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### Topic: The spinning tube trick. (Read 4910 times)previous topic - next topic

#### GoForSmoke

##### Mar 28, 2013, 12:38 pmLast Edit: Mar 29, 2013, 01:15 am by GoForSmoke Reason: 1
This is a goodun! It got me, I had to watch the answer video and say OOOHHHHH! But then, I'm not so bright any more.

Bon apetit!

Spoiler alert -- it's explained below.

BTW, this has all the makings of a good bar trick. Might be worth a free beer.
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

#### Boffin1

#1
##### Mar 28, 2013, 12:53 pm
Got me too !
45 years of editing projects with a knife and soldering iron, then I found Arduino !

#### liudr

#2
##### Mar 28, 2013, 11:56 pm
Photograph a bike wheel in motion, which portion is most clear?

#### Boffin1

#3
##### Mar 29, 2013, 12:11 am
What got me was that it appears to rotate about its centre, the slomo shows how it works though
45 years of editing projects with a knife and soldering iron, then I found Arduino !

#### liudr

#4
##### Mar 29, 2013, 12:42 am
I didn't see the solution but I thought the tube rotates forward on the table while the pressed end also rolls along the tube long axis backwards. The resultant velocity is slow enough so you will see the pressed end and its symbol. The other end has roll and rotation added together so that end is fastest of the tube and you won't see it, just like the top of a bike wheel is blury but bottom is clear.

#### liudr

#5
##### Mar 29, 2013, 12:59 am
Ok just watched the solution and under glass video. I can't understand the under glass result. Maybe the lack of friction but I thought the conclusion was not conclusive.

#### GoForSmoke

#6
##### Mar 29, 2013, 01:19 am

Ok just watched the solution and under glass video. I can't understand the under glass result. Maybe the lack of friction but I thought the conclusion was not conclusive.

XD Okay wise guy, try this one:
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

#### liudr

#7
##### Mar 29, 2013, 04:59 am
This second one is hard without looking at a solution. This behaves similar to water in a spinning bucket, where center of mass moves upwards. I'm not sure how to explain this one.

#### GoForSmoke

#8
##### Mar 29, 2013, 11:25 am
Quote
This behaves similar to water in a spinning bucket, where center of mass moves upwards.

Easy to intuit that added energy must do something. Now hold the bucket steady and spin the stars... I'm sure there's a version of that involving the hair of a blonde while the world turns around her.

Quote
I'm not sure how to explain this one.

Neither did the PHD physics teacher! He was able to break it down a bit on ice though.

2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

#### liudr

#9
##### Mar 29, 2013, 04:18 pm
We have a few those PHD types at work. I will see if there are any takers for this question. You can't spin stars. Only bucket. Since you can tell you are spinning or not spinning, spinning or not can't be taken as relative as you move forward and stars move backward.

#### liudr

#10
##### Mar 29, 2013, 04:34 pm
A paper discussing this:

http://physics.umd.edu/lecdem/services/refs_scanned_WIP/3%20-%20Vinit%27s%20LECDEM/D501/6/AJP000012.pdf

Seems dense.

#### GoForSmoke

#11
##### Mar 29, 2013, 05:52 pm

We have a few those PHD types at work. I will see if there are any takers for this question. You can't spin stars. Only bucket. Since you can tell you are spinning or not spinning, spinning or not can't be taken as relative as you move forward and stars move backward.

If the bucket or stars spin is an old philosophy thought-experiment, I think from before 1900.

2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

#### liudr

#12
##### Mar 29, 2013, 06:25 pm
There was also some thought back around that time that you can't do space travel since your vessel will have nothing to push against

#### GoForSmoke

#13
##### Mar 29, 2013, 07:31 pm
I think you should see what the discussion was and get the context before making judgements. Those were people ahead of their time starting to think in relative terms when so many were absolutists.

I am sure that there were people who understood the 2nd law of motion even before 1900.

2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

#### liudr

#14
##### Mar 29, 2013, 09:10 pm
Not all that interested in every piece of history in science. May look it up sometime. The tube trick was well received by a few colleagues and my lab classes. I like it better than the disk. It's not hard to explain and by explaining it the second time I found the answer to the under glass question. The video makes sense to me now.

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