There must be a lot of studies of this, but they're probably all
classified! But the rapidity at which nucleation (the formation of
bubbles) can occur with the release of pressure on a supersaturated
mixture such as CO2 in pressurized water or in superheated water
itself is amazing.
BTW. Be careful reheating water in a microwave, if it's been heated
to the boiling point earlier without being disturbed in the interim.
In the first boiling, the nucleation sites on the surface of the cup
(say) may have been inactivated, so a simple shock will generate
nucleation sites in the bulk liquid and the boiling liquid will be
forcefully ejected from the vessel. That's probably why McDonalds
doesn't put microwaves out where the customers can use them? :)
Roger
On 5 Dec 2007, at 12:23 PM, Bob Blakely wrote:
Howdy!
The bullet traveling at high velocity through the air, or any
medium for that matter, has a vacuum behind it. If it's traveling
near or greater than the speed of sound, it also develops a shock
wave around it. The shock wave makes the bullet effectively larger
in diameter, and the vacuum behind it makes the bullet effectively
longer. At the speed of sound (~1100 ft/sec) the bullet with
surrounding shockwave and trailing vacuum goes from just outside
the can to just before exiting the can in about 200 microseconds
(0.0002 seconds). The bullet plus it's shockwave plus it's vacuum
is now displacing the fluid in the can nearly instaneously! The
fluid, unlike air, is incompressible and can't flow through the
bullet hole rapidly enough in such short period of time. The
pressure therefore rises (in this same 200 or so milliseconds) to
what would be near infinite save for the can bursting. This
pressure in the can propagates to every part of the can at the rate
of about 4800 ft/sec (approx. velocity of sound in water), so the
bursting pressure of the can is approximately the same around the
entire can. The bursting will take place first at the weakest
points of the can (usually at the seems), bullet holes and the
center of the longitudinal part of the can. With enough energy, the
can should turn nearly inside out.
The same thing happens when you shoot fruit, like apples or water
melons as they are mostly water. The whole thing bursts with extra
burst flow at both the entry and exit which can be seen using high
speed photography - speed usually provided by a fast strobe.
I shoot fruit all the time, as it's hyper velocity dart fun and the
exploded fruit is biodegradable, usually eaten as a feast by the
various denizens of the desert after I leave. A .270 rifle bullet
at Mach 4 hitting a water melon is quite impressive.
Regards,
Bob...
Engineer, firearms enthusiast.
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From: "ADavidhazy" <andpph@xxxxxxx>
Marilyn,
I am no physicist but I believe that once the bullet has entered the
can and it is pushing its way to the other side it displaces liquid
and this has to go somewhere and the only free space is the hole it
placed where it entered ... so backwards. Later on the second, exit,
hole appears and liquid is also able to go that way plus the bullet
drags some along as well probably.
In some way morbid this is related to the discussions about president
Kennedy's assassination.
Marilyn Dalrymple wrote:
Why is it the can blows out all the way around? I would think
that the side where the bullet goes in would sink in, the side
where the bullet leaves the can would go out. Is it due to the
"explosion" of the carbonated liquid in the can, or does the
bullet itself cause this?
