artificial gravity

[Armoured]

The 'jump' would be limited by the force exerted upon the diver in the water, to remain at the bottom of the bucket
The diver would not be able, to reach escape velocity

Imagine the gravitational PULL upon the astronaut
that decides to climb toward the axis of a spinning ferris-wheel (type) space station
He would not be able to float toward it, but would, if he let go of the ladder, FALL
toward the outside edge (floor) if the station (centrifugal force)

"but centripetal force only affects objects at in contact with the spinning inner surface"

I would have said: that it effects EVERYTHING between the axis and, the outside edge (?) *

Yes it does take some thinking OUTSIDE THE BOX (imagination)
but, I am sure you will get so far

* The faster the spin and the greater the circumference
the greater the force imposed upon mass, situated
between the axis and the outside edge of the circumference

But in centripetal gravity environment, as I understand it, any jump sufficient to get one off the floor would, by necessity, be escape velocity for that context, wouldn't it?

 

[essentialsaltes]

The conversation has gotten a little muddled, and it's definitely hard to explain in words. So, for once, it is internet video to the rescue:

Note that when the 'camera' is fixed and floating in space (so that you can see the space ship rotating) the balls all travel in a straight line. This is what we expect from Newton's laws. There's no real gravity there to act on the ball, so it travels with constant speed and direction until it hits the floor again.

When the camera is fixed to the space station, then the ball's trajectory looks like various curves. Since the spacestation is rotating, the camera is in an accelerating (or noninertial) frame of reference, and it looks like the ball is affected by a 'gravity-like' force. This is essentially the Coriolis Effect.

 

[Armoured]

The conversation has gotten a little muddled, and it's definitely hard to explain in words. So, for once, it is internet video to the rescue:

Note that when the 'camera' is fixed and floating in space (so that you can see the space ship rotating) the balls all travel in a straight line. This is what we expect from Newton's laws. There's no real gravity there to act on the ball, so it travels with constant speed and direction until it hits the floor again.

When the camera is fixed to the space station, then the ball's trajectory looks like various curves. Since the spacestation is rotating, the camera is in an accelerating (or noninertial) frame of reference, and it looks like the ball is affected by a 'gravity-like' force. This is essentially the Coriolis Effect.

Cool! Thanks for posting.

Now, back to my point about entering from the axis, and then descending towards the floor. You'd essentially appear to "hover" above the floor if you never made contact with it, right? Obviously the floor would move beneath you, but unless you touch the floor, to an observer standing on the floor, you would appear to defy the "downward pull" of the artificial gravity, right?

 

[davedajobauk]

If your size and weight (mass) were negligible (an inflated balloon)
you would still FALL to the outside (albeit slowly)

The gravity you would experience, would depend upon the speed of rotation
For the purpose of this conversation, you are moving as one with the station
and, probably, walking on the (inside) of the outermost wall
and any 'wall' parallel to it (?)
Floating 20 - 30 feet, in 1g ~from the axis, of the station
would cause you serious harm
as would falling from a second (or third) storey window, here on earth

 

[Armoured]

If your size and weight (mass) were negligible (an inflated balloon)
you would still FALL to the outside (albeit slowly)

The gravity you would experience, would depend upon the speed of rotation
For the purpose of this conversation, you are moving as one with the station
and, probably, walking on the (inside) of the outermost wall
and any 'wall' parallel to it (?)
Floating 20 - 30 feet, in 1g ~from the axis, of the station
would cause you serious harm
as would falling from a second storey window, here on earth

Why would you fall towards the "floor" from the axis if you'd never been in contact with the "floor"? For the sake of argument, let's assume a vacuum inside.

 

[essentialsaltes]

Cool! Thanks for posting.

Now, back to my point about entering from the axis, and then descending towards the floor. You'd essentially appear to "hover" above the floor if you never made contact with it, right? Obviously the floor would move beneath you, but unless you touch the floor, to an observer standing on the floor, you would appear to defy the "downward pull" of the artificial gravity, right?

If you're at the center, and used a puff of jet pack to 'descend' and an equal puff to stop your motion, then yes, you'd hover above the floor as it rotated past you.

 

[davedajobauk]

Unless you were in a suit environment, you couldn't be in a vacuum (?)

You need to envision, that force from the axis, PULLING in an outward direction (toward the circumference)

 

[essentialsaltes]

that is, if we make all the usual simplifying assumptions. Air resistance would be complicated, and would eventually tug you enough that you'd wind up touching the floor

 

[davedajobauk]

If you're at the center, and used a puff of jet pack to 'descend' and an equal puff to stop your motion, then yes, you'd hover above the floor as it rotated past you.

This is illogical.....

If you are at the axis (in a vacuum) and wanted to move to the circumference
you could kick off of the axis and FLOAT to the outside and ~landing at the same speed as at take-off
Provided the ferris wheel was not spinning

If you are in air, and the ferris wheel is spinning slowly, you would gravitate toward the circumference
As the ferris wheel speeds up, the gravitational-pull to the outside circumference also increases
~a parachute might slow your descent, but you would surely descend

 

[whois]

There is 'something wrong with this 'thinking'

It wouldn't be, like you are on 'a moving pavement'
You are (when standing still) moving in conjunction with the floor (?) **
and so, will continue moving with the floor while you are in the vertical jump (?)

