Introduction
Gravitation is the force of attraction between any two objects having mass. It explains why objects fall towards the Earth and how planets move around the Sun.
Universal Law of Gravitation
Every object in the universe attracts every other object with a force that is:
- Directly proportional to the product of their masses
- Inversely proportional to the square of the distance between them
Formula:
F=Gr2m1m2
Where:
F = gravitational force
G = universal gravitational constant
m₁, m₂ = masses of objects
r = distance between their centers
Importance of Gravitation
- Keeps planets in orbit
- Causes objects to fall on Earth
- Responsible for tides
- Holds atmosphere around Earth
Free Fall
- Motion of an object under the influence of gravity only.
- Acceleration during free fall is constant.
Acceleration Due to Gravity (g)
- Acceleration of an object falling freely towards Earth.
- Value on Earth = 9.8 m/s²
- Always acts towards the center of Earth.
Difference Between Mass and Weight
| Mass | Weight |
|---|---|
| Amount of matter | Force of gravity on mass |
| Constant everywhere | Varies from place to place |
| SI unit: kg | SI unit: newton |
| Scalar quantity | Vector quantity |
Weight
- Weight = mass × gravity
W=mg
Thrust and Pressure
Thrust
- Force acting perpendicular to a surface.
Pressure
- Force per unit area.
Pressure=AreaForce
Pressure in Fluids
- Pressure increases with depth.
- Liquids exert pressure in all directions.
Buoyancy
- Upward force exerted by a fluid on an object immersed in it.
- Helps objects float.
Archimedes’ Principle
An object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced.
Applications of Archimedes’ Principle
- Designing ships and submarines
- Hydrometers
- Determining purity of metals
Quick Short Q&A (Most Possible)
| Question | Short Answer |
|---|---|
| What is gravitation? | Force of attraction between masses |
| Who gave law of gravitation? | Newton |
| Formula of gravitation? | F = Gm₁m₂ / r² |
| Value of g on Earth? | 9.8 m/s² |
| Free fall means? | Motion under gravity only |
| Weight formula? | W = mg |
| Unit of pressure? | Pascal |
| Buoyancy definition? | Upward force by fluid |
| Archimedes’ principle? | Buoyant force = weight of displaced fluid |
| Mass vs weight difference? | Mass constant, weight varies |