Science Buddies: "Ask an Expert"

So, I'm working on a project based on "The Power of Heat is Right Under Your Feet", and I can't figure out a positive and negative control. Instead of 1 can, I'm using 3 different ones, and also at 60 seconds above the cans instead of 20. I'll measure the rpm above the cans at 1, 2, and 3 inches then average it for the results. Any advice on what I could do for a positive and negative control?

Hi tamurai,

Not all experiments have positive and negative controls. This project falls into that category - it doesn't have clear-cut positive and negative controls. The closest thing would be to consider a situation in which the pinwheel should definitely spin (positive control) and a situation in which the pinwheel definitely should not spin (negative control). That way you will know that the pinwheel is working correctly.

For example, the closest thing to a positive control would be to hold the pinwheel in front of a fan. Ideally, the pinwheel should spin because air is blowing past the pinwheel.

A negative control would be to hold the pinwheel above the hole in the foil without any steam coming out and measuring how fast the pinwheel spins with no steam coming out of the hole. Ideally, the pinwheel shouldn't spin at all because there is no steam coming out of the hole. (The steam is associated with a stream of air moving out of the hole.)

Post back if you have other questions.