I ran across the idea for this week's experiment (which is really more of a challenge), while researching another question. The more I thought about it, the more I liked it. It involves the unusual behavior of sand in a glass of water.
Have you ever played with water balloons? If so, you probably dropped one at some time, and got wet when it burst. What if it had bounced instead? Water balloons can be made to bounce very easily, if you know the science.
OK, a puzzle this time. Imagine that you have two steel bars that look alike. One is a magnet and the other is not. Without using anything else (No paperclips, iron filings, etc.) how would you be able to tell which is the magnet?