Why do glasses, cups and plates have a ridge around the base? Why not have a flat bottom?
If you imagine a plate with no ridge and there is some small piece of grit, food or dirt on the table the plate would rock and make it difficult to eat off it. However if you have a ridge it is very unlikely the grit is under the ridge itself and even if it is when you move the plate slightly the plate would fall off the grit becoming stable again.
It is also probably more difficult to manufacture a perfectly flat piece of pottery than a ridge that is the same height all the way around.
adrian asked the Naked Scientists: Hi Naked ones, Why do almost all the glasses, cups, plates you see have that edge at the bottom, rather than a flat surface? (Once I bought such a cup, with a flat bottom. It was a dangerous cup...). Regards, Adrian What do you think? adrian , Thu, 15th May 2008
With a flat bottom, they will slide around on a smooth table top if there is any water there - aquaplaning. The pressure under the ridge keeps good contact with the table - like the tread on tyres. lyner, Thu, 15th May 2008
:)This was a simple one:)
I cant say much about ceramics except I believe it helps in the firing process as Ceramics shrink when fired so it helps not to have the base completely in contact with the surface it stands on.
its to hold ur plate on the table and to prevent it from slipping while ur eating there is also another mechanism and it is that there is a vaccum created at the base of ur plate a low pressure vaccum and it basically holds ur plate on the surface. qazibasit, Sat, 14th Jun 2008
If you want a "flat" base, ie one that won't rock on a flat surface you have to grind the base of the thing flat. If the thing has a rim, you only need to grind that flat. Otherwise you need to grind the whole of the base flat.