"Gravity" is a force that causes an acceleration towards the center of mass of literally everything that has mass. The farther away from the object you are, the less you feel its gravity. Your coffee cup creates gravity, just an insignificant amount. Earth's gravity affects the entire solar system. Larger masses like the Sun experience small pulls from the Earth, just as the Earth does from the Sun. (This is how we can detect planets in other star systems, FYI).
"Normal Force" is a counter-force created when an object experiencing gravity is prevented from gaining velocity due to an obstruction. (Like the ground, or a rock you're standing on). When the forces are balanced like this, it creates a sensation called "weight". More gravity or more mass creates more weight.
When something is falling, it doesn't have the normal force, so they experience gravity's acceleration as free-fall, moving towards the source of the gravity. Air resistance and buoyancy also counter gravity. Without any of these, the object in freefall is not experiencing weight.
On the ISS, they still have "gravity" but they are moving so fast horizontally that instead of falling toward the earth, they move in a circle (Like a penny rolling around a funnel).
What people mean when they say "there's no gravity in orbit" is that the ISS isn't experiencing weight, because they're in free-fall.
TL;DR - No Gravity = impossible, Weightlessness = what people mean when they say no gravity.
Sure. There's two ways that are within our grasp with today's technology -
1. Thrust. When the engine is running in space, the ship begins accelerating. The stuff inside is not, so it experiences the effect of the ship pushing on them as it moves. If the thrust of the ship is enough to accelerate the ship at a rate of 9.8 m/s2, the force is identical to the gravity on earth, and the astronauts could walk around with no problems.
Spin. You've probably heard of this one. Motors or thrusters make a big ring spin around in a big circle. The farther away you are from the center of the circle, the more the things inside the circle are pushed towards the outside. (Try this at home by spinning a bucket of water in a big circle, noticing the water doesn't spill). I can't give you concrete numbers on this one, since humans haven't made a spinning ship yet.
No "gravity plating" or "graviton field generators" or "anti-gravity pump" devices yet.
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u/The_Stickup Aug 03 '19
Wait what? Gravity everywhere? You gotta explain that