Can you stand on a frictionless plane?

[disregardthat]

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.

,
was said some pages back.

Even if the surface under you is accelerating it wouldn't mean anything since it is frictionless, right? The same properties stays true.

 

[russ_watters]

russ_watters - So, let's make the atoms into coins. I'm not sure how many billions of coins that is; but what you're saying is that flip all those coins and they will exactly balance out?

Not exactly, but the more you flip the closer they are likely to get to exactly balancing out, percentagewise.

 

[DaveC426913]

And, that is the question I answered. It is not possible, although a few trained athletes, e.g., skiers, who use knee and hip strategy can probably do it for perhaps 15 or 20 seconds.

How can you, in a single sentence, claim something is not possible and then immediately explain the circumstances in which it could, in fact, be done?

Possible means possible.

 

[DaveC426913]

As you move your arms in and out you hit the rubber balls at times, and that would push you back. See what I mean.

Yes, by moving your limbs, you can act upon the air. You are effectively swimming.

But you will only make headway if you coordinate your movements. Otherwise you will go nowhere.

Actually, that's not quite true. You will perform what is called a random walk.

Now the question is just if the outer atoms which makeup your body, would be exactly equaled out by the force they exert on the air molecules. Now if you had a perfectly symmetrical object, then they should equal out; but our bodies are not perfectly symmetrical.

Non-symmetricality does NOT lead to non-symmetrical forces.

Think of an abandoned rowboat in a lake that has no current. The random forces of the water do not cause the rowboat to start moving. If this were true, you would have discovered a free energy source.


BTW, this is not just theory. A few years back, when nanotechnology came into the fore, someone invented a nano-scale motor-ratchet device that took advantage of the very forces we are speaking of, namely, Brownian motion. The idea was that the random motions of molecules bouncing off the device could be used to turn the axle, but a ratchet converted the random motion into a one-direction turn rather than simply a back-and-forth motion.

Indeed, if the device had worked, they would have invented a perpetual motor. Alas, physicists using Newton's laws of motion were able to demonstrate that the device could not work.

 

[Rahmuss]

Jarle - True, if the frictionless surface below you was accelerating it would make no difference. I haven't read the post you reference; but it sounds like they might be trying to add mass to make it easier to stand. That would have null effect as far as I can tell.

russ_watters - True; but those forces on the outside of the body touching the frictionless surface and exerting a force in any kind of downward angle (except exactly down) would have null effect. Whereas the forces on the outside that are not touching the frictionless surface are in essence the only ones we need to pay attention to. Now with a completely symmetrical body you would have the same amount of force exerted everywhere; but thankfully my body is not a perfectly symmetrical object and so the balance would already be tilted.

 

[Rahmuss]

DaveC426913 - Well, then maybe I'm wrong; but it seems (and this is an exageration to display the point) that if you have 100 arms on one side hitting flying balls and only 50 arms on the other side, then you would start moving in the direction where the 50 arms are pushing because their overall force is canceled out by 50 arms from the other direction; but then there are still 50 more arms. I guess the object would not only have to be symmetric; but also of uniform elemental makeup.

P.S. I enjoy discussing this with you all. It makes me think.

 

[DaveC426913]

DaveC426913 - Well, then maybe I'm wrong; but it seems (and this is an exageration to display the point) that if you have 100 arms on one side hitting flying balls and only 50 arms on the other side, then you would start moving in the direction where the 50 arms are pushing because their overall force is canceled out by 50 arms from the other direction; but then there are still 50 more arms.

Yes, that's the coordinated part - 50 arms all pushing against the air in one direction.

Replace the 50 arms with one fan-shaped membrane, and the air with water - and you've got a swimming fish.