Astronauts float not because there is no gravity

We have all seen that astronauts float in space. They experience a state of  weightlessness which is pretty cool. However there is a wide spread misconception that astronauts float because there is no gravity in space. As the title of this article indicates, there IS gravity in orbital space and lack of gravitational pull is NOT the reason why astronauts float.

Gravity is not the reason:
Before we get into why they float, lets convince ourselves that astronauts experience almost as much gravitational force as we on the surface of the planet do. 

For the uninitiated, every object with mass attracts every other object with mass in the universe, no matter where they are located. (Off topic, it is still a mystery what causes gravitational attraction. We know it exists and we know how to measure it, but what causes it remains unknown). There is a way to calculate the gravitational pull between two objects using the following formula -

where G is a universal gravitation constant
                                    M1 and m2 are the masses of the objects in question
                   r is the distance between the two objects

Now consider the fact that the radius of Earth is approximately 6378 kilometers and that the average orbit height is 360 kilometers. Simple calculation shows that Earth's gravitational pull on a person in orbit is nearly 90% of what it is on the surface. 

Just 10% less gravity is not going to make you weight less. Thus we have established that astronauts don't float because of lack of gravity. 

So why do they float?
Alright, but why do they float? We have definitely seen them floating.

Well, astronauts are not actually floating but they are falling! The astronaut and the shuttle they are in, are in a free fall motion towards Earth because of Earth's gravitational attraction on the shuttle. This free fall is what makes the astronauts experience weightlessness. 

It is easier to wrap ones head around this by drawing an analogy with an elevator. Ever observed what happens when an elevator starts going down? We experience a little reduction in weight because the elevator is accelerating downwards and thus the force with which the floor pushes us decreases (The floor doesn't need to push you that hard because now it is getting help from gravity on your way downwards. However when the elevator is going up, it should fight against gravity to take you upwards and thus has to push you a little harder and thus you feel heavier). Now imagine that the elevator's cable snapped and the elevator is in a free fall. The elevator would start accelerating downwards at 9.8 m/sec2 (acceleration of any free falling object) and you would experience total weightlessness because the elevator and the person in it are falling at the same speed and the elevator's floor is no longer pushing the person (gravity does all the work).




Now comes the tricky part. If the astronauts and the shuttles are falling towards Earth, why don't they crash into the planet? How do they stay in the orbit?

This happens because shuttles and satellites are launched at a precise horizontal speed that helps them stay in the orbit. This speed is calculated such that the rate at which the shuttle falls towards the Earth is equal to the rate at which Earth curves away from the shuttle, thus keeping the shuttle at the same distance from the Earth always! You can read a detailed description of how satellites manage to stay in the orbit

One final thought. Why doesn't the satellite slow down from that initial launch speed? That is because these satellites are in vacuum and thus there is nothing to slow them down. It is the atmosphere on our planet that slows things down but there is no atmosphere in the outer space. In fact, it is to avoid Earth's atmosphere that satellites and space stations are located at least 200 miles from the surface. If not for the atmosphere and other obstacles like mountains, it is possible to launch satellites in an orbit just a few feet high!

Did the simple science for kids in this post make you a little smarter?
If you have any ideas / questions you want to learn about, please leave a note in the comments section. 
Would be glad to know if there are any inaccuracies in the article.

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