Message-Id: <v01540b2faedf81de8a38@[192.174.2.173]>
Date: Thu, 19 Dec 1996 15:54:24 -0800
To: pinhole@exploratorium.edu
From: pauld@exploratorium.edu (Paul Doherty)
Subject: racquet balls in liquid n2
Warning
In the latest Physics Teacher a demonstration is described briefly as
"Racquet Ball in liquid Nitrogen"
I discovered that this activity can be dangerous.
In the first non-dangerous version I put the racquet ball into liquid
nitrogen and left it there only for a minute, until the vigourous boiling
stopped. I then used tongs to remove the racquet ball and dropped it onto
the ground where it broke in half. Satisfyingly showing that some materials
become brittle when cooled.
In the second, dangerous, version I left the racquet ball in the liquid
nitrogen for 30 minutes.
When it was removed from the liquid nitrogen and dropped on the ground
there was a loud boom and flying sharp shrapnel-like pieces of racquetball.
(I was wearing eye protection!)
Can you figure out why this happened?
scroll down for my analysis.
When the racquetball is left in the liquid nitrogen for a long time the air
in the raquetball liquifies creating a vacuum inside the racquetball. The
racquetball maintains its shape because it is solid and stiff. When it
fractures however an implosion happens, the racquetball is broken into
rapidly moving pieces.
Paul Doherty