1. Hot Metal
If an iron torus (dounut / innertube shape) is heated uniformly, does the diameter of hole in the middle get bigger, smaller, or stay the same?
2. Bathtime Teaser
Little Jimmy is playing with a toy boat in the bath. It is floating in the water with a cargo of a wine cork and a metal bolt (Jimmy's family was not a rich one). Jimmy takes the cork out of the boat and is intrigued to see that it too floats in the water. He then takes the bolt out at watches it sink quickly to the bottom. Your problem is about what happens to the level of the bath water during Jimmy's experimenting. How does the water level at the beginning (cork and bolt in boat in bath), compared to that half way though (cork in bath, bolt in boat in bath), and that at the end (bolt and cork in bath, boat still floating in bath)?
3. Backwards and Forwards
Take a normal bicycle with stabilizers to keep it upright without being held. Now arrange the pedals so that the cranks are vertical, and tie a piece of string on to the lower pedal. If this string is now pulled backwards from the rear of the bicycle, which way does bike move?
4. In the Shadows
You are walking along pavement late at night, but luckily it is fitted with street-lamps at regular intervals. You are walking at a constant velocity and passing directly under each lamp. You notice that as you pass under a lamp, the end of your shadow starts off behind you, and then overtakes you as you walk. But what happens to it's velocity? Does it get faster, slower, or stay the same as you pass under the lamp?