๐ง Work
Work is said to be done when a force applied on an object causes the object to move in the direction of the force.
Work (W) = Force (F) ร Distance (d) ร cos ฮธ
- SI unit of work: Joule (J). 1 J = 1 N ร 1 m.
- Work is a scalar quantity.
- Positive work: Force and displacement are in the same direction (e.g. lifting a box).
- Negative work: Force and displacement are in opposite directions (e.g. friction opposing motion).
- Zero work: Force is perpendicular to displacement (e.g. carrying a bag horizontally), or object does not move.
โก Power
Power is the rate at which work is done.
Power (P) = Work Done (W) รท Time (t)
- SI unit of power: Watt (W). 1 W = 1 J/s.
- Larger unit: kilowatt (kW) = 1000 W; used for engines and appliances.
- Horsepower (HP): 1 HP โ 746 W (used for motors and vehicle engines).
๐ Energy
Energy is the capacity to do work. It is a scalar quantity. SI unit: Joule (J).
Kinetic Energy (KE)
Energy possessed by an object due to its motion.
KE = ยฝ ร m ร vยฒ
- m = mass (kg), v = velocity (m/s)
- KE increases with speed (proportional to vยฒ).
Potential Energy (PE)
Energy stored in an object due to its position or state.
Gravitational PE = m ร g ร h
- m = mass (kg), g โ 10 m/sยฒ, h = height above ground (m).
- Types: gravitational PE, elastic PE (stretched spring/rubber band), chemical PE.
๐ Forms of Energy
| Form | Description & Example |
|---|---|
| Heat Energy | Energy due to temperature; e.g. burning fuel, friction |
| Light Energy | Energy carried by electromagnetic radiation; e.g. sunlight |
| Sound Energy | Energy of vibrating particles; e.g. a ringing bell |
| Chemical Energy | Stored in chemical bonds; e.g. food, fuels, batteries |
| Electrical Energy | Energy of moving charges; e.g. electric current in a wire |
| Nuclear Energy | Released in nuclear reactions; e.g. nuclear power plants, the Sun |
| Mechanical Energy | Sum of kinetic and potential energy of an object |
๐ Law of Conservation of Energy
Law of Conservation of Energy: Energy can neither be created nor destroyed. It can only be converted from one form to another. The total energy of an isolated system remains constant.
Common Energy Transformations
- A falling stone: Gravitational PE โ Kinetic Energy
- An electric bulb: Electrical energy โ Light energy + Heat energy
- A microphone: Sound energy โ Electrical energy
- A solar panel: Light energy โ Electrical energy
- A battery: Chemical energy โ Electrical energy
- A steam engine: Heat energy โ Mechanical (kinetic) energy
๐ฑ Sources of Energy
| Renewable Sources | Non-Renewable Sources |
|---|---|
| Solar energy | Coal |
| Wind energy | Petroleum (Oil) |
| Hydropower (water) | Natural gas |
| Biomass/biogas | Nuclear fuels (uranium) |
| Tidal and wave energy | |
| Geothermal energy |
- Renewable: Replenished naturally; will not run out; generally less polluting.
- Non-renewable: Formed over millions of years; limited supply; burning them produces greenhouse gases.
๐ท๏ธ Key Terms
Work
Joule
Power
Watt
Energy
Kinetic energy
Potential energy
Mechanical energy
Chemical energy
Conservation of energy
Energy transformation
Renewable energy
Non-renewable energy
Fossil fuels