File talk:CardioidInCoffeeGlass.jpg

This appears to be a nephroid
The actual curve that appears depends on the shape of the cup and the angle of the light source. The most common case in practice is half of the nephroid, which occurs when the cup is a cylinder. When the cup is another shape then the curve that appears is more complicated. The shape of the cup is not given but the curve appears to be a nephroid since it loks like it's tangent to the edge of the cup at the top and the bottom. A cardioid appears in the the photograph here (or at least so the author claims) but in this case the cup is a more a bowl with conical shape and the light source is carefully positioned. The math of these curves is somewhat complex and I haven't seen a treatment of the three dimensional case which would tell you exactly which curve you get, even if you assume conical shape and not a more complicated surface of revolution.--RDBury (talk) 11:39, 25 September 2009 (UTC)