Liquid Nitrogen Demonstration Movies
Thanks to Bill Kavanagh for filming and exporting these movies.
Magnetic Levitation
When cooled to low enough temperature, some materials undergo
a phase transition to the superconducting state in which they
can conduct electricity without any resistance. In this state,
they also expel magnetic field, a phenomenon known as the Meissner
effect. Until the mid 1980's the highest temperatures for which
superconducting temperatures were known were a few tens of degrees
above absolute zero (which is -273 degrees C). In the mid-1980's,
Bednorz and Mueuller discovered a family of ceramic materials with
with much higher superconducting transition temperatures. There are now
several ceramic superconducting materials with transition temperatures
the boiling point of liquid nitrogen (-196 degrees C).
Click here to download a web quality quicktime movie of magnetic levitation
above a disk of high temperature ceramic superconductor. The magnet
is lifted above the superconducting disk by the magnetic field
lines which are pushed out of the disk when it becomes superconducting.
SuperConductor(Web).mov.
Click here to download a higher quality quicktime movie of magnetic levitation
above a disk of high temperature ceramic superconductor.
SuperConductor(CdRom).mov.
Condensation of Air in a Balloon
When a given amount of liquid evaporates to a gas, it typically takes
up about 1000 times as much volume. Air is about 80% nitrogen
and 20% oxygen. If a balloon is cooled to liquid nitrogen temperature,
the air inside the balloon will condense to a liquid and take up
about 1/1000 of the space it filled as a gas. Because the material inside of
the balloon now takes up so much less space, the pressure of the
atmosphere outside of the balloon flattens it. The condensed air is
still inside the balloon and as it warms up, it evaporates and reinflates the
balloon.
Click here to download a web quality quicktime movie showing condensation of
the air in a balloon.
Balloon(Web).mov.
Click here to download a higher quality quicktime movie showing condensation of
the air in a balloon.
Balloon(CdRom).mov.
Freezing of a Rubber Hose
Rubber is a polymer. When rubber is relaxed, the long molecules of the
polymer are coiled up. When the rubber is stretched, the molecules
slide past each other and more or less line up along the direction
of the stretch. When a polymer is cooled to very low temperature,like
the boiling temperature of liquid nitrogen, parts of
the molecules in the rubber line up with each other so that they cannot
slide past each other. The rubber becomes very stiff and
brittle like a glass or crystal.
Click here to download a web quality quicktime movie showing the freezing of
a Rubber Hose in liquid nitrogen.
RubberHose(Web).mov.
Click here to download a higher quality quicktime movie showing the freezing of
a Rubber Hose in liquid nitrogen.
RubberHose(CdRom).mov.
Shrinking of Metal in Liquid Nitrogen
In all materials, the atoms move back and forth very rapidly.
When materials are cooled to very low temperature, the movements
of the atoms slow and become smaller. The space needed to accommodate
the movement of each atom gets smaller and the whole material shrinks slightly.
When building equipment to operate at low temperatures, this shrinkage
needs to be taken into account. The movie shows a brass ball and a brass ring.
At room temperature, the diameter of the ring is slightly larger than that
of the ball and the ball passes through the ring. When the ring is cooled
to the boiling point of liquid nitrogen (-196 degrees C), it shrinks so much
that the brass ball no longer passes through.
Click here to download a web quality quicktime movie showing the shrinking
of a Brass Ring in liquid nitrogen.
BallAndRing.mov.
Click here to download a higher quality quicktime movie showing the shrinking
of a Brass Ring in liquid nitrogen.
BallAndRing(CdRom).mov.