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October 4, 2010 / car.


Gravity is one of the fundamental interactions of nature, in which objects with mass attract one another. Newton’s theory of universal gravitation states that the force between any two distant bodies (m1 and m2) is F=(G\cdot m1 \cdot m2)/ r^2, where the gravitational constant G is 6.67\cdot 10^-11 N\cdot m^2 \cdot kg^-2.

So if all bodies attract each other with some force, how is it that we see astronauts on the ISS or shuttle floating as if they were in a non-gravity world?

Well, the fact is that the astronauts are in fact orbiting around the Earth, and they are in a state that we may call free fall. In this state, the spaceship is continuously falling in its trajectory around the Earth (if it were not falling, it would scape the Earth). This is easily seen with the cannon example, where we put a cannon in the top of a mountain and fire it, it the firing speed is high enough, the cannonball will orbit the Earth.

Newton's cannon explanation

Be it free fall, microgravity or other names, it is a very useful state for study of different physical, chemical and biological processes without the influence of gravity (e.g. crystal formation,…), so more to come!


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