Outside the earth’s gravitational field, astronauts experience “weightlessness”. Their mass has not changed, but with no gravity to act upon this mass, they have no weight. When working outside a spacecraft, astronauts are tethered to prevent them from floating away into space. Inside the spacecraft, liquids have to be sucked through straws. Liquid would not be held in an ordinary cup by gravity, as it is on Earth, but would spray all over the interior. One of the reasons that astronauts are spending longer and longer periods in space is so that scientists can study the effects of weightlessness on their bodies, so that future space flights can last for months or even years.
On Earth, we are pulled down towards the Earth at 9.81 meters per second squared, meaning that if we weren’t pressed up against the ground, our speed would increase by 9.81 meters per second every second! This is known as free fall. This is something that can be experienced during the initial phase of a skydive, during turbulence in an airplane, or while going down a steep part on a roller coaster. It is often accompanied by a weird queasy feeling in the stomach.
By taking a water bottle and drilling some holes in it, we can see why the astronauts are weightless. Both the bottle and the water are being subjected to Earth’s gravity. When the bottle is held still, the water falls out through the holes because gravity is pulling it down. Then, when the bottle is released, they are both pulled down at the same rate. With no difference in acceleration between them, the water floats happily inside the bottle and doesn’t go out the holes at all.
This is actually what is happening to those astronauts. When something is in orbit around the Earth, it is being pulled down by the force of gravity. For the ISS, this is about 9 meters per second squared! If the ISS wasn’t moving above the Earth, it would fall to the surface in less than an hour. However, Astronaut Scott Kelly was just on board for a year and didn’t plummet to his fiery doom. This is because the ISS is not staying still. Not even a little bit.
The ISS goes at about 17,000mph, which is over 10 times the velocity of a speeding bullet. This is entirely necessary, because as gravity yanks the ISS down towards the surface, the space station has moved far enough to miss the surface. This balance is very precarious. If the ISS were going faster, it would instead get farther away from the Earth each time and escape into space. If it were going slower, it would constantly get closer to the Earth.
Picture Credit : Google