Ketchup Sachet Submarine - Cartesian Diver Experiment

"It is floating! Now it sinks! And it floats again!" The children exclaimed in excitement.

The cause of excitation? A packet of ketchup sachet in a bottle of water!

How to control the floating and sinking of the ketchup sachet in the bottle of water?

Just press the bottle, the ketchup sachet sinks. Release the bottle, the ketchup sachet floats!

Some tips for conducting this science experiment:

• Completely fill the bottle with water up to the brim
• Choose a water bottle that is not too hard to press
• Before inserting the ketchup sachet, conduct a pre-test: put it in a bowl of water, use the sachet that floats. Oh, we tried using ketchup sachets from different fast food restaurants, only the one that you see in the photo above can float 

How does it work?

When you press the bottle, while the water cannot be compressed, the air bubble in the ketchup sachet is compressed. The volume of the ketchup sachet decreases, and hence its density increases (density = mass / volume), and is greater than the density of water, so it sinks! 

For Pei Pei and Hao Hao, they are still too young to understand the concept of density, so this experiment was just for them to understand the idea of floating and sinking.

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