critical thinking

920

Ice in bird bath
We are expecting a hard freeze tonight. The water in our bird baths will probably have a layer of ice, if they don't freeze solid. If cold water sinks, why does the ice form at the top?

924

Trees with yellow leaves
Although we have had several freezes, the leaves here are just starting to change. Every year, the leaves start changing colors in the North first, and then the color change spreads South. This is not due to the temperature. What causes it?

926

Running horse
Running horses played an important role in the development of a very common, modern technology. What is it?

940

Magnets
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?

944

Ball on paper plate
If I roll the ball around the paper plate in the direction of the blue arrow, when it gets to the place where I cut out part of the plate, which path will it take? A, B or C? Why?

Pages