Physics Basics
Physics · भौतिकी की मूल बातें
📋Quick Overview
Physics is the study of nature and natural phenomena — how things move, why things fall, what is light, how electricity works, etc. The word 'Physics' comes from the Greek word 'Physis' meaning nature. It is the most fundamental of all sciences because its laws govern everything from atoms to galaxies.
Physics is called the 'Father of all Sciences'. Albert Einstein, Isaac Newton, and Galileo are considered the greatest physicists.
📖Branches of Physics
| Branch | Studies What |
|---|---|
| Mechanics | Motion of objects, forces, energy |
| Thermodynamics | Heat and temperature |
| Optics | Light and vision |
| Acoustics | Sound |
| Electromagnetism | Electricity and magnetism |
| Nuclear Physics | Atomic nucleus, radioactivity |
| Quantum Mechanics | Behavior of subatomic particles |
| Astrophysics | Stars, planets, universe |
📖Fundamental vs Derived Quantities
Fundamental quantities are basic quantities that do NOT depend on other quantities. There are 7 fundamental quantities. Derived quantities are made by combining fundamental quantities — like speed = distance/time.
| Fundamental Quantity | SI Unit | Symbol |
|---|---|---|
| Length | Meter | m |
| Mass | Kilogram | kg |
| Time | Second | s |
| Electric Current | Ampere | A |
| Temperature | Kelvin | K |
| Amount of Substance | Mole | mol |
| Luminous Intensity | Candela | cd |
📖Scalar vs Vector Quantities
Simple trick: If someone asks 'which direction?' and it makes sense to answer, it's a VECTOR. If direction doesn't matter, it's a SCALAR. Example: 'I weigh 60 kg' — direction doesn't matter → Scalar. 'The wind blows at 50 km/h towards east' — direction matters → Vector.
📝Measurement & Units
- •Measurement = comparing an unknown quantity with a standard (unit)
- •Three main systems: CGS (centimeter-gram-second), MKS (meter-kilogram-second), FPS (foot-pound-second)
- •SI system (International System) adopted in 1960 — based on MKS system — used worldwide
- •1 light year = distance light travels in 1 year = 9.46 × 10¹² km (used for astronomical distances)
- •1 Astronomical Unit (AU) = distance from Earth to Sun = ~15 crore km
- •Parsec is the largest unit of distance (1 parsec = 3.26 light years)