Why do astronauts float in Space?

Everyone has fantasized about going to Space and floating around in a spaceship! Floating in Space is fun but astronauts perform many tasks in the Space station such as fixing bolts, wires,etc which can also float if not handled carefully and hence can create trouble sometimes!
The major misconception that many have about astronauts floating in Space is that- "There is no gravity. That is why astronauts float around in the Space station." The reason why cosmonauts experience weightlessness in Space is not because there is "zero-gravity". The reason is something different and interesting. Let us learn it here:

Consider a cannon shooting cannonball:
If the ball is launched by the cannon at low speed, the ball will travel straight for some time but hit the ground in sometime.
If the speed of ball is increased, it will travel a longer distance befre hitting the ground.
If the ball is fired at a sufficient speed that it falls to the Earth but the speed of the ball keeps it from missing it. The ball will then perform a circular motion around the Earth.

Such is the case of the Space Station. The International Space Station is at an altitude of 400km. At this altitude the value of acceleration due to gravity has only dropped to 8.75 m/s^2  as compared to the value 9.81m/s^2 on the Earth surface and saying that there is zero-gravity at the Space Station makes no sense. The Space station at this altitude is falling towards Earth and is in a free-fall but misses falling just because it has sufficient speed as explained above using an example of a cannonball.

You must have experienced this free-fall even at amusement parks. When the ride reaches to a great height and suddenly drops down. You lose contact with the seat. You are in a "free-fall" similar to the astronauts. The only difference is that astronauts are at a very huge altitude as compared to the ride and in a continuous free-fall which makes them lose contact with the surface of the vehicle.

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