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Author Topic: Just for fun - a brain teaser - how do they do it?  (Read 33420 times)
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img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #75 on: 2012-03-08, 01:03:53 »
Group: Guest
Hi all,

I've performed an experiment today.  A ball is point contacted with a friction surface.  The surface is being pull left or right.  I used a marble and a square container.

The result was when the surface move, the marble move and roll, when the surface stop moving, the marble also stop moving.  I still needs confirmation that this is the result but I'm very certain it is.  Now the question is this:  Why does the marble stop and has no residue motion?  

This is quite a fascinating experiment to me.
   
img  BEP
Re: Just for fun - a brain teaser - how do they do it? « Reply #76 on: 2012-03-08, 02:23:49 »
Group: Guest
I can't imagine how you see those results.

The momentum in the rolling ball would be angular but it is still momentum. When the friction surface is stopped abruptly that angular momentum should be converted to linear motion.
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #77 on: 2012-03-08, 02:42:56 »
Group: Guest
Quote from: WaveWatcher on 2012-03-08, 02:23:49
I can't imagine how you see those results.

The momentum in the rolling ball would be angular but it is still momentum. When the friction surface is stopped abruptly that angular momentum should be converted to linear motion.



I know huh, this is why I conclude Bessler was for real. lol
   
img  MileHigh
Re: Just for fun - a brain teaser - how do they do it? « Reply #78 on: 2012-03-08, 02:55:46 »
Group: Guest
Gibbs:

The answer is as follows.  We are assuming that the ball never slips when you move the surface.

There are three phases to your experiment.

1.  You accelerate the surface.
2.  The surface is moving at a constant velocity.
3.  You decelerate the surface.

During phase 1, you impart angular momentum to the ball because you are applying torque to the ball simply because the surface is accelerating.  Therefore the rotating ball has rotational energy R associated with it at the end of the acceleration.

During phase 2, the ball is rolling on the moving surface.  The rotational energy remains constant at a value of R.

During phase 3, you remove angular momentum from the ball because now you applying torque on the ball that is in the opposite direction of the ball's rotation.  The amount of rotational energy that you remove from he ball at the end of the deceleration phase is is also R.

Therefore, rotational energy of the ball goes from zero to R and then back to zero.   Thus the ball stops rolling.

MileHigh
   
img  BEP
Re: Just for fun - a brain teaser - how do they do it? « Reply #79 on: 2012-03-08, 03:17:41 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-08, 02:42:56
I know huh, this is why I conclude Bessler was for real. lol



What a shame  >:(

All the time since I was a toddler I thought my toy cars weren't special. You know, the ones that throw sparks with the inner flywheel spinning after you scoot them across the floor?

They were special  :) They should have stopped when I placed them on the floor after spinning them up !  Now, I think I may have some difficulty finding one of those for use in free energy research.  :'(
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #80 on: 2012-03-08, 03:37:18 »
Group: Guest
Quote from: MileHigh on 2012-03-08, 02:55:46
Gibbs:

The answer is as follows.  We are assuming that the ball never slips when you move the surface.

There are three phases to your experiment.

1.  You accelerate the surface.
2.  The surface is moving at a constant velocity.
3.  You decelerate the surface.

During phase 1, you impart angular momentum to the ball because you are applying torque to the ball simply because the surface is accelerating.  Therefore the rotating ball has rotational energy R associated with it at the end of the acceleration.

During phase 2, the ball is rolling on the moving surface.  The rotational energy remains constant at a value of R.

During phase 3, you remove angular momentum from the ball because now you applying torque on the ball that is in the opposite direction of the ball's rotation.  The amount of rotational energy that you remove from he ball at the end of the deceleration phase is is also R.

Therefore, rotational energy of the ball goes from zero to R and then back to zero.   Thus the ball stops rolling.

