Will a Ball Stop in a Frictionless, Airless Tube?

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Discussion Overview

The discussion revolves around the hypothetical scenario of a ball rolling in a frictionless, airless tube that bends at the end and connects to a long pipe. Participants explore the implications of friction and sound energy loss on the ball's motion within this setup.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the ball will stop due to sound energy loss when it hits the surface, despite the assumption of a frictionless environment.
  • Another participant argues that if the ball is thrown down the pipe, it will keep rolling without resistance, but clarifies that sound production is part of friction.
  • Several participants assert that a ball cannot roll in a frictionless environment, suggesting it would only slide instead.
  • One participant explains that rolling requires friction, as it allows the ball to 'topple over' the part in contact with the surface.
  • Another participant notes that if the ball was already rolling before entering the tube, it would continue to roll due to the absence of stopping forces.
  • Some participants discuss the concept of frictionlessness, suggesting it may not be physically realizable and that even deep space has some resistance.
  • There is a mention of vacuum fluctuations and the implications of motion in a cosmic context, raising questions about resistance in space.

Areas of Agreement / Disagreement

Participants generally disagree on the implications of a frictionless environment for the ball's motion, with multiple competing views on whether the ball can roll or will only slide. The discussion remains unresolved regarding the feasibility of a truly frictionless scenario.

Contextual Notes

Participants express uncertainty about the physical realization of a frictionless environment and the effects of sound energy loss, highlighting limitations in assumptions about the scenario.

saikrishnadee
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Hey i have a doubt . i have not tried this experiment but i wanted to know what would happen. If we take a tube bending at the end and joining to a 5 km long pipe which is frictionless (assume) and there is no air to offer air resistance . So when i start rolling the ball will it stop or not . You might tell no but please take into consideration about the ball hitting the surface and producing a sound and hence losing energy.Even if the fiction is not hitting the object , the object should also be hitting the surface ( Every Force has equal an opposite reaction) . Please tell with reasons
 
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Assuming that you take a ball and throw it down the 5km long pipe (what is the bent tube at the start for?) which is frictionless, than the ball will keep rolling with no resistance. The 'ball hitting the surface and producing sound' is part of what we call friction (unless the ball is bouncing in the tube, but I assume it is just rolling).

The ball is touching the surface and produces a force on it (it's weight). The surface pushes back with a equally strong but opposite force (which is called the normal force). But if the pipe is completely straight (no bumps etc) and horizontal, then this normal force only acts vertically and thus cannot make the ball move faster or slower horizontally.
 
It can't roll if it is frictionless :)
 
Yep that's something I didn't even think about lol... Oh well, just replace 'roll' with 'slide' in my post then :p
 
Denton said:
It can't roll if it is frictionless :)
Anyway my question is incomplete ! the bending tube is attached to a long pipe which is 5 km and i hope the rest is correct


How is this possible ? Why won't it roll ?

Thanks
 
Denton said:
It can't roll if it is frictionless :)

How is that posibble can u explain a liitle more about it ?
 
For a ball to roll it needs friction on the surface that it's rolling on.

Think of it like this: Imagine you slide a ball across some surface. Because the surface causes a little friction on the part of the ball touching the ground, that part is slowed down. However, the rest of the ball 'topples over' the part on the ground: the ball starts to roll.

Now, when that surface is frictionless (think of an extremely slippery ice for example), there is nothing to slow the part of the ball touching the ground down, and the ball does not roll. It only slides over the surface.
 
Thanks a lot !
 
Nick89 said:
For a ball to roll it needs friction on the surface that it's rolling on.

Think of it like this: Imagine you slide a ball across some surface. Because the surface causes a little friction on the part of the ball touching the ground, that part is slowed down. However, the rest of the ball 'topples over' the part on the ground: the ball starts to roll.

Now, when that surface is frictionless (think of an extremely slippery ice for example), there is nothing to slow the part of the ball touching the ground down, and the ball does not roll. It only slides over the surface.


If the ball was already rolling before it entered the frictionless tube (perhaps because of the initial gradient), it would continue to roll, since no force would be acting on it to stop it rolling.
 
  • #10
brewnog said:
If the ball was already rolling before it entered the frictionless tube (perhaps because of the initial gradient), it would continue to roll, since no force would be acting on it to stop it rolling.

True. But I took the original post as a 'reference' as to how the ball would be made to move: by a bent tube. I can remember from another thread that even a ball falling down a frictionless slope would not roll and hence the ball will not roll for the entire length of the tube (assuming ofcourse that the person who dropped the ball in didn't give it a slight rotation to start it rolling...)
 
  • #11
It sounds like a ball in a frictionless tube would basically act like a ball floating in space. Even if the bend in the beginning got it to spin, the spin would have nothing to do with the frictionless part of the tube.

The idea of "frictionlessness" sounds like it may not be physically possible unless many restrictions are placed on the ball.
 
  • #12
No, a frictionless environment is impossible to realize. Even in deep space there still is some resistance, because there is also no such thing as a perfect vacuum.
 
  • #13
In deep space? Does that mean that you can crash into vacuum fluctuations until you stop? That would seem to imply a cosmic reference point of motion, which I thought wasn't possible.

Or is it more like a galactic "atmosphere", where a high pressure zone would mean one hydrogen atom per cubic inch?
 
  • #14
Even if there is only one particle you bump into, that is already some resistance.
I don't know how many particles there are in deep space, but I'm sure there's more than zero...
 

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