Can you stand on a frictionless plane?

[UtterMess]

A friend and I have had an ongoing discussion about whether or not it would be possible for a person to go from a prone position to a standing position on a frictionless surface. He says that it would be impossible while I say that, although difficult, it would be possible after some trial and error. All other variables are exactly like on earth, except the floor would be 100% frictionless. You can't use a wall or other object for aid. It has to be done solely with the human body. So, is it possible?

 

[lanman]

If you can assume the surface to be perfectly frictionless, then you can assume the human body to be perfectly coordinated and balanced too. It would have to aim its force down perfectly perpendicular to the surface, so that no component of it points horizontally, or somehow make sure that all horizontal forces cancel out.
If it gets too precise, would it then be subject to quantum uncertainty? How perfectly frictionless is the surface?

 

[t-money]

I think on the scale of a person you don't have to worry about quantum uncertainty. And what is it meant by a prone position?

 

[Danger]

Prone means lying down.
I suspect that an extremely talented gymnast might be able to pull it off; I know that I couldn't. Then again, I have trouble standing up on ice.

 

[UtterMess]

I think that you could make your body rigid enough to resist the horizontal forces. Look at a chair where the legs aren't perpendicualr to the ground. It's still able to maintain its shape and stand. It would be a similar situation with your arms or legs.

what is it meant by a prone position?

Prone means lying face down.

 

[rewebster]

If you can assume the surface to be perfectly frictionless, then you can assume the human body to be perfectly coordinated and balanced too. It would have to aim its force down perfectly perpendicular to the surface, so that no component of it points horizontally, or somehow make sure that all horizontal forces cancel out.

I might say it a little differently.

In that, where ever your center of mass is when laying down, the forces that make you rise must be all internal (within the body), the center of mass must rise perfectly perpendicularly to the (horizontal) surface from its original location----like a person on ice skates rising up after doing the 'splits'.

 

[rcgldr]

One possible sequence. Roll over onto your back. Use stomach muscles to sit up. Place both hands on right side, and bend both knees with lower legs to left side, with right knee close to left foot. Both hands, right knee and right ankle form a rectangle on the surface at this point, with the right lower leg on surface. Press down with right ankle to rotate and raise hips to end up on both hands, left knee, and side of right lower leg. Adjust left knee for balance with both hands by sliding it into place. Raise right knee and place next to left knee. You're know in a crawl position. Raise one leg and place foot (or ball of foot, depends on flexibility here) on ground. Balancing with two hands and the ball of one foot, raise other foot. Shift weight back so it's on both feet (or balls and toes of feet), and stand up, using arms for balance.

 

[DaveC426913]

the center of mass must rise perfectly perpendicularly to the (horizontal) surface from its original location

Well frankly - the centre of mass will rise prependicularly, whether the person wants it to or not. The frictionless surface will ensure that.

The only things that need to happen are
1] the centre of mass must stay inside the supports or he'll fall over
2] the person will probably have to have excellent muscle control - like your skater rising from the splits

 

[belliott4488]

UtterMess, I agree with you: difficult, but possible.

Ask your friend what's wrong with this: if you have sufficient strength, you will be stable if you support yourself at four points on the ground in such a way that your center of mass is directly over some point inside these four points (or inside the quadrilateral they define, to be a bit more precise) - think like a table with splayed legs. So, what you do first is to spread your arms and legs out "spread eagle" style, and then slowly bring them towards each other as you lift your body upwards (I said you'd need sufficient strength!). Eventually you'll be standing on your feet and hands, bent over, right? Now, if you slowly lean backwards until your center of mass is over a point contained within the quadrilateral defined by your toes and heels (i.e. another four points), and if you have a good enough sense of balance, you should be able to straighten up in a stable fashion, keeping that C-O-M over your feet. They might slide forward or backward as your C-O-M moves backward or forward, but who cares? The point is that you'll be stable.

 

[LURCH]

Yeah, what Belliott said. You have four points (heel and toes on each foot), so friction is not necessery. But for bonus points, could the person stand still (in one spot)?

 

[rewebster]

1] the centre of mass must stay inside the supports or he'll fall over

yep --I was just thinking without using any 'extra' energy, I guess

 

[ank_gl]

All other variables are exactly like on earth, except the floor would be 100% frictionless.

air drag?

 

[Capuchin]

That's what I was thinking ank, air resistance would be a great help to get you onto your feet.

 

[UtterMess]

UtterMess, I agree with you: difficult, but possible.

