杏吧原创

Beer buoys

Question: I recently held a barbecue, and to help the party along I filled a
plastic dustbin with ice and cans of beer. When the ice melted, the remaining
cans were left floating at all angles in the water. By the following morning,
however, all were floating vertically鈥攅xcept for those containing widgets,
which remained either disoriented or had dived to the bottom of the dustbin.
What is going on here?

Answer: It鈥檚 all to do with gas. The reason the beer cans align vertically
overnight and float is because, by the morning, they contain more carbon dioxide
in the form of gas.

While the cans are immersed in ice or icy water, the CO₂ contained
in the beer remains dissolved. However, as the ice melts and the beer鈥檚
temperature rises, the CO₂ begins to form bubbles as it returns to a
gaseous state. As more bubbles form they begin to aggregate and a slight
disturbance to a floating can will cause the aggregated bubble to shift
preferentially to the higher end of the can rather than sit precariously along
an inside edge.

You will probably find that the end at the water鈥檚 surface is the one without
the ring pull. The ring pull end of the can is heavier and more likely to
sink.

The reason cans with widgets remain in their original positions is that there
is no CO₂ dissolved in the beer. Instead, the gas in these cans is
nitrogen contained inside a tiny device that only releases it when the pressure
in the can falls after opening. Any increase in beer temperature will have no
effect on the amount of gas already present in the can.

Dave Hooson

Huddersfield, West Yorkshire

Answer: Some of the floating widget cans may have sunk to the bottom the
following morning because the density of the water had changed. Water has its
maximum density at about 4 掳C. Liquids of high density are better able to
support floating objects. That is why people float so easily in the dense Dead
Sea. Therefore, the water was able to support some of the cans at low
temperatures but by the next morning the water had warmed up and was unable to
support the cans because of its lower density.

Simon Iveson

Mayfield, New South Wales

Answer: Your correspondent鈥檚 question about floating cans begs another of
greater import. Why were there cans of beer left over at all? There鈥檚 a
vanishingly small chance that this phenomenon would have been allowed at an
Australian barbie.

Peter Miller

Sydney

Out of your skull

Question: If your eyes were popped out of your head, turned upside down and
placed back in their sockets would you see the world upside down?

Answer: Ghastly as this procedure seems, it would leave you looking at the
world upside down, if it hadn鈥檛 already caused blindness due to damage to the
nerves and muscles surrounding the eye.

If you ignore physical damage and treat the eyeballs as a unit, leaving each
only attached by the optic nerve, the retina as part of the eyeball itself would
be inverted, and the effect would be similar to what one sees while standing on
one鈥檚 head.

However, one difference to note is that your eyes would also be reversed.
When you stand on your head, your left eye is where your right normally is, and
vice versa, but if your eyes were screwed in upside down, the left one remains
on the left. This would lead to quite interesting problems with depth perception
until the brain adjusted.

Many people have shown that the brain is able to adjust quite quickly to
altered visual inputs. In one particular experiment, Steve Mann at the
University of Toronto used a system consisting of cameras and displays covering
his eyes to show the world at right angles to normal, and was able to adjust in
a matter of days.

A much easier way to duplicate removing your eyeballs is to investigate
artificial systems such as wearable computers, constructed from old video
camcorders, which allow remapping of the visual inputs. Then you can play with
your senses without the pain and damage of surgery!

Alex Feinman

Waltham, Massachusetts

Answer: If you see the world inverted for long enough, your visual field will
eventually flip over to correct itself.

In 1897, George Stratton, a Californian psychologist, wore goggles that
turned his world upside down. He reported that, after some initial
disorientation, he was able to ride a bicycle a few days later. In the late
1950s, Ivo Kohler, an Austrian, tried this and discovered that he too could
adjust to an upside-down world.

More recently, Kaoru Sekiyama, a psychologist at Future University in
Hakodate, Japan, persuaded four students to wear left-right reversing goggles.
They were uncomfortable for about a week, suffering dizziness and even vomiting.
Over the first 10 days, they slept more than usual but, after a month, they were
also able to ride bicycles.

Stuart Anstis, a cognitive scientist at the University of California, has
even used a video camera to live in a photographic-negative world for three
days. He found it disturbing and confusing but he eventually adapted.

When the distorting goggles used in these experiments are removed, the
unpleasant readjustment process is typically much faster than the initial
adaptation. Jim Matiya of the Carl Sandburg High School in Illinois makes sets
of inverting goggles, left-right goggles, or displacement goggles. You can see
his colleague wearing a pair on www.d230.org/cs/matiya/.

David Lorde

Faversham, Kent

Answer: Experiments of this type have often been carried out, starting with
Stratton鈥檚 鈥淪ome preliminary experiments on vision鈥�, printed in
Psychological Review. However, it is not necessary to physically reverse
the eyes. Usually prisms are used for reversal, but some studies use video
cameras.

Subjects feel seasick initially, caused by conflict between vision and
balance senses, but after a few hours can walk as well as they can when they
have their eyes closed. After about two weeks they can touch indicated objects
quickly, although they make errors when asked if an object is to the left or
right of another. After a month they have almost fully adapted and can catch
balls, ride bicycles and function well.

After the spectacles are removed they have to adapt back to normal vision but
this occurs much faster. Interestingly, they re-adapt to the reversed glasses
more quickly a second time.

Brian Horton

West Launceston, Tasmania

This week鈥檚 question

Peat ponds: While walking in Scotland鈥檚 Cairngorm mountains, in an area where
there are thick deposits of peat, I noticed that many stagnant ponds seemed to
be covered by a film that displayed the same swirling patterns of rainbow
colours seen when oil floats on water. Do hydrocarbons form in the peat or is
there another explanation?

Michael Ghirelli

Hillesden, Buckingham