Because everything in the universe has a definite volume. everything with a volume must have a mass. mass is the amount of "stuff" in a given volume. so if you were to weigh even the smallest particle it would have a weight most likely measured in amu ( Atomic Mass unit). everything has a weight because everything has gravity. whether by centripital force, atmospheric pressure, or any type of atomic bond.
No.
they're almost weightless, so nothing
rawr
a hole
Nothing. In space, things will be weightless.
air. his breath.
Not really, but on other parts you experience weightlessness
Yes, but they do have the same mass. Weight is based off the effect of gravity pulling something down, because there is no gravity in space astronauts are weightless.
because both the astronaut and the satellite is attracted towards the center of the earth
No. It is light -- not heavy, but it is not weightless.
A shadow is something that is weightless but can be seen.
Yes, but not advisable unless the plane is designed for aerobatic flying. There is nothing illegal about rapidly descending which would be required for a weightless condition. The rate of descent is at the pilots descretion. He should not overload the airplane.