...So, what you do first is to spread your arms and legs out "spread eagle" style, and then slowly bring them towards each other as you lift your body upwards (I said you'd need sufficient strength!)...

You wouldn't even need to go that far. You could just do a pushup with your legs spread. Much easier and gets you into a similar ending position.

air drag?

Not sure how much of an effect it would have either way. It would slow you down if you started sliding, but that's about it.

 

[cks]

Conditions:

1)assuming, that person is standing inside a train, with all the windows closed, (so no air drag)
2)only floor and the human body contact

2 cases
1st case (train is accelerating)
the person cannot stand still on the floor, because there is no force acting on the person to make it accelerate with the train as well.

2nd case(train is traveling at a constant speed)
the person can stand still on the floor.

 

[cks]

the 2nd case is similar to what the UtterMass said, it's possible. consider the Earth as moving at a constant velocity in an absolute frame(which doesn't exist.)

 

[LURCH]

Conditions:

1)assuming, that person is standing inside a train, with all the windows closed, (so no air drag)
2)only floor and the human body contact

2 cases
1st case (train is accelerating)
the person cannot stand still on the floor, because there is no force acting on the person to make it accelerate with the train as well.

2nd case(train is traveling at a constant speed)
the person can stand still on the floor.

I agree. At first I thought, "the person could stand, but how could they keep one place without friction to hold them?" Then I realized that, without friction to propell them, the person actually couldn't move from their place! If we allow normal aerodynamic effects, then they could use the friction of the air to "swim" across the room, but if we had frictionless floors and frictionless air, then the person had better be within reach of a wall at the beginning. Even with frictionless air, floors and walls, a person would be able to move about, so long as they never found themselves at a dead stop relative to the room, with no walls within reach. In that state, the person would be trapped for ever.

 

[UtterMess]

Trapped yes, but still able to stand.

 

[DaveC426913]

Trapped yes, but still able to stand.

I'm not sure even frictionless air can ignore Newton's 3nd law. She may not be able to swim, but he can still generate propulsion. Turn head left, inhale; turn head right, exhale. Repeat.

 

[Danger]

Turn head left, inhale; turn head right, exhale. Repeat.

I didn't know that we were allowed to quote the 'Kama Sutra' here.

 

[cks]

I'm not sure even frictionless air can ignore Newton's 3nd law. She may not be able to swim, but he can still generate propulsion. Turn head left, inhale; turn head right, exhale. Repeat.

You make a point, you can move with inhalation and exhalation.

Imagine it this way, if you fart(just like a spaceship emitting its fuel), then you can move forward with the force pushing youequal to m*dv/dt of your gas.

 

[UtterMess]

so if you know you're going to be put on a frictionless surface, be sure to bring lots of beans and sauerkraut.

 

[rewebster]

I agree. At first I thought, "the person could stand, but how could they keep one place without friction to hold them?" Then I realized that, without friction to propell them, the person actually couldn't move from their place! If we allow normal aerodynamic effects, then they could use the friction of the air to "swim" across the room, but if we had frictionless floors and frictionless air, then the person had better be within reach of a wall at the beginning. Even with frictionless air, floors and walls, a person would be able to move about, so long as they never found themselves at a dead stop relative to the room, with no walls within reach. In that state, the person would be trapped for ever.

well, if you wanted to go one step farther even, I would bet that muscle contraction and the 'holding' of those muscles in place has facets of 'friction' in it--but the initial thread only states 'floor'

I'm not sure even frictionless air can ignore Newton's 3nd law. She may not be able to swim, but he can still generate propulsion. Turn head left, inhale; turn head right, exhale. Repeat.

wouldn't the 'inhaling' process cancel the 'exhaling' process?

 

[Danger]

wouldn't the 'inhaling' process cancel the 'exhaling' process?

No. You inhale in one direction, which will suck you forward, then turn your head 180° and exhale to provide thrust in the same direction.

 

[DaveC426913]

so if you know you're going to be put on a frictionless surface, be sure to bring lots of beans and sauerkraut.

Yep.
1] Sniff beans.
2] Say ew.
3] Throw beans.
4] Sniff sauerkraut
5] Say EW!
6] Throw sauerkraut - try to hit same spot as beans.

 

[keinve]

it would be possible, but unless you are a trained in the art of standing up without friction, you would get some bruises. at least.

 

[malty]

it would be possible, but unless you are a trained in the art of standing up without friction, you would get some bruises. at least.

