Floating and sinking octopus

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Materials required: dropper, large nut (M6), small nut (M5), zip tie, red water balloon, air pump, plastic bag, wide-mouth plastic bottle
• First, make a Cartesian diver.
• Fill a wide-mouth plastic bottle with water, and fill the water balloon. If there is air in the balloon, then let it out.
• After filling the balloon with water, then fix the mouth with a zip tie. Cut out the legs from a red-painted plastic bag, wrap them around the Cartesian diver, and fix them with a zip tie to complete.
• Adjust the amount of air in the dropper, fill a wide-mouth plastic bottle with water (work in a bucket filled with water), and close the lid. The top and bottom of the octopus are upside down, so use the plastic bottle upside down.
• If you push the side of the plastic bottle with your hand, the octopus will sink, and if you do not push as hard, then it will float.
  (If it does not move easily, then adjust the amount of air in the dropper, or try covering the mouth of the plastic bottle with a balloon and stopping it with rubber, just like we did with the Floating and sinking squid)
• Pressing the plastic bottle increases the pressure of the water and air inside it. The air in the dropper is compressed, and its volume decreases, reducing buoyancy and causing the object to sink. Conversely, if you do not press the bottle as hard, the air expands, buoyancy increases, and the object floats.

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

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