Floating and sinking squid

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Experimental procedure and explanation:

• Materials required: dropper, large nut (M6), small nut (M5), zip tie, empty mayonnaise container (50 g capacity), plastic bag, thick plastic sheet (1–2 mm thick), rubber balloon, thick rubber band, wide-mouth plastic bottle, Scotch tape
• Stick the dropper through the large and small nuts and fix them with a zip tie. Cut off the excess with scissors.
• Cut 10 legs out from a plastic bag, wrap them around the dropper, and temporarily secure them with Scotch tape.
• Fix the wrapped vinyl sheets with a zip tie. The Cartesian diver is complete.
• Cut of the top and bottom of the empty mayonnaise container and staple a thick plastic sheet cut into a triangular shape to the top. (Can be painted with white spray paint)
• Insert the Cartesian diver into the body and staple both sides.
• Float this on water and adjust the amount of air in the dropper such that the tip of the head floats slightly out of the water.
• Fill the wide-mouth plastic bottle with water and add the squid.
• Cut off the mouth of the rubber balloon, put it over the mouth of the wide-mouth plastic bottle, and secure it with a thick rubber band. At this time, work in a bucket filled with water to prevent the entering of air.
• Press the rubber membrane of the mouth with a ping-pong ball or something round. Then, the squid will sink, and if you do not press very hard, it will float up (if you do not have a ping-pong ball, you can press with the palm of your hand).
• When you press on the mouth of the plastic bottle, the pressure of the water and air inside the bottle increases. This causes the air to compress and its volume to decrease, reducing the overall buoyancy and causing the object to sink. Conversely, if you do not press as hard, the air expands, increasing the buoyancy and causing the object to float.

[Keywords]	Pressure, buoyancy
[Related items]	Cartesian diver, Floating and sinking jellyfish
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, p. 42–47.

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