1. ## Cognac

Jezza Bear's was in his shed cooking up some plans for the latest Kitchen Table Science project and was looking at cogs and wheels.

Now he wanted to get a cog A with a diameter of Y to roll around a cog B with a diameter of 2Y. His pencil kept on snapping when doing the calculations and had to ring up Al Bear to answer the question.

"How many turns about its own axis does cog A make when it rolls around cog B twice?"

Al Bear wasn't at home, he was down the pub! can you help JB please?

2. ## Re: Cognac

<img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15> <span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">4</span hide> <img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>

3. ## Re: Cognac

DARN - John got there first <img src=/S/thumbup.gif border=0 alt=thumbup width=15 height=15>

<img src=/S/whisper.gif border=0 alt=whisper width=29 height=17><small>At least I think his answer is correct</small>

4. ## Re: Cognac

Again

Scott and John are wrong <img src=/S/evilgrin.gif border=0 alt=evilgrin width=15 height=15>

There is a twist <img src=/S/pun.gif border=0 alt=pun width=22 height=18> in this one <img src=/S/evilgrin.gif border=0 alt=evilgrin width=15 height=15>

5. ## Re: Cognac

A TWIST Huh ?!?!?

<img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15> <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15> <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15> <span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">Head really hurting now </span hide>
<hr>"How many turns about its own axis does cog A make when it rolls around cog B twice?"<hr>
Presume Cog B is stationary and Cog A now does all the work ... <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15> <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15> <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15>
<span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">Answer is Zero since Cog A is rolling AROUND Cog B and Axis is moving at same time ?!?!?!?</span hide>

6. ## Re: Cognac

<img src=/S/nope.gif border=0 alt=nope width=15 height=15> <img src=/S/innocent.gif border=0 alt=innocent width=20 height=20>

7. ## Re: Cognac

To <img src=/S/yawn.gif border=0 alt=yawn width=15 height=15> to stayyyyyyyyy <img src=/S/woops.gif border=0 alt=woops width=58 height=36> <img src=/S/snore.gif border=0 alt=snore width=32 height=15>

8. ## Re: Cognac

About <span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">6.2831853</span hide> times?

9. ## Re: Cognac

<img src=/S/bananas.gif border=0 alt=bananas width=33 height=35>

<span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">6 would have done</span hide>

Have a very large [cognac] and a [choccy bar]

10. ## Re: Cognac

<img src=/S/confused.gif border=0 alt=confused width=15 height=20> can you let me in on the secret? <img src=/S/whisper.gif border=0 alt=whisper width=29 height=17>

11. ## Re: Cognac

I expected cog B to be hollow, and cog A actually *inside* cog A.

12. ## Re: Cognac

This is my take

The outer cog is rotating around the larger cog. So if it starts at 12 O'Clock (say) and goes around once to return to 12 O'clock it has spun twice but also revolved around itself once so doing it twice it revolves <span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">6 </span hide>times <img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>

13. ## Re: Cognac

Thangyou , ani'll avanother glass ifimay <img src=/S/nuts.gif border=0 alt=nuts width=15 height=15>

14. ## Re: Cognac

sorry, but I don't get it <img src=/S/shrug.gif border=0 alt=shrug width=39 height=15> in one revolution, it has revolved around itself twice - as the earth revolves around itself 365x in a full year (360 degrees around the sun - which is a seperate revolution). A full revolution is 360 degrees about a fixed axis and it can't revolve around itself more than it has... revolved around itself. I thought the fixed axis (maybe it can be called the reference frame axis?) was the middle of the smaller cog. In other words - cog a's axis had 4 revolutions, and cog b's axis had 2 revolutions - but these aren't things that add.

i'm probably just missing the point of this. i'll blame it on my engineering classes.

15. ## Re: Cognac

I am configurating a flange and gromit on my system at the moment , when I get home I will get Al Bears email with the answer

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