force and interactions

Hanging a Hammer

This experiment involves balancing a hammer, a ruler, and some string. It is one of those balancing tricks that seem as though they just should not work, even though you understand the science behind them. I first learned it when I was eight years old, but it is still one of my favorites.


These are ripple marks in beach sand, made by the wind. Similar ripples can be seen in deserts, and even in large playground sandboxes. What causes the ripples to be so evenly spaced?


I took this photo at the beach. Looking at the tire tracks made me think about why car tires have treads, instead of being smooth, like racing tires. Why?


This photo is downriver from the dam on the Colorado River at Page, Arizona. Both the dam and the bridge support are curved. Why?


Kingman, Arizona has many faults, and this is one of them. Faults are places where pressure has caused the rocks to break and move. The way the rocks break can tell us about that pressure. Was this fault caused by pressures pushing the rocks together or pulling them apart?

Sail Fans

I got the idea for this experiment while driving around town. We were driving across the Bridge of Lions in St. Augustine, and I pointed out a sailboat that had a large fan-like propeller sticking up behind the sail. The propeller is attached to a generator, using the wind to recharge the batteries. We joked about it being a fan to provide wind if the breeze died down, which lead to a discussion about what would happen if you tried that. That lead to this experiment.

To find out what would happen if you did mount a big fan to blow on the sails, you will need: