[thedoc (OP)]

Shane Byrne  asked the Naked Scientists:
   Hi there  Dr Chris
Long time listener first time emailer :-)
OK so here is my question not sure where it would fit in but it has perplexed me for years and given your bent to make science entertaining I thought that my question would be perhaps of interest to others out there who are also scratching their head in perplexation ( a word I just made up).
When I pour a beer (hopefully you straight away see the necessity to try this yourself)
When I pour a beer from a can or bottle to the schooner glass that I stole from the pub down the road, I can't help but notice that the head goes all the way to the rim and almost over the top but seems to pull back just before it topples over (spills) down the side of the glass.
Now I am aware of the property of water (and perhaps other liquids) of surface tension that allows water at least to form a convex shape at the top of a glass. I am pretty sure this phenomena can't be that because of the bubbles which would break the surface tension.
Is it just that I am skilled at estimating the amount of liquid to pour into glasses so it doesn't spill or is it that as the beer reaches the top, then there is more surface area to 'dissipate' (not sure if this is the correct word here) the action of the head and so it slows down the 'growth of the head' so it doesn't spill.
I have tried this with other liquids in rare moments of sobriety - such as pepsi or coke and it seems to act in the same way.
Of course if I go way over the top with pouring then it does spill over, but am wondering if there are magical / mystical forces at play here. Perhaps the LIGO could be utilised to investigate this phenomena further. I'm sure it would be of interest to most of humanity.
Cheers
Shaby Sheik

 
What do you think?

[evan_au]

I am pretty sure this phenomena can't be that because of the bubbles which would break the surface tension.

Beer does have surface tension - and beers that have a good head will also have organics from the fermentation process which gives it a far higher surface tension than water.

Perhaps part of the process is that many beer glasses fan out towards the top. This means a greater area is exposed to the air; when these top bubbles pop, they reduce the height of the head. Where the glass is narrower, more of the bubbles are enclosed by other bubbles and the glass, so one bubble popping will just add to the volume of nearby bubbles, keeping a high column of foam.

Is it just that I am skilled at estimating the amount of liquid to pour into glasses so it doesn't spill

I am sure that many years of practice have honed your hand-eye coordination, so that you stop pouring at just the right time to avoid wasting one golden drop!

Perhaps the LIGO could be utilised to investigate this phenomena further.

Bubble chambers have been used for many years in subatomic physics - some of the early experiments apparently used beer as the working fluid. For this work, the inventor received the Nobel Prize for Physics in 1960. However, they have now moved on to more exotic fluids.