Yeah, especially considering that frictionless air means nothing to slow down your fall, which brings me on nicely to my question, suppose this was an actual experiment, and suppose the experimenter was well padded (to help prevent those bruises from when s/he falls!) would that mean that they actually mean that they'd be obstructing the "frictionless" environment, because even though the plane is frictionless wouldn't interacting with the plane create somesort of friction?? Or would this be enough to actually have an effect?

Finally can I ask you guys/gals what you're visualing a frictionless plane to be like. My image is of a glass like plane and some poorhelpless chap feebly trying to crawl out of it., only that he can isn't moving anywhere.

 

[Hootenanny]

Finally can I ask you guys/gals what you're visualing a frictionless plane to be like. My image is of a glass like plane and some poorhelpless chap feebly trying to crawl out of it., only that he can isn't moving anywhere.

An ice rink in slippers is always a good place to start...

 

[malty]

An ice rink in slippers is always a good place to start...

oddly enough I've actually being in that situation before, though it was a local lake, so I don't know if there's much of a difference between a rink and a lake, but I must tell you that I thought the slippers were well *wow* surpisingly more efficent! No idea if was just me balance that day, or gum stuck onto the bottom of the slippers (it happens to me quite a lot!) but I found my balance no problem, and moving was like a breeze, there must have been something on the soles of those slippers... there had to have been.

 

[belliott4488]

oddly enough I've actually being in that situation before, though it was a local lake, so I don't know if there's much of a difference between a rink and a lake, but I must tell you that I thought the slippers were well *wow* surpisingly more efficent! No idea if was just me balance that day, or gum stuck onto the bottom of the slippers (it happens to me quite a lot!) but I found my balance no problem, and moving was like a breeze, there must have been something on the soles of those slippers... there had to have been.

Nah, slippers have low friction on floors, but I wouldn't expect them to be slippery on ice. The reason we slip on ice is that the pressure under our feet melts the ice a bit, and we actually slide on a thin film of liquid water. That why ice skates have thin blades; all the skater's weight is concentrated on an extremely small contact area, which means very high pressure, thus a lot of melting. With slippers, you're distributing your weight over a relatively large area, especially since slippers are soft and can flatten out, so there's relatively little melting. In fact, I wouldn't be surprised if what little melting occurred immediately refroze, making the ice feel "sticky", like an aluminum flag pole ...

 

[DaveC426913]

oddly enough I've actually being in that situation before, though it was a local lake, so I don't know if there's much of a difference between a rink and a lake, but I must tell you that I thought the slippers were well *wow* surpisingly more efficent! No idea if was just me balance that day, or gum stuck onto the bottom of the slippers (it happens to me quite a lot!) but I found my balance no problem, and moving was like a breeze, there must have been something on the soles of those slippers... there had to have been.

The slippers probably had a textured sole. And they're quite soft rubber. These lead to very good traction on ice.

Counter-intuitively, shoes and boots wouldn't work as well since they have much harder soles. (Think of shoes & boots like all-weather tires. Good in most normal conditions, but bad in specialized conditions. Slippers are bad in normal conditions, but work well for traction on hardwood floors and, it so happens, on ice.)

 

[TVP45]

You cannot. The principal reason is the postural sway algorithm used by your cerebellum. Sideways is not too hard; fore and aft is really, really hard for more than a few seconds (you can suppress the overcompensation control by actively thinking about it). Tried this on very good linear bearings - we all busted our butts.

 

[Rahmuss]

Nope. Not possible. If it's perfectly frictionless, then even laying down the overall vibration of the very atoms that makeup your body would cause you to start sliding one way or another and that would increase as an acceleration because there is nothing to slow it down; but plenty to speed it up. And you never said there wasn't air, so pretty soon it would be extremely hard to even try and stand because of the sheer wind factor. You would continue to accelerate; but you would run into a kind of free-fall limit (free-slide limit?) where the drag caused by the air molecules would ultimately cap your speed. Though if there was no air, then you could accelerate to the speed of light. The only problem is that time is stopped for you and since it takes time to try and stand up or even to apply brakes (wherever they came from) would not work because you don't have any time. :D

 

[belliott4488]

Nope. Not possible. If it's perfectly frictionless, then even laying down the overall vibration of the very atoms that makeup your body would cause you to start sliding one way or another and that would increase as an acceleration because there is nothing to slow it down; but plenty to speed it up. And you never said there wasn't air, so pretty soon it would be extremely hard to even try and stand because of the sheer wind factor. You would continue to accelerate; but you would run into a kind of free-fall limit (free-slide limit?) where the drag caused by the air molecules would ultimately cap your speed. Though if there was no air, then you could accelerate to the speed of light. The only problem is that time is stopped for you and since it takes time to try and stand up or even to apply brakes (wherever they came from) would not work because you don't have any time. :D

Well! How cool is THAT?! Who needs propulsion in space? We just go out there and the "overall vibrations" of our "very atoms" will cause us to accelerate without limit! There's "plenty to speed it up"! Free energy! Whoo-hoo!