MileHigh

Thanks MH,

But I think you're still in the category as WW thought.  During phase 2, the ball is rolling on the surface, so as long as you stop the surface, the ball will shoot the other way and stay rolling. 

During phase 1, the ball gain angular momentum, but it also gain linear momentum.  Now that's cool. lol 

   
img  EMdevices
Re: Just for fun - a brain teaser - how do they do it? « Reply #81 on: 2012-03-08, 15:54:27 »
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Posts: 805
Gibs , like MH said all forces are opposite upon deceleration, so if there is no slippage, the marble will come to rest, but if you decelerate faster then you accelerated, and overcome the static friction, the ball will roll like you were expecting.

Guys, I see there's speculation that compressed air is used, and that's a very sad and a pathetic conclusion considering the fact that the experiment is not an OU experiment.  So whenever we don't understand something we fall back to simpler concepts?  For example a TPU has to have powerful batteries inside, right?  or a obviously heavy metallic boat must have underwater "legs" that's why it does't sink?  Lol

EM
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #82 on: 2012-03-08, 16:52:00 »
Group: Guest
Quote from: EMdevices on 2012-03-08, 15:54:27
Gibs , like MH said all forces are opposite upon deceleration, so if there is no slippage, the marble will come to rest, but if you decelerate faster then you accelerated, and overcome the static friction, the ball will roll like you were expecting.


EM

I know, but when you pull the surface to the right, the ball rotate left but also moving right.  The rotational energy is exactly equal the translational energy. 

   
img  Harvey
Re: Just for fun - a brain teaser - how do they do it? « Reply #83 on: 2012-03-09, 04:39:43 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-08, 01:03:53
Hi all,

I've performed an experiment today.  A ball is point contacted with a friction surface.  The surface is being pull left or right.  I used a marble and a square container.

The result was when the surface move, the marble move and roll, when the surface stop moving, the marble also stop moving.  I still needs confirmation that this is the result but I'm very certain it is.  Now the question is this:  Why does the marble stop and has no residue motion?  

This is quite a fascinating experiment to me.

Hi Gibbs,

What do you think would happen if the ball were much heavier and the friction surface was sufficiently long so that when you pulled it fast the ball rotated in place as the sheet was moved under it. Assuming we never lose friction, what would happen when you instantly stop pulling the sheet?

I think it would roll off in the opposite direction that you pulled the sheet. Hmmm, I wonder if this could be modeled in PHUN (aka Algadoo)  :) . . .
   
img  exnihiloest
Re: Just for fun - a brain teaser - how do they do it? « Reply #84 on: 2012-03-09, 10:22:41 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-05, 14:05:48
...
imagine a disk turning another disk through gear coupling.  If you take a picture at time t and at time t+1, they both are identical.  We can argue that a source is powering one of the disk, but the source is only providing a torque/force just like gravity argument. 

Not correct.  You could say this, only if there are losses due to friction or if there is a useful work extracted elsewhere in the system.
Otherwise there is no reason for such rotating disks to stop after having been put in motion and no need for force to maintain the rotation.
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #85 on: 2012-03-09, 13:43:20 »
Group: Guest
Quote from: exnihiloest on 2012-03-09, 10:22:41

Not correct.  You could say this, only if there are losses due to friction or if there is a useful work extracted elsewhere in the system.
Otherwise there is no reason for such rotating disks to stop after having been put in motion and no need for force to maintain the rotation.




I assumed that friction was presented, that's the only reason for cause of motion.
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #86 on: 2012-03-09, 13:52:35 »
Group: Guest
Quote from: Harvey on 2012-03-09, 04:39:43
Hi Gibbs,

What do you think would happen if the ball were much heavier and the friction surface was sufficiently long so that when you pulled it fast the ball rotated in place as the sheet was moved under it. Assuming we never lose friction, what would happen when you instantly stop pulling the sheet?

I think it would roll off in the opposite direction that you pulled the sheet. Hmmm, I wonder if this could be modeled in PHUN (aka Algadoo)  :) . . .

