing formulas—you’ll start seeing physics everywhere: in your body, your home, your devices, and the world around you.
