Image a world that superficially appears to have Earth-like gravity. However, the moment you do not in any way touch the ground or something else that is touching the ground, there is no gravity for you. E.g.:

  • You jump, you're floating.
  • You run (definition= "to go quickly by moving the legs more rapidly than at a walk and in such a manner that for an instant in each step all or both feet are off the ground"), you float.
  • You touch a wall or somebody standing/sitting/whatever and then jump, it will be like a jump on Earth.

This is true for everything (animals, stones, houses, water, etc.) except atmosphere (or no one would be able to breathe).

To go back to the ground, you'll have to touch something that is already touching the ground. (And depending on what hight your are, you could easily crash.)

I imagine that transportation could get easier. But behaviour like throwing would not be recommended.

How does this change every day life? (Imagine a 21st century development)
Would keeping the momentum make life more complicated? (E.g. when jumping up, you would keep your momentum - like in vacuum? - and float up)

I was thinking about movement in space with my question about the momentum: E.g. thrusters of an Earth space probe fire in direction A, they move the space probe in opposite direction B with low friction. Thus, a person jumping is like a space probe whose thrusters fired.

  • $\begingroup$ "Keeping momentum" would be free energy and cause a LOT of issues. i'm pretty sure you do not want that. "keeping momentum, no friction" would cause even more. $\endgroup$ – Mołot Aug 21 '16 at 11:34
  • $\begingroup$ If you touch the air, and the air touches the ground, you have gravity. So you have always gravity. If air doesn't "conduct" gravity, then what is the line? Does pure oxygen conduct gravity? Does pure Co2? What about other Gases? $\endgroup$ – Polygnome Aug 21 '16 at 11:39
  • $\begingroup$ In order to keep the momentum you would have to eliminate friction as well. The momemt you jump, you will otherwise start to slow down. Having no fraction however means that ordinary brakes don't work, either. Have you thought about how that would work out? $\endgroup$ – Polygnome Aug 21 '16 at 11:39
  • $\begingroup$ What happens if I throw a table? Does it also float? Sorry about all these questions, but I'm having a hard time picturing how your world might actually work. The idea is interesting, but it seems to be difficult to work out consistent details... $\endgroup$ – Polygnome Aug 21 '16 at 11:40
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    $\begingroup$ @Polygnome But we know that keeping momentum doesn't make sense. Sometimes being too literal can be a trap (I've fallen into it too many times myself). $\endgroup$ – a4android Aug 21 '16 at 12:17

I am assuming one additional rule: dust or very small particles would be affected by the gravity just like the air. This will avoid the particularly grim scenario that Mołot offers.

I would assume this world would have creatures that fly around. And there is no reason to not have one. You don't even need to be light to fly. Also the wings would be different, they would be more like fins. Probably most life will never touch to the ground. In fact touching the ground will be like having a curse: the curse of gravity. Something that you would use to scare the children.

  • $\begingroup$ Your additional rule is most helpful in keeping my imagined variations between gravity and still have life on that planet. Thanks! $\endgroup$ – Grüg Aug 24 '16 at 13:41

Keeping momentum won't work

Either your world is frictionless, and that's really hard to imagine and simply couldn't work anyway near our world does, or you break energy conservation. If the latter, rock floating in atmosphere (think close orbit) would constantly produce friction heat. It will make atmosphere hotter and hotter, without real limit. Oceans would boil out, atmosphere would turn to plasma etc.

No gravity without touching

So back to the main question. World like this could not develop. Sand raised by wind would never drop back to the ground. Raindrops wouldn't fall. Rocks and splinter created by lightning hitting ground? In the air. Forever. Volcanic ash? Same here.

You would have a LOT of abrasives up in the air. Erosion on unimaginable scale. Your world would be pretty flat, and air would be unsuitable for breathing, unless your creatures would have really, really good air filters. Or (as I believe) life would stay at single-cell level or only slightly higher. Or underwater, where things are pretty normal.

  • $\begingroup$ Why would air/atmosphere not be able to cool down? (I'm no physicist, but I'm thinking about Venus with an atmosphere that keeps it hot and sun rays that make it even hotter - and at the same time Venus' temperature doesn't rise limitless. So, there seems to be a way to "lose" temperature?) $\endgroup$ – Grüg Aug 21 '16 at 17:50
  • $\begingroup$ There are ways to lose temperature, but are limited. With items not falling and not slowing down, energy source is limitless. With each new item equilibrium will be at hotter temperature, and at some point it will have to get too hot. $\endgroup$ – Mołot Aug 21 '16 at 18:34

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