??

** I can give you another example of this

You are travelling on a train (at High Speed)

You jump up vertically, and will LAND upon the same spot ??
iow: you will NOT lose the velocity you SHARE with the train
while you are in the air

the train analogy doesn't apply because you are assuming a linear (straight) track.
plus, you are also assuming gravity, which doesn't exist on the station.
you do not fall back down on the station.
the floor rotates up to intercept you.

 

[whois]

This is illogical.....

yes, but quite possibly true.
remember, gravity does not exist on the station.
any time you are "decoupled" from the station, you are at the mercy of your own motions.
it certainly seems that if you jump up at the right speed and angle, you could become "stuck" in mid air.

 

[essentialsaltes]

You need to envision, that force from the axis, PULLING in an outward direction (toward the circumference)

What force is that?

Maybe this helps. The only force is one from the floor of the spacestation onto the bottom of your feet (if you're standing on it). And it pushes up. You want to move in a straight line (as per Newton's laws), so the only way to get you to move in a circle is to exert a force, and that's what the floor does, pushing you up toward the center of the station at every moment, constantly. Or with the pail of water. If the pail wasn't there, the water would fly free. The bottom of the pail pushes the water in toward the center of rotation.

When the contact between your feet and the floor is broken, as when you jump, the floor can no longer exert a force on you, because it's not touching you in any way. So that constant upward force is removed.

But your frame of reference is very used to that constant upward force. You think you're just standing there at rest, when in fact you are under constant force and acceleration. So from that frame of reference, when the constant upward force is removed, it seems to you like suddenly there's a downward force. But in fact there is no force pushing you to the outside. You're just travelling in a straight line, like the balls in the video.

 

[essentialsaltes]

As the ferris wheel speeds up, the gravitational-pull to the outside...

There is no gravitational pull to the outside. Gravity comes from masses acting on each other. Whether the station is rotating or not, its mass is the same, so whatever tiny gravity it exerts on you is the same, whether it rotates or not.

 

[Loudmouth]

I appreciate how momentum is maintained, e.g. why flying insects don't get squished against the back window of the car, but as I understand it, jumping inside the station, or even decsending from the axis of rotation, would negate the momentum.

It wouldn't negate it. If you were moving in an elevator from the hub to the outer ring of the space station you would be pushed to one of the walls of the elevator as you are accelerated in the direction of rotation for the space station. The same for moving in an elevator from the outer ring to the hub.

As for jumping, you still carry the momentum in the direction of the rotation which is at a right angle to the radius of the circle, so you will continue to fly in that direction until you hit the surface again.

 

[Armoured]

If you're at the center, and used a puff of jet pack to 'descend' and an equal puff to stop your motion, then yes, you'd hover above the floor as it rotated past you.

That's what I thought. Thanks for putting it better than I managed.

 

[Oafman]

Why would you fall towards the "floor" from the axis if you'd never been in contact with the "floor"? For the sake of argument, let's assume a vacuum inside.

To add to what ES wrote, this is an explanation which helps me to understand it, and in general to understand why centrifugal force only exists in our heads:

Imagine you're driving a left-hand drive car, quite quickly, around a long sweeping bend to the right. You feel like there is a force acting on you, pushing you against the driver's door. We call it centrifugal force, but there is no force pushing you outwards, against the door.

Instead, what is happening is that your body wants to keep going in a straight line, but the car is turning. So your body keeps going straight ahead, following its momentum. And because the car is turning, it doesn't take long before your paths intercept, and the car door starts to push against your shoulder, diverting your straight line momentum as it turns. As you continue around the bend, the car door is constantly pushing you, adjusting your straight line momentum.

So there's never a force pushing you outwards, against the car door. The only force acting on you is the force of the car door constantly pushing against your shoulder and changing your direction of momentum.

The same happens in the space station. It can be thought of in the same way as being in a car going around a never-ending and consistent bend. An astronaut always has straight line momentum, and the floor of the station ring is constantly correcting the direction of their straight line momentum.

If you jump, you still have your momentum, so you'll appear to 'fall' diagonally back to the floor. Like in the car, if you push yourself off the door and into the centre of your seat, as long as you're turning the car you would still feel like there is a force pushing you back towards the door.

This also explains what you don't land on the same spot from which you jumped. Because, for the time that you're not in contact with the floor, there is nothing correcting your straight line momentum. So for a second or two, your direction of travel is different from that of the floor beneath you, as it turns around the centre of rotation, while you don't. Your different directions of travel explain why, when your feet meet the floor again, they meet it in a slightly different place.

This is reasonably clear in my mind, but having just read that back, is not particularly clear in the words I've written. I guess this is why physicists use maths rather than words to describe things....

 

[Loudmouth]

This is illogical.....

If you are at the axis (in a vacuum) and wanted to move to the circumference
you could kick off of the axis and FLOAT to the outside and ~landing at the same speed as at take-off
Provided the ferris wheel was not spinning

If you are in air, and the ferris wheel is spinning slowly, you would gravitate toward the circumference
As the ferris wheel speeds up, the gravitational-pull to the outside circumference also increases
~a parachute might slow your descent, but you would surely descend

If the ring were in vacuum, what would be accelerating you in the direction of the spin?

