To Gravity or not to Gravity

Cmdr Nemo

Cmdr Nemo
drew said:
Earth has actual gravity caused by the mass of its composition. This is not the same thing at all. We're not dealing with gravity on a space station, only inertia. It would just 'feel' like gravity to us on board.

Stick with the interior of a more modest space station - easier to explain. Our frame of reference is external to the station and not rotating, so we see the station rotating. Peer inside and...

Whilst the person has a grip on the ball, both have inertia, but a centripetal force is acting on both the person and the ball from the floor of the station, pushing upwards towards the centre of rotation. The ball shares this force (let's keep things simple and assume the person is rigid throughout). If nothing happens both the ball and person describe a circle within the confines of the station due to its rotation and return to their starting positions after one rotation of the station. Crucially, both have a circular motion.

When the ball is 'dropped' no further force is acting on it, so it will continue in a straight line from our reference point. However, the person continues in a circular motion because the station floor is providing a centripetal force.

But the person is not in the same frame of reference as us, their frame of reference is rotating. So, from the persons perspective the straight line movement of the ball in our frame of reference appears to be a curve. They will perceive the ball falling in an arc until it hits the floor, at which point it will eventually stop moving due to friction.

Would look like this. https://space.nss.org/dropping-the-ball-in-a-rotating-space-settlement/

Cheers,

Drew.
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If it's the rotational spinning of the station that cause the ball to drop towards the floor and allow the person to stand in one spot with out floating about; AKA artificial gravity. Then both are moving in a circular motion in the same direction. Why wouldn't the ball according to the laws of physic which state an object in motion will continue to stay in motion until acted upon by another force or something to that affect; Stay in motion until hitting the floor, and because the floor is also in motion, cause the ball to bounce back to whence it came prior to it being dropped.

Perhaps I'm missing something but if one throws a ball upwards from their seat aboard an aircraft, regardless of how fast the craft is going the ball will come down again to the same location.that it was prior to it being tossed upward. It works the other way also, if one tosses a ball at the floor on an aircraft, it will bounce back to it's origin.
 

Phongsalt

Phongsalt
Cmdr Nemo LXXI said:
If it's the rotational spinning of the station that cause the ball to drop towards the floor and allow the person to stand in one spot with out floating about; AKA artificial gravity. Then both are moving in a circular motion in the same direction. Why wouldn't the ball according to the laws of physic which state an object in motion will continue to stay in motion until acted upon by another force or something to that affect; Stay in motion until hitting the floor, and because the floor is also in motion, cause the ball to bounce back to whence it came prior to it being dropped.

Perhaps I'm missing something but if one throws a ball upwards from their seat aboard an aircraft, regardless of how fast the craft is going the ball will come down again to the same location.that it was prior to it being tossed upward. It works the other way also, if one tosses a ball at the floor on an aircraft, it will bounce back to it's origin.
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Even if the plane was upside down?
I think AG is a bit of a misnomer.It seems to me the ideal state would be to generate a force sufficient to nullify or otherwise modify the effects of gravity.Some of this technology already exists in modern times,of course,
as does the baked potato, both fairly rudimentary yet eminently serviceable applications of the principles involved.
 
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Sapyx

Sapyx
Cmdr Nemo LXXI said:
If it's the rotational spinning of the station that cause the ball to drop towards the floor and allow the person to stand in one spot with out floating about; AKA artificial gravity. Then both are moving in a circular motion in the same direction. Why wouldn't the ball according to the laws of physic which state an object in motion will continue to stay in motion until acted upon by another force or something to that affect; Stay in motion until hitting the floor, and because the floor is also in motion, cause the ball to bounce back to whence it came prior to it being dropped.

Perhaps I'm missing something but if one throws a ball upwards from their seat aboard an aircraft, regardless of how fast the craft is going the ball will come down again to the same location.that it was prior to it being tossed upward. It works the other way also, if one tosses a ball at the floor on an aircraft, it will bounce back to it's origin.
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You are missing something: you might appear to be standing still while standing on the staiton floor, but you are actually moving, and you aren't moving in a straight line. You are constantly changing the vector of your velocity by moving around in circles, because you are attached (by friction) to a rotating station. The station is constantly pushing you around and around in a circle, while you "want" to obey Newton's laws and keep travelling in a straight line. The net effect is a force that sticks you to the station.

