so one things clear that moon does not rotate about its own axis??

Well, here's my two cent's worth ...

The moving coin manifestly makes two full revolutions in the direction in which its centre moves.

Further to confuse the waters, I would assert that one of these revolutions is about its own axis, and one is not.

The motion can be broken down into two operations.

(a) Glue the two coins together at their initial tangential contact point, and rotate that combined object clockwise around the centre of the "stationary" coin.

(b) Break the glue connection, and rotate the "stationary" coin anticlockwise to put it back into its initial position. This drives the other coin as a gearwheel around its own axis to make another clockwise rotation.

Combining the motions, the moving coin makes one full rotation due to the "synchronous" rotation of its centre around the other, plus one full rotation around its own axis due to the tangential drive.

Incidentally, James Watt used this precise arrangement of gears to connect the oscillating piston of his steam engines to a rotary shaft, because James Pickard had already patented the (more familiar) crank drive. Most appropriately, it is called a "Sun and Planet" gear.

Good Grief PP, trust you with just two cents to supply the "sound of waters shaken".  ;-)

I wonder who in the forum agrees with you that the moving coin manifestly makes two full revolutions in the direction in which its centre moves. After all, both the coins have the same circumference, right? And each point on each coin touches the corresponding point on the other coin, right? And touches it just once, right? And in rolling the distance of its own circumstances surely the coin rotates once, right? Or we would have a perpetual motion machine, right?

Or something, right?

>Further to confuse the waters, I would assert that one of these revolutions is about its own axis, and one is not.<

I really, really should have more sense, shouldn't I? But I just cannot resist: OK PP, just how do you support that assertion??? Not with your glueing and unglueing surely? At all points in the original motion the "stationary wheel" was just that: stationary. Now suddenly you are moving it!  Foul, Ref!!!

If you are into that sort of thing, do you happen have titles for reference books that list all the fancy gear linkages one gets? I saw some beautiful ones with page after page of line drawings years ago, but lately I cannot seem to run any to earth on the web.

(Just hoping!)

Cheers,

Jon

You have to love this forum! The man with the funny avatar has done it again.

Paul's way of describing it might offend your sense of fair play, Jon, but you can't deny that the moving bob in your example describes two circles. The first is a revolution in a wheel-like manner; the second is a circuit in an orbital manner.

As for Mr Pedant's greengrocer's apostrophe (quote: two cent's worth) I can't resist pointing out that, there being two cents, his interjection is two cents' worth. Mind you, I don't want to set myself up as arbiter of usage of English because my own is distinctly imperfect. <smile>

>You have to love this forum! The man with the funny avatar has done it again.<

So what did you think I was winding him up for?

>... You can't deny that the moving bob in your example describes two circles. The first is a revolution in a wheel-like manner; the second is a circuit in an orbital manner.<

Yes and no. As you are well aware, though two circles are in fact described, your phraseology suggests sequence (no doubt inadvertently) but the two components you describe are not to be separated. Consider for example the situation when the rotating bob has travelled precisely halfway around the stationary bob; at that point the rotating bob is back in the same orientation as which it had started, but neither the "wheel-like" nor the "orbital" process has yet been completed; in fact each of them is still only halfway done.

Now, bewilderedly perched in the middle of the moving bob, my pet beetle has been monitoring events and has seen Betelgeuse describe two circles. Please tell me how to explain to him that one of these was due to a revolution in a wheel-like manner and the other an orbital manner.

Your move! :-)

>Your move! <

No no. Paul's move next. I'll just keep the pot bubbling if you two tire.

Actually, I deployed my two cents one cent at a time. First I spent one cent, and got one cent's worth. Then I borrowed another cent from an American sailor I met in a pub, and got another cent's worth. Then I put the results together and counted them, and they were then definitely two cent's worth.

I said "manifestly" because I got some coins out and did the experiment, starting with both coins in the obvious Queen's-head-vertical orientation (one Queen, two coins, no greengrocer's in sight), carefully observing the orientation of the moving coin throughout. "Manifest" means according to the evidence of one's own eyes.

All motion is relative. The coins were actually whizzing around the Earth's axis and the Sun and the Galaxy and all that good stuff. It seemed to me I could stand over the things and turn my head as I turned the outer coin (somewhat as in The Exorcist), and then turn it back at the end, and it would not materially affect the position of anything on the desk. And then I figured I could do what I wanted with the inner coin provided its start and end position were identical.

I would assert I am perfectly justified in decomposing the motion into separate parts, as I would in mechanics when solving a triangle of forces, or giving a map coordinate east then north.

Also, there is no reason that your Beetle should be able to gauge his motion by Betelgeuse. If it was directly overhead, he would have concluded he was not moving at all. If it was directly under his feet, he would have assumed it did not exist.

You're a bit of an entomologist Jon. You'd better become a coleopterist now.

Paul has lapsed into that strange version of English which I can't understand. Joshua?

You lads obviously missed out on part of your education. Maybe you spent too long on the Internet when you were teenagers. [Joke].

Paper Moon is a film about a depression-era Bible saleman and his estranged daughter, played by Ryan and Tatum O'Neill. Hence the stationary/stationery pun.

Incidentally, those used to be the same word anyway, but they drifted.

[[The word “stationery” however was originally spelled with an “a” in English. It derived from the fact that such products were sold in “stationary” shops and not from travelling peddlers. Both spelling derive from the Latin stationarius defined as a place where something is located.]]

Personally, I think the author of that article has spelled "spelled" wrongly - it should be spelt "spelt", unless I have miss-spelt it too. Damn, now I have mis-spelt mis-spelt as well.

While I was looking for that I ran across a blog concerning the history and fossils of ant-eaters. It's called Aardvarchaeology. Never mind.

Anyway, to Joshua, This is King James Bible (he lent me a copy), Book of Joshua, Ch 10, Verses 11-12, where we are engaged in kicking the wotsits out of the Amorites (presumably for being Amoral, or perhaps Amorous). God has already killed myriads of them with giant hailstones, in a pre-match punch-up. Now Joshua pleads to the great Ref in the sky for extra time because the light is fading.

"Then spake Joshua to the Lord in the day when the Lord delivered up the Amorites before the children of Israel, and he said in the sight of Israel, Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon."

"And the Sun stood still, and the Moon stayed, until the people had avenged themselves upon their enemies. Is this not written in the book of Jasher? So the Sun stood still in the midst of heaven, and hasted not to go down for a whole day."

I like the way that follows Wikipedia rules by referencing another independent source. It must be true, then.

Verse 20 mentions the first Concentration Camps, too. "... that the rest which remained of them entered into fenced cities."

While I was tracking down chapter and verse for Joshua, I ran across this assertion that NASA has a project to track down Joshua's missing day, because they believe it might happen again and put all their geosynchronous stuff out of position. Strangely, they have an animation where the Earth kind of catches in the track that keeps it in its orbit, and rolls around in contact with it for a while.

http://sunnyokanagan.com/joshua /index.html?gclid=CIjdwPjk5qYCFQJO4QodfGJT1A