 

[Oafman]

Incidentally, a rotating ring isn't the only option for generating artificial 'gravity'.

All you need is a spinning spacecraft, and a place for people to live which is as far as possible from the centre of mass, around which the ship is spinning.

If a spacecraft extends something heavy on a tether, then the further it extends, the further the centre of mass moves away from the main part of the spacecraft. So when it rotates around this point, you have artificial gravity. This is far simpler, in terms of the engineering challenge, than attempting to build a big pressurised ring in space, so is being actively considered for manned Mars missions.

 

[Loudmouth]

Incidentally, a rotating ring isn't the only option for generating artificial 'gravity'.

All you need is a spinning spacecraft, and a place for people to live which is as far as possible from the centre of mass, around which the ship is spinning.

If a spacecraft extends something heavy on a tether, then the further it extends, the further the centre of mass moves away from the main part of the spacecraft. So when it rotates around this point, you have artificial gravity. This is far simpler, in terms of the engineering challenge, than attempting to build a big pressurised ring in space, so is being actively considered for manned Mars missions.

That system would work well for a manned spaceflight, but rather poorly for a structure that would house millions of people.

 

[davedajobauk]

yes, but quite possibly true.
remember, gravity does not exist on the station.
any time you are "decoupled" from the station, you are at the mercy of your own motions.
it certainly seems that if you jump up at the right speed and angle, you could become "stuck" in mid air.

If you are INSIDE the 'spinning station (described above as a ferris wheel)
your mass is being thrown to the wall of the circumference 'gravity' that is created by 'centrifugal force'
that wall contains you, like the base of the bucket contains the water within the bucket

What force is that?

Maybe this helps. The only force is one from the floor of the spacestation onto the bottom of your feet (if you're standing on it). And it pushes up. You want to move in a straight line (as per Newton's laws), so the only way to get you to move in a circle is to exert a force, and that's what the floor does, pushing you up toward the center of the station at every moment, constantly. Or with the pail of water. If the pail wasn't there, the water would fly free. The bottom of the pail pushes the water in toward the center of rotation.

When the contact between your feet and the floor is broken, as when you jump, the floor can no longer exert a force on you, because it's not touching you in any way. So that constant upward force is removed.

But your frame of reference is very used to that constant upward force. You think you're just standing there at rest, when in fact you are under constant force and acceleration. So from that frame of reference, when the constant upward force is removed, it seems to you like suddenly there's a downward force. But in fact there is no force pushing you to the outside. You're just travelling in a straight line, like the balls in the video.

To add to what ES wrote, this is an explanation which helps me to understand it, and in general to understand why centrifugal force only exists in our heads:

Imagine you're driving a left-hand drive car, quite quickly, around a long sweeping bend to the right. You feel like there is a force acting on you, pushing you against the driver's door. We call it centrifugal force, but there is no force pushing you outwards, against the door.

Instead, what is happening is that your body wants to keep going in a straight line, but the car is turning. So your body keeps going straight ahead, following its momentum. And because the car is turning, it doesn't take long before your paths intercept, and the car door starts to push against your shoulder, diverting your straight line momentum as it turns. As you continue around the bend, the car door is constantly pushing you, adjusting your straight line momentum.

So there's never a force pushing you outwards, against the car door. The only force acting on you is the force of the car door constantly pushing against your shoulder and changing your direction of momentum.

The same happens in the space station. It can be thought of in the same way as being in a car going around a never-ending and consistent bend. An astronaut always has straight line momentum, and the floor of the station ring is constantly correcting the direction of their straight line momentum.

If you jump, you still have your momentum, so you'll appear to 'fall' diagonally back to the floor. Like in the car, if you push yourself off the door and into the centre of your seat, as long as you're turning the car you would still feel like there is a force pushing you back towards the door.

This also explains what you don't land on the same spot from which you jumped. Because, for the time that you're not in contact with the floor, there is nothing correcting your straight line momentum. So for a second or two, your direction of travel is different from that of the floor beneath you, as it turns around the centre of rotation, while you don't. Your different directions of travel explain why, when your feet meet the floor again, they meet it in a slightly different place.

This is reasonably clear in my mind, but having just read that back, is not particularly clear in the words I've written. I guess this is why physicists use maths rather than words to describe things....

No, the floor doesn't push up, you push against it
the base of the bucket DOES NOT 'push up', it merely contains the water, preventing it's escape

If the ring were in vacuum, what would be accelerating you in the direction of the spin?

You are NOT being accelerated, you are contained within a pressurised ring
one, that is spinning in a vacuum (Space). You are moving at the same speed as the ring (ferris wheel) is spinning
BUT you will not perceive the movement of the ring unless you observe the stars via a porthole.
So, to you, the floor will be stationary, and, while the floor will follow the lines of the circumference
and will also disappear from view at a distance, to you it will seem like a FLAT surface
AND at 1g [earth type gravity] you will weigh as heavily as you do here on Earth