While you are holding the ball, you are forcing the ball to go around and around with the station as well. The moment you release it, it then becomes free to travel in a straight line (as Newton says it "wants" to do), like a stone released from a sling. And that straight line will take it outwards, towards the floor of the station, but because the floor of the station is rotating, then the ball will appear to move sideways, from the point of view of someone standing on the station floor.

Your airplane analogy: if you toss a ball up in the air, and the plane suddenly changes velocity (maybe the pilot hits the Boost button), then the ball will no longer drop down in a straight line - because the velocity of the plane has changed, but since the ball is not attached to the plane, it will keep travelling at the velocity the plane had when the ball was released.
 

Phongsalt

Phongsalt
Cmdr Nemo LXXI said:
If the craft is upside down, then the ceiling becomes the floor and the floor the ceiling. Upside down is a matter of perspective, there's no real difference it's a point of reference.
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Unfortunately that doesnt take into account the fact that the experiment is conducted in a 1g environment where gravity definitely has a point of reference.In a weightless environment up and down have less relevance than above and below.
 

varonica

varonica
Cmdr Nemo LXXI said:
If the station was for arguing purposes only the size of Earth. And both are rotating at or about a 1,000 miles an hour that the Earth is proposed rotating at. Why would the ball act any different on the station then the Earth. Going outside the box, Earth is nothing more than a space station if one were to get technical. Both rotate and revolve around stars. The difference is, any reference to up and down is backward from our norm.
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Even if the spinning space station was hollow and the size of the earth and you were standing on the inside the moment you jumped up from the floor, for instance, would put you in a state of almost zero gravity, arguably micro-gravity because there would be some small pull towards the surface you jumped from, but not enough to be noticeable. This is the difference between proper gravity and a simulated feeling of gravity from centipetal force. Centripetal force does not apply over distance like gravity, only while you are in contact with the object applying the force, that is the difference. Assuming that the inside is airless just for the point, once out of contact with the floor physics would dictate your behavior, which is that you would no longer move in a curved line dictated by the object applying centripetal force, but in a straight line until you struck something, probably the spinning surface, now moving at a speed relative to yourself.

With the example earlier of the ball, it's not the ball moving towards the surface we observe, it's two object moving in different direction intersecting, it just looks like a ball falling.

Of course in a small rotating station it wouldn't have a serious effect because your wold strike the surface fairly close to where you jumped up, but in a sphere the size of the earth a even a small jump would probably ensure the difference in relative motion to you and the surface applying centripetal force would be great enough to be fatal by the time you actually struck it. The calculations are just maths and physics and while I'm just not good enough to work it out in my head here that's all it is, any competent woiuld be able to tell you the answer in a few minutes.
 

Cmdr Nemo

Cmdr Nemo
Sapyx said:
You are missing something: you might appear to be standing still while standing on the staiton floor, but you are actually moving, and you aren't moving in a straight line. You are constantly changing the vector of your velocity by moving around in circles, because you are attached (by friction) to a rotating station. The station is constantly pushing you around and around in a circle, while you "want" to obey Newton's laws and keep travelling in a straight line. The net effect is a force that sticks you to the station.

While you are holding the ball, you are forcing the ball to go around and around with the station as well. The moment you release it, it then becomes free to travel in a straight line (as Newton says it "wants" to do), like a stone released from a sling. And that straight line will take it outwards, towards the floor of the station, but because the floor of the station is rotating, then the ball will appear to move sideways, from the point of view of someone standing on the station floor.

