# Can you stand on a frictionless plane?

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?

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?

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
Gold Member
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.

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.

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
Homework Helper
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
Gold Member
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

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

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)?

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

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

air drag???

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

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 thats about it.

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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 travelling at a constant speed)
the person can stand still on the floor.

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 travelling 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.

Trapped yes, but still able to stand.

DaveC426913
Gold Member
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.

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Danger
Gold Member

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

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.

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

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?

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Danger
Gold Member
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
Gold Member
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.