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TOPIC: FORCE

SUB-TOPIC: GRAVITATION AND WEIGHTLESSNESS

Meaning of gravitation:

Gravitation is a type of force that acts on a body across a distance, without any contact between the source and the body.

The earth exerts a gravitational force on bodies by which it pulls these bodies towards its centre. This is why fruits fall to the ground from the tree and do not rise upwards. Also, when a stone is thrown upwards it soon stops its upward movement and starts to fall back to the earth.

The force of gravity is a universal force. It exists between the earth and bodies and between planets and stars.

Gravitational pull determines the weight of objects.

The amount of force with which gravity pulls an object depends on three things:

  1. The mass of the object.
  2. The mass of the earth.

iii. The distance between the centre of the object and the earth.

Effect of gravitation on objects:

  1. Gravitation gives objects weight.
  2. Gravitation keeps the earth and the other planet in their orbits around the sun.
  3. Gravitation keeps the moon in its orbits around the earth.
  4. Gravitation keeps the moon in its path in the sky.
  5. It is the work against gravity that make aero plane to fly in the sky.
  6. Gravitation bring about the formation of tides, for convection (by which hot fluids rise)
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 WEIGHTLESSNESS:

The term weightlessness is described as a state of not experiencing the effect of gravity. Astronauts in space experience weightlessness. It does not mean that they do not have weight but they will just feel as if they are weightless. Weightlessness is felt in space and moon. The weight of an object in the moon is one sixth () of the weight of the object on earth. If an astronaut weighs 60N on earth, in the moon he will weigh 10.

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