Your airplane analogy: if you toss a ball up in the air, and the plane suddenly changes velocity (maybe the pilot hits the Boost button), then the ball will no longer drop down in a straight line - because the velocity of the plane has changed, but since the ball is not attached to the plane, it will keep travelling at the velocity the plane had when the ball was released.
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Though the terminology is different, an aircraft flight is actually in an portion of an orbit. Yes it's duration is very short but an orbit never the less. My aircraft experiment doesn't take into effect the possible of speed changes during the experiment, the same as we have not taken into consideration the orbital speed of either a planet or a station during a ball drop either.


One isn't standing still on Earth either, just like a space station, we are actually moving and not in a straight line. And as you stated in reference to the station, the Earth is also pushing around and around in a circle. Spinning is spinning regardless if its in regards to a planet or a station. Though most planet spin or rotate, it's gravity come from a different source. A station also spins and in so doing causes an effect referred to as artificial gravity. If either were to stop rotating, only the station would loose its gravity.

If what you are saying is true and it might very well be. Then why if the Earth is spinning or rotating at a speed considerably faster that a station could ever do. Why does the ball dropped return to its origin but not on a station which is rotating exactly like the Earth only slower.

Both are spinning or rotating, both have a source of gravity the only difference is the size and the speed in which they both rotate. The physics should be the same. An object in motion regardless of how fast it's going will stay in motion.

Though a dropped ball on Earth appears to come straight back, because the Earth and the person who dropped it are both subjected to the same physics in regards to gravity and motion (Earth rotation). It would appear different from a vantage point other than the immediate area of the Earth.

I'd concur that from a vantage point other than the proximity of the space station it self. The descent and rise of a dropped ball would appear to be angular. But from the vantage point aboard the station just like it is on Earth, the ball would appear to go straight down hit the floor and then arise straight upwards again.
 

varonica

varonica
Cmdr Nemo LXXI said:
Both are spinning or rotating, both have a source of gravity the only difference is the size and the speed in which they both rotate. The physics should be the same.
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No they don't both have a source of gravity I will say it again, centripetal force is NOT gravity. Gravity is a force that acts over a distance, centripetal force acts on contact only! So if I throw a ball up on the earth it is pulled back toward the center of the earth by gravity and because the earth is so huge compared to ball size and height it appears to fall in a straight line, if I am in a rotating environment and throw a ball up there is no force pulling it back down, it simply won't fall down, it will continue moving in the direction I threw it until it encounters another object, the physics are enormously different.

Even so there is still a turning effect on the earth due to it's rotation, it's just that the earth is so large it's only noticable on a large scale, it's called the Coriolis effect and it's what causes cyclones and hurricanes but it does effect falling object, just not enough to notice.

So no, you are entirely wrong. First difference, you would need to throw the ball down because it simply wouldn't fall when you let it go, it would move at an angle until it struck the station wall well away from the point that appears directly below it. Second, after throwing it down it would bounce up and rise in a straight line determined by it's angle of striking and the speed of rotation of the object it struck, which wouldn't be back to the hand that threw it. Third, having missed the catch because the ball didn't come back to where you expected the ball wouldn't fall back to allow you to catch it, ti would continue in it's path across the empty space of the station until it struck the inner surface on the far side of the station. Well a bit around from that actually because the station surface is moving at the same time the ball is traveling across. But the ball will travel in a straight line across the station, only because you are also motion from your point of view it would appear to curve until it struck the surface.

The physics are massively different, with centripetal force we are looking at the physics of motion, with gravity we are looking at, well the physics of gravity!
 

babelfisch

babelfisch
Cmdr Nemo LXXI said:
I not sure exactly how the Earth provides gravity, something about it center core rotating one way while the surface is rotating differently. But a space station has no core rotating any differently than the rest of the ship.
If somehow the Earths rotation were to increase dramatically, we would be walking on the ceilings instead of the floor. And going outside would require an umbilical cord of sorts.
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The Earth's core creates the magnetic field, it doesn't have anything to do with gravity though.

Gravity is the result of uneven mass distribution, lots of mass = lots of gravity in unscientific terms. Earth rotation only has a minor affect on gravitational acceleration, something like 0-1% depending if you are at the equator or at one of the poles.
 

