Incompressibility of Water
properties of water - liquids - incompressible fluids
What it shows:
Water is so incompressible - one part in 5×107 decrease in volume for
each atmosphere increase in pressure - that it is incredibly rigid if constrained within a solid skin.
Even a glass flask can turn into an excellent hammer!
How it works:
Instead of a thin walled glass flask hitting a nail in which a slight deformation at the impact point
is easy and catastrophic, the flask is effectively a solid mass; the water preventing the glass
surface from deforming. The liquid core also has the ability to distribute the shock isotropically
throughout the sphere, allowing the entire surface for the glass to absorb the impact.
Setting it up:
Use a 1 liter round bottom flask (obtained from your friendly chemistry department), and fill - we
mean FILL; no air bubbles can be permitted to form when the flask is sealed - with distilled water.
To do this well, boil the distilled water for a while to drive out the dissolved air and let it come back
to room temperature before filling the flask. Even better, pump on a flask of room temperature
water using a filter pump or aspirator while the flask is submerged in an ultrasonic cleaning bath,
until no more bubbles appear. It's amazing how much air there is in water, and air is compressible!
Seal with a rubber stopper and silicon rubber sealant. Electrician's (plastic) tape can be used to insure
that the rubber stopper remains in place. With this glass hammer you can strike a nail into a piece of
wood using reasonable force.
For the target, use a short piece of 2×4 with a large flat head nail already knocked
some way in so that it stands freely. Precautions are in Comments.
Comments:
When using this tool, ensure that you hit the nail square on the head - a side impact could mean
an early bath. Wear goggles and gloves. Also don't get carried away; below the soft 2×4
is a very hard lecture bench. Rating ***