Calculating Artificial Gravity for a Rotating Space Station

[Dale]

i think i have a misunderstanding about centripetal force and centrifugal force. I didn't think them in terms of upwards and downwards instead i thought them as pushing inwards and pushing outwards. So only thinking them in terms of pushing upwards and pushing downwards can help explain this? Correct?

The term "down" means "in the direction of the fictitious force". Since the fictitious force is "outwards" that means that "outwards" IS "down".

Edit: I see Nugatory answered essentially the same.

 

[ash64449]

The term "down" means "in the direction of the fictitious force". Since the fictitious force is "outwards" that means that "outwards" IS "down".

Edit: I see Nugatory answered essentially the same.

yes.. i was waiting for this! thank you DaleSpam for keeping patience.. i thought you would go out of patience by my questions...

 

[ash64449]

The term "down" means "in the direction of the fictitious force". Since the fictitious force is "outwards" that means that "outwards" IS "down".

Edit: I see Nugatory answered essentially the same.

Actually,i also figured it out when i was offline and went to say it to you.But i saw nugatory say the same!

 

[BugsBunny]

Ok Sorry but this all sounds totally looney-toons:

First, even if you could make a large enough space object where someone could stand up straight while it was turning underneath them, (anyone who ever spun a bicycle wheel by it's axle knows how hard it is to keep the wheel spinning in one plane.) Should there be a shift in MASS ie people moving around, especially with no friction this object would certainly become unstable in short order and simply disintegrate under all the extreme forces

Secondly, a merry-go-round on Earth already has gravity keeping it's occupants seated ... in space, objects while possibly moving in the same direction are not going to magically interact as if there were gravity ... the expectation would be in the case of a hollow circular tube that if you started the tub turning, any objects not tied down would not move with respect to the tube ... therefore any objects and or people would not be able to experience any of the artificial forces unless they were attached ... some might suggest magnetic boots could be used to achieve this

Third, even if you could build a ginormous spinning object big enough where the movement of people would be insignificant to its balance, there would be other issues of motion that a person would need to overcome ... moving in the direction of spin would probably be fine but any motion against the direction of spin would most likely be very disorienting ... being on a ship in heavy seas comes to mind

 

[Nugatory]

(anyone who ever spun a bicycle wheel by it's axle knows how hard it is to keep the wheel spinning in one plane.) Should there be a shift in MASS ie people moving around, especially with no friction this object would certainly become unstable in short order and simply disintegrate under all the extreme forces

What keeps the Earth spinning stably (stably enough) on its axis then?

The difficulty with holding a spinning bicycle wheel in one plane comes from precessional effects that are caused by the Earth's gravity acting on the wheel. In free fall, the spinning wheel would tend to remain in one plane and resist any effort to move it out of that plane.

ts while possibly moving in the same direction are not going to magically interact as if there were gravity ... the expectation would be in the case of a hollow circular tube that if you started the tub turning, any objects not tied down would not move with respect to the tube ... therefore any objects and or people would not be able to experience any of the artificial forces unless they were attached ... some might suggest magnetic boots could be used to achieve this

Any object that has any radial velocity at all will eventually move into contact with the wall. When it does, friction between object and the rotating wall will accelerate the object tangentially until it has the same velocity as the wall and the centripetal acceleration will hold the object there in the same way that gravity holds an object on the surface of the earth.

[quote[moving in the direction of spin would probably be fine but any motion against the direction of spin would most likely be very disorienting [/QUOTE]

Why? In fact, what experiment might you use to discover if you were moving with the spin instead of against it? Before you answer this question, you might want to consider whether you feel more disorientation moving to the west against the Earth's rotation, than you do when moving to the east with the Earth's rotation.

 

[BugsBunny]

Using the Earth as an example in your comments is like comparing infinity to a grain of sand ... in order to affect the spin of the Earth you would require a large cause (like the collision that created the moon) ... unless you are going to build another planet for your spaceship I would submit this is not a valid comparison. It is all about scale.

The MASS of said Space object would have to be big enough and or have enough means (fuel) to counterbalance any changes using technology perhaps similar to how the automotive industry uses weights in wheels and or crankshafts. You might be able to have movable counter weights and or use puff jets. Or somehow build a gyroscope that a human could survive in.

The effects of a spinning spacecraft where you are only tethered by your shoes I expect would not be trivial again this is all about scale ... there is little deviation in how the Earth moves and we are moving at the same speed due to gravity ... in a spinning spacecraft there is no gravity and the scale of this artificial force wouldn't be big enough I warrant for a human to NOT notice inner ear issues when moving in different directions.

If you take a bowl of water and spin the bowl there is a tendency for any solid in water to slowly migrate to the bowl due in most part to the friction of the viscosity of the fluid water... the viscosity of the "AIR" in the case of a space craft, is not as great as water (unless you now want to have an aquatic environment and grow gills) so again I propose that if a person is NOT tethered to the outside circumference surface, I highly doubt there would be any noticeable/usable gravitational effect artificial or otherwise. My prediction would be anything not tied down would become a projectile.

 

[Nugatory]

Uso again I propose that if a person is NOT tethered to the outside circumference surface, I highly doubt there would be any noticeable/usable gravitational effect artificial or otherwise. My prediction would be anything not tied down would become a projectile.

Don't guess, calculate it. Assume that the radius of the space station is, for simplicity, 100 meters. What speed must the outer rim move at to produce a centripetal acceleration of 1g at the rim? How much different will the speed and acceleration be at a distance of 98 meters from the center, where the head of a tall person standing on the rim would be located?

(The formula for centripetal acceleration is $a=\frac{v^2}{r}$)