🚀 go-pugleaf

Steve Luzader has described an experiment of interest and a challenge for
those who are able to get their students to predict before the activity is
carried out.

 " Put a beaker of water on one side of a double pan balance and add masses
to
the other side until it's balanced.  Ask the students what will happen
if you put the end of your finger in the water but don't actually
touch any part of the beaker.  Will the pan with the beaker stay put,
move up, or move down when the end of your finger is in the water?  (I
leave the answer as an exercise for the reader.)"


One which we have tried is a practical investigation of Pirate Pete and the
good ship 'Archimedes'.  Most students like a good story and what better
than one about pirates.

Pirate Pete was going about his nefarious ways when he was challenged by
her Majesty's frigate Lollypop.  The Lollypop after putting a shot across
the bows(sharp end for non nautical persons !) of the Archimedes sent a
second shot into the side right on the waterline.  "Woe is me" said Pirate
Pete "I am done for the only way I can save my ship is to throw the gold
overboard and hence lighten my ship so that the hole is high out of the
water.  Besides being a very successful Pirate with lots of gold he also
undertsood cause and effect.

"No problem" said his faithful mate who had studied college physics under
very fine teachers. "Tie the gold to a rope and lower the gold overboard.
The ship will still float higher but you will not lose your gold and can
pull it up again after the hole is patched and the frigate has gone away."

Now we all can guess what happened or can we ?

In our lab we use a tall clear plastic container almost full of water in
which we place the good ship Archimedes.  Archimedes is a softdrink can
which has had the top removed and a small amount of plaster of Paris added
so that it floats upright.  The plaster is spread around the bottom so that
there is a hollow at the bottom of the can in which the gold can be placed
without upsetting the vertical balance of the can.  The gold is a plastic
film container filled with plaster until the lid will just fit back on
again.  The lid has a cuphook screwed into it.  Ship and gold should float
upright and the water level on the side of the container (and the side of
the vessel) can be marked easily with marker pen. The Archimedes has a
cuphook screwed into the bottom of it so that when the gold is removed from
inside the ship it can be hung under the boat and the boat and gold
re-inserted carefully into the water.  A small amount of silastic or other
material seals the cuphook into the can so that no water leaks into the can
through the bottom.

Question 1.     Does the ship float higher in the water or not ?

Question 2.     If the gold is allowed to fall off the ship to the bottom
                of the container will the water rise in the container, stay

                at exactly the same level or fall ? The use of a clear
                container allows the water level to be marked before and
                after the event so that any change can be observed.

Write down your expectations and reasons before doing it.  Any money gained
by betting on the results should be sent to a charity for old pirates.
David Bailey                              !  Faculty of Science &
Technology,
University of Western Sydney, Nepean            !  P.O. Box 10, KINGSWOOD  2747
Phone (047) 360 429  Fax (047) 360 713    !  Australia