Dunno if this is the right place for this but...

[GirGirl]

Can anyone please tell me why Manhole covers are round?
i can't see how this could improve their function in any way...

Fanks in advance.

x

[Tim Baxter]

Well Tommy, possibly the best bit of B*llsh*t I've seen for ages, almost all your assertions are wrong and to back them up by misquoting from the Mint is beyond belief!  See the correct quote below.

While this design may have been traditional, the shape of the new 50p coin, an equilateral curve heptagon, was revolutionary. This made it easily distinguishable from round coins both by feel and by sight, while its constant breadth allowed it to roll in vending machines

If you stand one of the coins on its edge and gently try to displace it it will roll back to its original position.  This means that it is in stable equilibrium and its centre of gravity is at its lowest point.  If you try to displace it, it raises its centre of gravity (gets further away from its resting surface) and rolls back to its lowest point.  This disproves any 'constant diameter' theory (even though the mint claims it too!)

Any comments?

[tommy_g003]

Yeh i can think of quite a few comments, but i won't list them all.

Firstly, I didnt quote the mint. If I had done, I would have used quotation marks.

Secondly, it *is* an equilateral curve. This assertion is correct, google it. Here's a quote from an online encyclopedia: "The sides are not straight but are curved so that the centre of curvature is the opposite apex of the coin - this is an equilateral curve which allows the coin to roll freely in slot machines." 'Roll freely' means 'roll without getting jammed', not 'roll as easily as a circle'.

Thirdly, your explanation may contain long words and the 'centre-of-gravity', but if you'll take the time to roll a flat object along on a 20p or a 50p, you'll see that the object does not rise or fall in the slightest. You couldnt tell it from rolling on a circle. This shows it has a constant rolling diameter, and ANY READER can try this for themselves.

Fourthly, you mentioned the 'stable equilibrium' of the coins. I agree that this would make it harder to roll smoothly but think about it, vending machines must measure the diameter of coins as well as their weight, otherwise you could put a small lead pellet in and pass it off as a pound. The 'constant breadth', or diameter, means a machine can distinguish coins reliably using slots of different heights. Your static-analysis-for-beginners DOES NOT disprove anything to do with the constant diameter, which you can show is true in the manner described above.


Tim, you're not as clever as you think you are, but if it's any consolation, you're probably far cleverer than people that have met you give you credit for.

- Tommy G