I don’t know why I’m so obsessed with this. I know that rotational gravity is real. I’ve been on a tilt-a-whirl, I just don’t fully understand WHY it works.
Here is a scenario to illustrate what I mean: I am an astronaut inside a “hollow donut” type ship like in 2001. There is no air, we are in space. No relative gravity whatsoever from anything else. I am inside the ship, it is not moving or spinning and I am not close to the hull or anything.
From what I understand if the ship begins to “spin” to induce the artificial gravity effect, I will be affected by it and pushed out toward the outer wall or hull.
Why? What is ACTING on me. I know it might sound like a weird question. I love science and am convinced by it 100% I just feel like I don’t get what exactly is going on.
In: Physics
Let’s say you’re in this contraption and you jump. From an outsiders perspective, when you jump, the ship keeps moving below your feet and eventually “catches you”, giving the impression that you fell. In reality, the ship simply moved into you.
In your example, you would not start to drift toward the wall. In your/the inertial frame, there is no force on you, and therefore you do not experience acceleration. In the rotating frame of the ship, the centrifugal force on you would exactly counter the Coriolis force on you, since in that frame of reference you are the one moving around the ship.
In practice, rotational gravity works by causing everything to rotate with the ship. If the ship is filled with vaccum, and you are not touching the walls or anything, the ships rotation does not affect you (until you drift into a now rapidly moving wall)
Nothing is acting on you, at first. If the ship begins to spin, but you aren’t touching the walls, it will spin without you. This will look very upsetting to anyone standing on the inner walls, and you’ll see them whirling around you. Eventually, the ships’s air will start to spin with the ship, and the air will eventually push you into the wall/floor. This might hurt, depending on how fast the spin is.
“a Moving object will continue moving in a straight line unless something makes it change”- A very simplified version of Newton’s first law of motion, but good enough to explain.
When the Spaceship spins, you move with it. Your body wants to continue in a straight line all the time, but the floor of the ship gets in the way, constantly changing your motion from a straight line to a curved one. It’s this change that causes an effect that feels like gravity, causing you to be pressed against the floor as the direction your body wants to go constantly fights with the direction the ship is forcing it to go.
If you’re floating in the ship with no air, then no, the rotation won’t affect you, you’d just float there as it spins. The tilt-a-whirl only does that because you’re attached to it – if you could hover 6 inches off the ground, it would just spin underneath you as well.
> I just don’t fully understand WHY it works.
Objects in motion tend to remain in motion unless acted upon by an unbalanced force. This means that if you are drifting through space you are going to keep going that direction unless something makes you move a different direction. When that happens you are going to feel a force.
So to make you spin around in a circle you are being continually made to change your direction. On one side of the circle you are going one direction, and on the other side you have been accelerated such that you are going the completely opposite direction. The force you interpret as “pulling you to the ground” is actually the force opposing your inclination to just fly off in a straight line.
> From what I understand if the ship begins to “spin” to induce the artificial gravity effect, I will be affected by it and pushed out toward the outer wall or hull.
No, you will not. You would need to be spinning with the wall or hull in order to be inclined to fly off in a straight line, and have the wall/hull stop you creating the simulated gravity. Without moving you are just going to be sitting next to a spinning torus. If you grabbed onto the torus you would start needing to resist being flung off, right? That is the artificial gravity.
If you aren’t touching the rotating hull, you won’t start rotating with it (barring eventual air resistance effects), and will not experience the artificial gravity, no. It works because moving objects travel in straight lines on their own. Once you’re rotating with it, your mass wants to continue straight, which would send you through the outer wall of the station. This means you’re constantly crashing into the wall, which pushes back because it is solid, and the result is an apparent gravitational force holding you down against it.
There isn’t any real gravity created here. It only seems that way because curved paths require an inward force to maintain them, and collision with the wall/floor makes sure that happens.
You aren’t being pushed towards the outer wall. You are being thrown off into space, but there just happens to be something there to impede you.
Think about it this way: If you pick up a baseball and spin your arm in a circle, what direction does the ball go when it is released? It doesn’t continue to go in a circle, right? It goes flying off in whatever direction it was travelling when you released it. An object in motion stays in motion until something else acts on it. The ball is constantly being accelerated off in some direction, but as long as you hold onto the ball it can’t go flying away.
This is what is happening in the space ship. The person has been accelerated, but they are constrained by the hull of the ship. If the hull magically disappeared, they would go flying off into space in a straight line direction. But the hull is there, so it “catches” them and redirects their motion.
Just like the way your hand constantly “catches” the ball until you are ready to release it, the hull constantly “catches” you to prevent you from being thrown away from the ship.
The “rotating ship” will not affect you unless you are moving along with the rotating part of the ship. If you are not moving you will see no apparent gravity. If you are moving faster or slower, you will see more or less apparent gravity, respectively.
If you start out free floating, an easy way to get up to speed is to attach yourself to the rotating part. Once you get some speed, you can stand on the rotating surface, and the friction will eventually be enough on it’s own to get you up to the same speed
I say “apparent” gravity because it’s not real gravity. Gravity doesn’t act that way. Remember the scene in 2001 where they are jogging around the inside of the room? If they jog in the same direction as rotation, they’ll feel more weight than if they jogged in the other direction. That could be as problem for sprinters
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