LIKE a ROLLING SODA
Materials:
- Two unopened cans of soda
- Inclined surface
Procedure:
1. Locate the inclined surface (If you’re experimenting at home, stick a book under a board, or prop up two legs of a table or something).
2. Teamwork required! One person stands at the raised end of the inclined surface with the soda. This person is the Roller. The other person stands at lower end of the inclined surface. This person is the Catcher.
3. The Roller should carefully lay the cans on their sides on the starting line (at the raised end of the inclined surface). When you’re sure the Catcher is ready, release both cans at the same time, and watch them roll. They should roll to the Catcher at about the same speed.
4. Return both cans to the Roller. The Roller should now select JUST ONE of the cans, and shake it vigorously for about 10 seconds. Repeat step 3 (Roll the cans to the Catcher again).
What’s Going On?
Wow! The unshaken can wins every time! This is because shaking the can knocks loose any bubbles sticking to the inner surface of the can. This causes the mass of the soda inside the can to be more evenly distributed throughout the can, causing it to roll more slowly. The unshaken can’s soda is (just a little tiny bit) more concentrated around the can’s axis of rotation (it’s center), and therefore rolls a little bit faster.
Think and talk about this!
There is a famous demonstration using a stool with a spinning seat. If you have one, you can try it. Spin on the stool with your arms held straight out. While spinning, pull your arms in tightly to your chest. Your spinning-speed will increase quickly!! It’s the same idea. The closer your mass is to your center, the faster you spin.
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