Gravitation is the natural force by which every object with mass attracts every other object. Sir Isaac Newton gave the Universal Law of Gravitation. This concept explains why objects fall to the ground and how planets orbit the Sun.
Universal Law of Gravitation
- Every body attracts every other body with a force.
- The force is directly proportional to the product of their masses.
- It is inversely proportional to the square of the distance between them.
- The gravitational constant G = 6.67 x 10 to power -11 N m squared per kg squared.
Acceleration Due to Gravity (g)
- Average value of g = 9.8 metre per second squared.
- The value of g is maximum at the poles and minimum at the equator.
- g decreases with height and with depth below the surface.
- g becomes zero at the centre of the Earth.
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Mass and Weight
- Mass is the amount of matter; it stays the same everywhere.
- Weight = mass x g; it changes with location.
- Weight on the Moon is about one-sixth of that on Earth.
- Mass is measured in kg; weight in newton.
Escape Velocity
- Escape velocity is the minimum speed needed to leave Earth's gravity.
- Its value for Earth is about 11.2 km per second.
Quick Revision Points
- Universal law given by Newton.
- Force is inversely proportional to square of distance.
- Value of g = 9.8 m/s squared.
- g is maximum at poles, minimum at equator.
- g is zero at the centre of the Earth.
- Weight on Moon = 1/6 of Earth.
- Escape velocity of Earth = 11.2 km/s.