Hi Harvey,

I've seen you work with PHUN.   I hope it can be modeled.   I think it's impossible for the ball to rotate in place without moving in the direction of pulling.  Because the energy of moving and rotation are equal, they will come to a stop.  If rotation energy is more, it will roll off in the opposite direction, and if the translation is more, it will roll off in the direction of pulling.  I've seen both in experiment and analysis that they are of equal.  You can imagine a force diagram.  The force that makes the ball rotate is the same force that makes it move in the direction of pulling.  It's the friction force at surface contact.  They act on the ball to move and rotate at equal amount of time. 

   
img  exnihiloest
Re: Just for fun - a brain teaser - how do they do it? « Reply #87 on: 2012-03-09, 16:50:23 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-09, 13:43:20

I assumed that friction was presented, that's the only reason for cause of motion.



What do you mean? Friction is cause of stopping rotation, not the contrary. If you mean that there must be a cause of motion because there is friction and the cause have to overcome the friction, I agree.
Now, back to the reason of this question. If you take a photo at t and another at t+1 and you see the same state, then your system is not closed (it has radiated the heat from friction). If it is closed the photo of the state of the system shows that the temperature has increased between t and t+1, the state has changed. This is what I said in Reply #51.
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #88 on: 2012-03-10, 01:20:15 »
Group: Guest


Oh man, what the heck.   lol
   
img  Harvey
Re: Just for fun - a brain teaser - how do they do it? « Reply #89 on: 2012-03-10, 04:53:51 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-09, 13:52:35
Hi Harvey,

I've seen you work with PHUN.   I hope it can be modeled.   I think it's impossible for the ball to rotate in place without moving in the direction of pulling.  Because the energy of moving and rotation are equal, they will come to a stop.  If rotation energy is more, it will roll off in the opposite direction, and if the translation is more, it will roll off in the direction of pulling.  I've seen both in experiment and analysis that they are of equal.  You can imagine a force diagram.  The force that makes the ball rotate is the same force that makes it move in the direction of pulling.  It's the friction force at surface contact.  They act on the ball to move and rotate at equal amount of time. 



I actually made a short film with my cellphone that demonstrates this. But, in my case I used a sheet of paper and a roll of masking tape, but it does perform as stated. The roll begins rotating in place and then when the paper reaches the end (or stops, same difference) the tape rolls off in the other direction.  :)
   
img  GibbsHelmholtz
Re: Just for fun - a brain teaser - how do they do it? « Reply #90 on: 2012-03-10, 14:43:07 »
Group: Guest
Quote from: Harvey on 2012-03-10, 04:53:51
I actually made a short film with my cellphone that demonstrates this. But, in my case I used a sheet of paper and a roll of masking tape, but it does perform as stated. The roll begins rotating in place and then when the paper reaches the end (or stops, same difference) the tape rolls off in the other direction.  :)

Hm... It doesn't work for me.  Unless you have a bias upward component when pulling, it shouldn't happens. 

   
img  Harvey
Re: Just for fun - a brain teaser - how do they do it? « Reply #91 on: 2012-03-11, 07:54:00 »
Group: Guest
Quote from: GibbsHelmholtz on 2012-03-10, 14:43:07
Hm... It doesn't work for me.  Unless you have a bias upward component when pulling, it shouldn't happens. 



You are correct, I do have that bias.  :P

However, if we replace that bias with a very large linear inertia combined with a relatively small moment of inertia (long thin heavy rod), then we should be able to experience it with little or no upward bias.

In this case, the objective is to convert the energy to rotational motion without a linear translation - so we use the inertial mass of the rod as an anchor against linear translation, but we use the small diameter to minimize the MOI.

At some point, the traction, speed of acceleration and geometries just mentioned should intersect and allow the rod to remain in place (or very near the starting point) as it is accelerated rotationally.

At least that's my perspective on it  :)
   
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