Experimenting with a bowl full of hot soup is likely to be messy. We propose that we can substitute a circular carpenter's level. Sitting on the table, the bubble is at the center; when you bump it, the bubble goes off center. If the bubble goes all the way to the edge, you have spilled the soup.
1. Observe how motion affects a bubble level.
While keeping it flat on the table top, make it speed up, slow down,
go straight, turn corners -- any motion that you want to explore.
Move it slowly enough so that you can always observe the bubble.
2. Place two pieces of tape about a half-meter apart at the end of your table. Pretend that the level is a bowl of soup. You want to move it from one tape marker to the other, but the bubble must never touch the edge of the level (because that would mean the soup spilled!). The level starts at rest (at a stand-still) and ends at rest. Explain how to move the level as fast as possible without "spilling the soup."
3. Practice sliding the level on its card in a straight line at constant velocity. What does the bubble do while the level is moving at constant velocity?
4. Which way does the bubble go while you are pushing on the level to make it start moving?
5. Move the level in a straight line at constant velocity. Then let it come up against your other hand to make it stop moving. Which way does the bubble go at the instant that it comes up against your hand?
6. Place a marker (a piece of paper, or a sticky note) on the table, and move the level around the marker in a circle. What does the bubble do? Observe the cases that the motion is slow or fast, and that the circle is small (10 cm radius) or larger (30 cm radius).
7. Think about all the observations you have made with the level. What does the bubble tell you about the motion of the level? How is this related to how you are pushing on it?
Check the box when you are done: