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We have seen whenever we throw some object, after it loses the energy we gave it. It gets acceleration towards the earth as if earth is pulling it towards itself.

• This acceleration is 9.8 m/s^2 on earth, 1.6 m/s^2 on the moon, 3.7 m/s^2 on Mars etc.
• This acceleration is 0 m/s^2 in space.
  • So, if we throw some object in space, it will keep moving in the same direction. It will not come back to us.

Newton’s theory of gravity

• Newton had his theory why we feel this acceleration. He said that mass attracts mass.
  • Hence earth attracts us. So, we feel a force that pulls us towards the earth. This force is called gravity.

Einstein’s theory of gravity

• Einstein had his theory on how this force comes.
• He said that mass bends the space-time around it. So, objects are pulled towards the mass. This bending of space-time is called gravity.
  • So here even the particle with no mass is pulled towards the mass. Because mass bends the space-time around it.
• Whatever the theory of origin of this force, we found that earth & other planets pull objects towards themselves which causes acceleration. This acceleration is called gravity.