I have come across multiple videos where an astronaut will let go of an object (just watched one where it was a bolt), and all of them tend to float upwards relative to the camera. Could it just be that earth is actually positioned “up” from the camera so gravity has an effect? or is it that when they let go of the object, they are subtly pushing it upwards? idk could somebody explain.
In: Physics
Weightlessness in the ISS or any other orbital bodies does not come from a lack of gravity, but a lack of gravitational force caused by being in free fall. A way to think about it is that the ISS is falling towards the Earth so fast that it continuously misses because it can’t change direction fast enough.
Imagine a person standing on a platform and throwing a ball horizontally. If they throw it gently, the ball will fall to the ground a short distance away. But if they throw it harder, the ball will travel farther before hitting the ground. Now, if they could throw the ball fast enough, it would fall towards the Earth but the Earth’s curvature would cause it to miss the surface and continue falling in a curved path, never actually hitting the ground. This is how satellites, including the ISS, maintain their orbit—they are essentially “falling” around the Earth but moving forward fast enough that they keep missing it.
The bolt and the astronaut are both in free fall, experiencing the same gravitational force. According to Einstein’s theory of General Relativity, in a free-falling reference frame, both the bolt and the astronaut feel as though they are in a state of weightlessness, as if no external forces are acting on them. This is because, locally, gravity can be thought of as being “cancelled out” by the free-fall motion.
From the perspective of the bolt and the astronaut, they are in what is called an inertial frame in the context of General Relativity. In this frame, they do not feel any force acting on them because they are both accelerating at the same rate due to gravity. This is why they float relative to each other. There are no additional forces acting on them from their perspective because they are both in free fall together, experiencing the same acceleration due to gravity. This absence of felt force is why astronauts inside the ISS experience weightlessness.
I’ll wrap this up as other answers already do a great job of explaining why things tend to float up, but hopefully this expands on the mechanics of free fall and gravity.
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