Thursday, July 10, 2014

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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  1. Ooh, very scientific, but the ketchup sachets remind me of when my little one was 5. He stashed a couple of them in his pocket just in case we got lost and had to slug it out in the wild!

  2. What a neat experiment. Will have to try it the next time I get a ketchup sachet.

  3. I did this with the boys a while ago and they were fascinated by it - older lad worked out how it worked too :) Popping by from France via UBC

    1. Eco Gites of Lenault, it is great that your boys enjoy the experiment!

  4. So cute, must have been total fun for them. Love the way they are engrossed to the bottle.

  5. Very scientific indeed!
    What great fun!

    1. For older children, this experiment is used to explain more science concepts.


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