Arioch

Arioch
metatheurgist said:
Great vid. Only way it could've been better is if the entire thing was in an enclosed housing so the rotation wasn't apparent.
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It’s got me thinking that space legs pewpew could be a complete comedy of errors if any sort of grenade ever gets used in a Station o_O

(as an aside, Infinite Warfare had a space grenade that had micro-thrusters to direct it towards the point of aim, looked very cool as it jetted around)

An early episode of The Expanse had this great little moment where Thomas Jane poured some drink and the liquid curved into the glass due to Coriolis, and it wasn’t explained why it was bending like it did. I knew then I was going to like the series :)
 

M00ka

M00ka
Arioch said:
It’s got me thinking that space legs pewpew could be a complete comedy of errors if any sort of grenade ever gets used in a Station o_O

(as an aside, Infinite Warfare had a space grenade that had micro-thrusters to direct it towards the point of aim, looked very cool as it jetted around)

An early episode of The Expanse had this great little moment where Thomas Jane poured some drink and the liquid curved into the glass due to Coriolis, and it wasn’t explained why it was bending like it did. I knew then I was going to like the series :)
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Funny you should mention Infinite Warfare because one of the bit I didn't like about it was the 'no gravity' gunplay. Floating in space, firing projectile weapons and you didn't start to drift backwards? Please, at best it was an oversight, at worse just sloppy gameplay lol
 

Arioch

Arioch
M00ka said:
Funny you should mention Infinite Warfare because one of the bit I didn't like about it was the 'no gravity' gunplay. Floating in space, firing projectile weapons and you didn't start to drift backwards? Please, at best it was an oversight, at worse just sloppy gameplay lol
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I thought the suit jets compensated for gunfire, though I'd have to check other characters to see if their nozzles are thrusting (oo-er!) when they're shooting off (...I'm going to stop here).

A game that I thought did this really well was Shattered Horizon - you could essentially go FAoff and all artificial noise and jetpack compensation was switched off, so you could propel yourself around by gunfire and only hear your character breathing and the muffled sounds of your own gun.
 

Callabus

C
Thought I might be able to simplify the motion of the ball problem. The station is moving in a straight line at a constant velocity as are the ball and the man. This can best be described as an infinite number of straight line vectors. Because the station is curved, those straight line vectors will appear to be "pitching up" over any measurement of time to account for the curvature of the station. Because the station is curved it applies a force (centrifugal force) to the bottom of the man's feet and thus to the ball which the man is holding. This gives the appearance of 1 g of gravity.

If you want to understand the movement of the ball when it is released, all you have to do is draw a straight line from one side of the station to the other along the direction of travel. Thus, if the man was standing on a landing pad in the middle of the station, the line would be drawn from one wall of the station to the other wall through the ball parallel to the floor of the landing pad below the ball. If you follow that line through the ball, the ball will hit the floor of the station at the point where the line we drew intersects the station wall.

From the point of view of the man, the ball will appear to move in a slight curve behind him in a downward motion until it hits the floor. The reason for this is the man is travelling in a curve as the station moves. For an observer watching from just outside the mailslot and rolling his ship to keep himself level with the landing pad floor where the action is happening, the ball will move in a straight line across the statio until it hits the wall while the man will move in a curve along with the movement of the station.

As mentioned by several people, the affect of gravity is negligible because the station doesn't have enough gravity to apply any noticeable affect. At the moment the ball is released, it is no longer being acted upon by the centrifugal force applied by the station and thus will not accelerate to the ground at 32 feet per second squared.

Hope this helps :)
 
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Han_Zen

Han_Zen
I don't think there is any need for AG in ED. FD has it under control. Planets have their own gravity. Stations rotate at correct speeds and have varying experienced gravity, depending on distance to center axis. Ships don't have any gravity, so they are designed for mag. boots.
The only exception is the Imperial capital ship, that has a 1G ring for the comfort of their higer ranking officers and travelers.

It's all covered. Even with legs, we want run into situations where AG is needed.
 
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