OK, just so I understand this part: My butt and Earth are hurtling through space at the same rate of speed. I understand that, if not for gravity, my butt would drift away from Earth and take the rest of me with it. And, from what I understand so far from this thread, the reason my butt and Earth are attracted to each other is because they both have mass. My desk also has mass, but the reason the desk doesn’t pull my butt across the room toward it is because the Earth’s mass is far too great, and exerts more pull; the only way my butt hits the desk is if the desk is between Earth and butt (i.e., the act of sitting down).
So, why do astronauts have to be tethered to the space shuttle in space? Obviously, the shuttle has far greater mass than the astronaut – why wouldn’t it attract the astronaut’s mass to it? How much mass does something have to have to create a gravitational field?
Any mass at all creates a gravitaional field. But Gravity is just one force. If I push myself away from the space shuttle, I can easily overcome the effect of gravity and just start floating off into space (or falling to the earth). Gravity is a pretty weak force, compared to electromagnetism for example. I gave the equation in my first post above, so you can put in numbers and calculate it if you want. Just look up a value for “G” in wikipedia or another source.
Not a lot, but It takes all of the Earth’s mass too keep your butt on your seat and it’s not that much work to raise it up. The gravitational pull of the shuttle on an astronaut is tiny, nothing like strong enough to keep them stuck together.
G ~ 6.7 * 10[sup]-11[/sup]
Shuttle ~ 50,000 Kg (I have no idea but gotta be something like)
Hell, I’ll do the honours: if you’re 5 m away from the space shuttle, and you and your spacesuit weigh 100 kg, then the force between you and the space shuttle due to gravity is about 3 x 10[sup]-5[/sup] Newtons. This is about the same amount of force that the Earth exerts on a mosquito here on the surface. The main thing to remember is that the Earth has 50,000,000,000,000,000,000 times more mass than the space shuttle.
As an aside: the astronauts would come back pretty close to the Shuttle if they started drifting away, since at that point they’d just be on a slightly different orbits around the Earth. Assuming that the “drift” isn’t too large, these orbits will have the pretty near the same periodicity, and so they’ll intersect again after one trip around the Earth. Of course, this gives the astronaut nothing to do for 90 minutes but twiddle his thumbs, so perhaps this isn’t the best idea.
Pretty good until that last step. One kilogram weighs about ten Newtons on earth, so an object that weighed 10[sup]-6[/sup] Newtons would have a mass of 10[sup]-7[/sup] kilograms, or about one-tenth of a milligram.