Dancing Raisins!

20 07 2012

Now that it’s summer time, the extreme heat makes everyone want to go swimming! If you have gone swimming with a life vest before you know that life jackets keep you from sinking down into the water, but do you ever wonder how? This simple experiment can help explain.

Here’s what you’ll need:

  • a clear cup or glass
  • some raisins
  • club soda (make sure it isn’t flat!)

Instructions:

  1. First, open the club soda and pour it into the glass
  2. Then drop a few raisins into the cup of soda
  3. Wait about 20-30 seconds to see the raisin’s reaction!

What did you see?

The raisins should have dropped to the bottom at first, started floating to the top, and then fell back down to the bottom again. This should happen continuously for a few minutes! Take a look at how our experiment went:

Dancing Raisins! Buoyancy Experiment from Austin Children’s Museum on Vimeo.

The reason why the raisins dance in the club soda and then floats to the top is because the bubbles in the soda stick to the rough edges of the raisin making it more buoyant, meaning that it floats easily. The bubbles in the soda are carbon dioxide gas and help bring the raisins to the top, when the bubbles reach the top, they pop and release the carbon dioxide gas into the air. This makes the raisins fall back down again since it is denser than the liquid soda.  The bubbles make the raisins float to the top similar to how a life jacket keeps you above water!

The carbon dioxide gas bubbles popping at the surface

Bubbles attaching to the rough surface of the raisins

The bubbles lifting the raisins back up to the surface

Now that you’ve tried this simple experiment, try putting other small foods into the club soda to see how they react! Although not everything you try will float, it is always good to experiment! You could try peanuts, chocolate chips, apple seeds, or pieces of uncooked pasta to see how long it takes for the bubbles to bring it up to the top and how fast they move up and down in the soda. Let us know what results you got!

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