Dancing Raisins - The Bubble Lifter Chemistry you can eat! email to friend
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1. Fill the glass with soda.
2. Drop 10-15 raisins into the soda.
3. Focus all of your attention on those raisins.  Are they moving?  Yes!  They’re floating, they’re bobbing up and down, they’re dancing!  OK, maybe it has something to do with those bubbles attached to the surface of the raisins.  Watch closely as you read the explanation.

Dancing Raisins Variation

1. Set up your drinking glasses with different types of soda.
2. See which type of soda makes the best dancing raisins.
3. Try using all of the same type of soda but different kinds of "dancers."
4. Throw in corn, macaroni, noodles, lentils, craisins, even corn!
5. Which combination of soda and dancers "performs" the best show?
6. Keep experimenting until you find the best combination!

How does it work?

You can guess why this is an extremely popular activity among elementary teachers.  With each rise and fall of the dancing raisins a new chorus of ooohs and ahhhhs erupt from the students.

The raisins will bob up and down for several minutes.  This “raisin dance” is captivating to watch.  Since the surface of the raisins is so rough, tiny bubbles of CO2 will be attracted to it.  These bubbles will increase the volume of the raisin substantially, but contribute very little to its mass.  As a result, the overall density of the raisin is lowered, causing it to be carried upward by the more dense fluid surrounding it.
                                                                   
Archimedes’ Principle states that the buoyant force exerted on a fluid is equal to the weight of fluid displaced.  Since the raisins now have a greater volume, they displace more water, causing the fluid to exert a greater
buoyant force.  The buoyant force of the surrounding fluid is what pushes the raisins to the top.

Once the raisins reach the top, the bubbles pop upon exposure to the air.  This makes the raisins more dense, causing them to sink.  As more bubbles adhere to the raisins, they again become less dense and are pushed back up by the fluid. This experiment very clearly shows that an increase in volume (as long as
the mass increase is negligible) will lead to a decrease in density.  The bubbles that attach themselves to the raisins can be thought of as little life jackets that make the raisins more buoyant by increasing their volume.

If the raisins are added directly to the bottle, replace the cap on the bottle after they have made several cycles.  After a few minutes, all of the raisins will rest at the bottom. This is because carbon dioxide gas is
prevented from leaving the bottle.  As a result, pressure builds up in the space above the fluid.  This pressure is transmitted throughout the fluid, and the bubbles cannot grow as large.  Therefore, the volume of the raisins does not increase enough to lower their density to the point where they are less dense than the fluid.  When the cap is removed, the pressure above the raisins is decreased, allowing the bubbles to grow larger, causing the raisins to resume the cycle of their “dance.”

You can see the same thing happening with set of inflated Water Wings™ or an inner tube.  The volume of the Water Wings increases the person’s volume considerably.  However, the mass of the Water Wings is very small.  The overall effect is to lower the density of the Water-Wings-person combo to less than that of water, so that the person can float.  Deflating (don’t try this with someone who can’t swim!) the Water Wings would reverse the process and cause the person to sink.