 

[Rahmuss]

Hooray! :D Though, sorry to say, there actually is drag in space, it's not a complete vacuum. :(

 

[russ_watters]

Why would the vibrations of our atoms cause us to start moving? The vibrations are random in nature.

And no, the drag in space is negligible. There is only about one atom per cc of space.

 

[supraanimo]

One problem I see with standing on this is that the human body does not exert a force exactly perpendicular to the surface to remain balanced, therefore the horizontal component of those forces would tend to force the persons feet in a less than desirable direction.

 

[Rahmuss]

russ_watters - Correct, the vibrations are fairly random; but the overall effect would not be zero. I would guess that the points where there are large masses on your body that are touching the frictionless surface less (ie. your neck and head) would produce the greatest directional difference. And therefore you would probably start moving around somewhat randomly (very small motion, almost imperceptible) and then after time you would pick up speed and after awhile the force pushing back the other way would be negligible.

You have to realize that the overall net force by the vibrations of the atoms could not be zero, and that there would be one direction which overall would extend an overall greater force on your body and that's the direction you would end up going.

And as far as the drag in space you're right, it would take quite awhile; but you would get drag.


Nice pictures on your site by the way. I hope to get a nice telescope someday. Any suggestions?

 

[Loren Booda]

Russ - surely the best "home brewed" astrophotography I've come across, especially the galaxies. The choicest set up near DC is the University of Maryland observatory - but still too much haze and light pollution. Optics, imaging and mechanics are much improved since my viewing, mostly as a child.

 

[PatPwnt]

If you have atleast 3 limbs on the ground at all times, you wil not fall over. Its that simple. Well unless you are not strong enough to keep the limbs steady. If you have enough balance you can stand on two feet. I think standing on tiny marbles would be a better simulation than ice. Not sure.

 

[DaveC426913]

russ_watters - Correct, the vibrations are fairly random; but the overall effect would not be zero. I would guess that the points where there are large masses on your body that are touching the frictionless surface less (ie. your neck and head) would produce the greatest directional difference. And therefore you would probably start moving around somewhat randomly (very small motion, almost imperceptible) and then after time you would pick up speed and after awhile the force pushing back the other way would be negligible.

You have to realize that the overall net force by the vibrations of the atoms could not be zero, and that there would be one direction which overall would extend an overall greater force on your body and that's the direction you would end up going.

First of all, what you would get is a random walk. If we grant that the vibrations of your atoms could generate macroscopic movement then you wouldn't get a preponderance of movement in one direction, and it wouldn't accelerate. You'd get each random movement acting, resulting in a random walk.
And second of all, I would want to see a rationalization that atomic-scale vibrations could generate macroscopic displacement, because I'm not convinced it would.

 

[TVP45]

If you have atleast 3 limbs on the ground at all times, you wil not fall over. Its that simple. Well unless you are not strong enough to keep the limbs steady. If you have enough balance you can stand on two feet. I think standing on tiny marbles would be a better simulation than ice. Not sure.

That works OK for inanimate objects, but not for humans. In general, we use an active postural control where we lean slightly forward, correct, then slightly backwards, and so on. (I've simplified that but the idea is OK).
Tom

 

[Rahmuss]

PatPwnt - Yep, you could; but you would have to keep adjusting your three contact points because they would want to keep sliding. And that's not really standing up as the question was asking.

DaveC426913 - So you are saying that every atom in our body would vibrate with the exact same force, no matter what pressure is applied to it and not matter what kind of atom it is? That seems a bit ridiculous doesn't it? Heck, since they didn't say that there was no air, then even breathing in one direction continuously could start you moving. Again, it would be very small; but a completely frictionless surface... man you'd keep accelerating until the drag force of the air capped your speed. I guess that's what I want for my birthday. :D An endless frictionless flat surface (and a way to get off it).

 

[TVP45]

PatPwnt - Yep, you could; but you would have to keep adjusting your three contact points because they would want to keep sliding.

