Why is foam made in liquid?

Question

Sometimes there is white foam around the rim of the glass, and I'm wondering why it does that.

Answer 1

gasses that are lighter than the liquid will escape.  They come to the surface in the form of tiny tiny bubbles (that's what foam is-tiny tiny bubbles).  The bubbles reach the surface but haven't yet exerted enough pressure to get all the way out of the liquid.  There is surface tension from the gas inside and as it gets greater (gravity works, pulls the liquid down), most of the time the bubble bursts.  Sometimes it never reaches that point and you end up with that foam on the surface of the glass.  Near as I can figure.

Answer 2

WIth as much information as you have given you could possibly not be rinsing your glasses well enough after soaping them up.

Answer 3

Need more info, what liquid are you speaking of?