This is an experiment you will not want to miss trying out with your kids! 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!
What you’ll need:
– Clear cup or glass
– Club soda (make sure it isn’t flat) or Sprite
1. Open the club soda or Sprite and pour it into the glass
2. Drop a few raisins into the cup of soda
3. Wait about 20-30 seconds to see the raisin’s reaction!
To make it interesting, first ask your child what they think will happen to the raisins once they have been dropped into the club soda. Record what their hypothesis is and make observations for what is actually happening. Ask questions as you continue along with the experiment:
- What happened when you first dropped the raisins in the glass?
- Why did they sink?
- Once they started “dancing” did the raisins stay at the top?
- What else did you notice happening to the raisins? Did they look different?
- Do you think the same thing would have happened if you put raisins in water?
- What other objects do you think would “dance” in soda?
Take a look at how these experiments below went:
What’s going on?
As you and your child observed the raisins, you should have noticed that they initially sank to the bottom of the glass. That’s due to their density, but because raisins have a rough, dented surface, they are filled with air pockets. These air pockets attract the carbon dioxide gas in the liquid, creating the little bubbles you should have observed on the surface of the raisins.
The carbon dioxide bubbles increase the volume of each raisin without raising its mass. When the volume increases and the mass does not, the density of the raisin is lowered, allowing it to be pushed upward by the surrounding fluid, which now has a higher density than the raisin.
These bubbles increase the volume of the raisin substantially, but contribute very little to its mass. With a greater volume, the raisin displaces more fluid, which then applies more buoyant force, pushing the raisins upwards. (This is Archimedes’ Principle of buoyancy at work).
At the surface, the carbon dioxide bubbles pop and the raisins’ density changes again. That’s why they sink again. The whole process is repeated, making it look as though the raisins are dancing.
Extend the learning:
Now that you’ve tried this experiment, try putting other foods into the soda to see how those foods react! Not everything will float but it doesn’t hurt to play around and experiment. Try putting the raisins in a jar that has a replaceable lid or directly into a bottle of soda. What happens to the raisins when you put the lid or cap back on? What happens when you take it back off? Try foods such as peanuts, seeds, chocolate chips or pieces of small uncooked pasta to see what happens… do they float or sink?