For objects in orbit of Earth, does the force of gravity vary depending on where the object is in its orbit? Would astronauts be slightly taller at one point of an orbit than at another point (assuming they’re ‘standing’ with feet towards Earth)?
In: Physics
Theoretically yes. With something much heavier than the earth you can calculate the height difference. There’s even a thing called spaghettification which is exactly what it sounds like. Being pulled long like a spaghetti by really strong gravity.
In the earths orbit the difference in height is not that great because the acceleration is proportional to 1/distance squared. So it gets really small really quickly if you start at 10.
Yes. Mass is imperfectly distributed. The earth bulges around the equator as it spins, the earth’s tilt varies, and other bodies around the earth are also dynamic, like the moon, or asteroids.
The force of gravity does vary at different points in the orbit. However, things in orbit are in free fall, falling together. Nothing is pulling or pushing your feet differently than your head, and this is true no matter where you are in the orbit.
Astronauts do find that their spine lengthens somewhat during free fall, so they are slightly taller than they are on the ground. But the height doesn’t go up and down at different points in orbit.
Yes, but not enough to care about for most objects
When an object is in orbit its not experiencing a net acceleration, that means that the pull of gravity is balanced out by the centrifugal force from its fast orbit.
But for non-point sources there is both a gravity gradient and a centrifugal force gradient in opposite directions. For the center of mass of the object the orbital velocity is perfect so the middle doesn’t get any weird forces. The planetside part of the object experiences slightly stronger gravity and is moving a bit slow for its orbit height so the centrifugal force doesn’t cancel it all out. The farther side is moving a bit fast and experiences less gravity so its being pushed away from the planet.
The end result is that there is a stretching force on real things that are in orbit, but its really small for things that aren’t hundreds of meters tall and isn’t strong enough to overcome well connected materials like in our body or metals. The stretching force is mostly a problem for asteroids that happen to be big piles of rock with nothing holding them together but their own gravity, if they get inside the Roche Limit(the line where it starts to matter) then the rocks on the outside and inside will start moving away from the middle and the whole thing falls apart into a loose blob of rocks instead of a hearty asteroid.
It doesn’t matter for practical purposes in orbit. But variations in local gravity are a thing and they are important to geologists and geophysicists. Measuring local, gravity can give you an idea about the structure of the crust below.
Latest Answers