Nautilus in a Bottle – Potty Science Club

Hello and welcome to Potty Science Club session number 6!

All our experiments are conducted in a home environment, not in a lab, and will be safe and simple using equipment and items you can find in your own home. The experiments will reflect on an item or exhibit held in the Museum’s collections. Today’s experiment involves using scissors, which may require adult supervision or assistance.

A special item amongst the museums many collections is the wonderful shell of a Nautilus. The Nautilus is a member of a group of animals called cephalopods (meaning head-foot). these special creatures have hard external shells and are relatives of the now extinct Ammonites and Belemnites and the living Octopuses and Squid.  Cephalopods originated in the Late Cambrian Period 570 to 500 million years ago but the Nautilus is the only cephalopod with an external shell still alive today.  These amazing creatures first appeared about 500 million years ago and there were many different species living in the seas throughout the ancient world.

Unfortunately, today there are only a few surviving species of the Nautilus. These are found in the seas around Australia and the Philippines. Nautiluses have changed very little over the millions of years they have been around. The Nautilus lives in its shell with only its head and tentacles outside and the shell is divided into chambers filled with gas.  It’s by adjusting the levels of gas that the living Nautilus and can move up from the depths of the ocean to the shallow waters at night time to feed. The gas contained in the Nautiluses chambers is slightly below atmospheric air pressure at sea level.

In this experiment, we will be able see how air pressure can be demonstrated using a water bottle and float. You will also be able to control the float inside the water by altering the air pressure. 
For this experiment you will need:

                                     

A straw (I use re-useable or recyclable straws)
Plasticine, Play dough or similar (I used Blutac)
An empty plastic 2L bottle
A measuring jug
and Scissors

First, cut a small length of the straw. Then plug one end of the straw with plasticine or Bluetac. On the opposite end of the straw, make a ring of plasticine around the outside of the straw. so the straw is weighted but is open at that end). Pop it into the jug of water with the weight at the bottom to see if it floats with just the tip at the surface.  Adjust the weight of the float, adding or removing plasticine until it floats correctly. Keep trying until you get it right.

Next, fill the bottle three quarters full with water. Drop the straw into the bottle weighed-end down (to trap air in the straw) and put on the top, making sure it’s nice and tight. Squeeze the bottle as hard as you can and watch what happens……

The straw will sink!

Take a look at the video to see how I do it:

So what’s going on in the bottle?  

Water and air in a closed bottle create a sealed pressure environment. The air trapped inside the straw makes it float. When you squeeze the bottle you compress the space inside, making less space for the air to circulate, so the air pressure inside the bottle increases, pushing water up into the straw. This makes the straw heavier, so it sinks. When you release the pressure on the bottle, the air has more space to move again, so the pressure decreases and air fills the straw, making it float back to the top of the bottle.

You are watching air pressure in action.  Amazing don’t you think?

By Rob Gagliano, Casual Learning Development Leader and Natural Science Collections Volunteer

Written by museumvolunteers - Modified by Glenn Roadley (Curator, Natural Sciences)

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