But, you cannot adjust your three contact points. There is nothing to push against. I have included a link to a paper by Bob Peterka, one of the world's leading researchers on postural control. It has a fairly comprehensive reference list of other papers as well. If you are interested further, you might also look at some of the work coming out of Mark Redfern's group at the University of Pittsburgh where they are looking at how you incorporate feedback from the slipperiness of the floor into an anticipatory response.

http://jn.physiology.org/cgi/reprint/93/1/189?ijkey=ddade5a6728e67aa15167a92eed59027761e20c0

 

[Rahmuss]

TVP45 - I should have clarified my point a bit more. The adjustments I'm referring to are simply flexing your muscles, bending your waiste, bending your arms and knees, pulling your arms down more in front of you or pushing them up. You could still make all those movements. Indeed there would be less resistence because there is no friction from the surface contact. Imagine a man (this time on all fours - hands and feet) on very slippery ice. He can use his muscles to pull his limbs closer together in a tighter formation, or relax them a bit and let gravity move his limbs, spreading them out, away from each other.

 

[Loren Booda]

The ability to stand upright on a frictionless surface with one or two "legs" overall, for more than the time it takes to fall, is statistically extremely improbable and initially nonlinear in character, like balancing a pencil on its point.

 

[TVP45]

TVP45 - I should have clarified my point a bit more. The adjustments I'm referring to are simply flexing your muscles, bending your waiste, bending your arms and knees, pulling your arms down more in front of you or pushing them up. You could still make all those movements. Indeed there would be less resistence because there is no friction from the surface contact. Imagine a man (this time on all fours - hands and feet) on very slippery ice. He can use his muscles to pull his limbs closer together in a tighter formation, or relax them a bit and let gravity move his limbs, spreading them out, away from each other.

Yes, I see your point. You can indeed kneel ifyou're careful. I thought you were referring to standing but, as I reread your post, you clearly were not. My apologies.
Tom

 

[rewebster]

No. You inhale in one direction, which will suck you forward, then turn your head 180° and exhale to provide thrust in the same direction.

but wouldn't the 'inhaled breath' hit the back of the throat?--

 

[DaveC426913]

... you would have to keep adjusting your three contact points...

You wouldn't so much keep adjusting them as you would keep them rigid. In theory, if your leg muscles were strong enough, you could plant your feet a metre apart and still stay upright (skaters and cheerleaders can do this). You would not have to "keep adjusting" anything - likewise, a perfectly solid statue of a man would stand like this just fine with no sliding.

DaveC426913 - So you are saying that every atom in our body would vibrate with the exact same force, no matter what pressure is applied to it and not matter what kind of atom it is? That seems a bit ridiculous doesn't it?

Yes it does. Which is why I never said anything of the sort.

The atoms in your body can do whatever they want - great gooey gobs of them could all leap 2 inches to the left if they want. It will not affect the location of your centre of mass. And it will not create any net movement of your centre of mass.

Heck, since they didn't say that there was no air, then even breathing in one direction continuously could start you moving.

Yes, we've already dealt with the breathing thing. Breathing is a propulsive force, and it ejects mass from your body - completely different from internal forces.

Again, it would be very small; but a completely frictionless surface... man you'd keep accelerating until the drag force of the air capped your speed.

No, you would not keep accelerating. As you breathe in and out, you'd move first forward, then back on each breath, resulting in no net movement over time.

What you could do though, is turn your head between inhalation and exhalation. Then you would get net movement. (Of course, that would work only in principle. Since your bosdy turns in the opposite direction to your head, you'd have to turn your head well past 180 degrees in one direction to get your "exhaust port" re-pointed along your axis of movement. Either that or you'd have to settle for either a circular path or a s-curved path.)



I am dubious about your top speed though. Seems to me it'll limited by your exhaust velocity (your breath) before it'll be limited by air friction on your body. I think it would cap out when your exhaust velocity (again, your breath) equals the apparent wind. i.e. If you can breathe a column of air moving 4mph, then your velocity would plateau when the surrounding air is moving relative to you at 4mph.

 

[DaveC426913]

but wouldn't the 'inhaled breath' hit the back of the throat?--

Remember why air is going into the mouth - a low pressure area is created in the lungs.

That low pressure is transferred to the volume in front of your face by way of your throat. So the air in your throat is under lower pressure, not higher pressure. And your body is pushed into that low pressure area by the higher pressure behind your head.


When a fan sucks air through itself, does the air "hit" the back of the fan blades propelling the fan forward? No. The fan is pushed backward into the partial vacuum.