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By_AspenRH t1_j6ts6iz wrote

Physics - would a ship have to be under constant thrust to have gravity? As there's no friction in space surely a lack of thrust would just mean the momentum would carry on?

Biology - If humans were exposed to less gravity - lets say on mars and grew up in this condition, what would happen to their bones? How would they feel on a planet of different gravity? Would their skeleton be able to grow accustom to it?

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AutisticFrenchGuy t1_j6tu1pg wrote

For the thrust part : yes, the artificial gravity created in the ship would just be the floor pushing you towards the ship's up. This is why the designs of spaceships with artificial gravity all have a rotating part usually around the axis of the ship. There is a permanent centrifugal acceleration (as long as the rotation exists) in the part that is moving. The artificial gravity would be in this moving part there are some specificities to this type of artificial gravity because of the inertia and momentum in circular motion. There is a great Tom Scott video on this subject I'll try to find it.

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TheSpaceBird t1_j6vu1le wrote

For your biology question re gravity. There are actually a lot of interesting studies on this using the International Space Station. Sometimes when astronauts return to Earth they cannot stand at all due to their muscles degrading as they become disused. For bones I would think that without as much gravity they would be able to grow longer resulting in taller people. Indeed, when astronauts return from the ISS they are taller than when they left as their spine is less compressed.

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somewhat_random t1_j6w4f2a wrote

Both these possibilities are well explored in the Expanse series of books (and TV shows).

If a ship is always under thrust, people inside will experience the equivalent of gravity. Humans need gravity (as evidenced by issues of returning astronauts).

If you had a VERY efficient fuel source, you could remain under thrust throughout your journey except at the mid point where the ship must flip (i.e. accelerate at 1.0 g for half the trip and then decelerate for the second half and so have almost constant gravity). This uses a LOT of fuel though so is not practical with any known propulsion system.

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