Key concepts
Energy
Power
Forces
Machines

Introduction
Have you ever ridden your bike into a strong wind? If so, did it feel really tough? How does this compare with how you feel when the wind is pushing against your back? Does that make you feel ready for the Tour de France? In this science activity you will explore how wind-powered devices, such as wind turbines and pinwheels, also react in different ways to wind direction.

Background
Wind turbines are machines that change the energy in wind into mechanical or electrical energy. Windmills are examples of wind turbines that convert wind energy into mechanical energy. The Netherlands is a country well known for its windmills that have been used for centuries to grind corn, drain land and cut wood. Wind farms, on the other hand, are examples of wind turbines that convert wind energy into electrical energy. In California you can see rows of wind turbines along windy ridges and mountain passes. The wind turbines on these wind farms connect directly into power grids and produce 5 percent of the electricity that that entire state uses.

A wind turbine has a rotor with blades that is connected to a shaft. As wind energy hits the blades, the rotor turns, which causes the shaft to turn as well. As the shaft turns, it is able to do work and produce either mechanical or electrical energy. The more wind that hits the blades, the more the rotor can turn and the more energy the wind turbine can produce.

Materials

• Pinwheel (If you do not have a pinwheel, you can make a homemade one using a sheet of paper, a pencil or pen, a round wooden skewer and scissors—see steps below.)
• Hair dryer (optional)

Preparation
• If you do not have a pinwheel, make one now by going through the following steps.
• Cut a sheet of paper so that it is a square (8.5 inches by 8.5 inches is ideal).
• Fold the square of paper along the diagonal, then unfold it back into a square again. Fold it along the other diagonal, and then unfold it once again. Your paper should now look like a square with a big "X" made by the creases.
• About two inches out from the center, along each crease, make a small mark with a pen or pencil.
• Carefully make four holes with a skewer to the right of each crease near the square's corners (for more details see the pattern shown here in figure 3) and a hole in the paper's center.
• From each corner of the square, cut down along the crease until you reach the mark you made.
• Lastly, pick up each of the holes at the corners and fold them, one at a time, over onto the skewer, so that they are all on top of one another. You should now have a functional, homemade pinwheel!

Procedure
• If you want, you can use a hair dryer to blow on the blades instead of blowing on them yourself. If you do this, keep the hair dryer on a low setting and be sure it is about the same distance from the blades each time you blow on them.
• Face the front of your pinwheel and blow directly at it. Imagine that the pinwheel is a wind turbine, and when it spins in this direction it is turning the energy of the wind into electrical energy. Which way do the blades spin, clockwise or counterclockwise? How fast do they turn?
• Turn the pinwheel so that its front side is now pointing to your right. You should now be facing the side of the blades that were previously on your left. Blow on the top half of the blades, above the shaft that goes through the blades. Try to blow similarly (with a similar force and distance) as you did before. Which way do the blades spin, clockwise or counterclockwise? How fast do they turn? How does it compare with blowing on the front of the pinwheel?
• Still facing this side of the blades, blow on the bottom half of the blades, below the shaft. Try to blow similarly to the way you did before. Which way, and how quickly, do the blades spin now? How does this compare with blowing at the pinwheel from the other directions?
• Now turn the pinwheel so that its front side is pointing to your left and you are facing the opposite side of the blades. Blow on the top half of the blades, similarly to how you blew on them before. Then blow on the bottom half of the blades. Which way and how quickly do the blades spin each time?
• Overall, how does the direction of the wind hitting the pinwheel affect how the blades spin? If the pinwheel were a wind turbine and blowing on the front of it generated electrical energy, which direction(s) should it receive wind from to efficiently make electrical energy?
• Extra: Try repeating this activity with a few different pinwheels. Do you get the same results for each one?
• Extra: If you want a more challenging activity, you can try to quantify how much power the pinwheel makes when it is blown on from one direction compared with another direction. To do this, you will need to attach the pinwheel blades to a fixed shaft (for example, a wooden skewer) so that they rotate the shaft when they are blown on. Support the shaft by putting it through a cardboard oatmeal canister or similar object. On the other end of the shaft, tie a piece of thread with small weights (for example, paper clips) on it. When the pinwheel is blown on and the shaft turns, it should pull up the weights. For more details on how to create this setup, see the Science Buddies project idea in the "More to explore" section. How much mechanical power do you think your pinwheel can produce?

Observations and results
When you blew straight onto the front of the pinwheel did it spin counterclockwise? Did it spin best when you were blowing into its "cups"?

Most pinwheels have the blades arranged so that when wind blows straight at them, they spin counterclockwise. This is because the blades' "cups" are made so that the oncoming air is captured and pushes the blades in this direction. (You can try looking at several different pinwheels to see this pattern shared among them.) When wind is blown into the cups, the pinwheel spins well. Consequently, if you are using a typical pinwheel, turn it so that the front side is facing your right and blow into the side of the blades. The blades will spin quickly counterclockwise if you blow on the bottom half (into the cups) but will spin slowly clockwise if you blow on the top half (against the backs of the cups). Similarly, if the pinwheel's front side is facing your left and you blow into the side of the blades, they will spin quickly counterclockwise if you blow on the top half (into the cups) but will spin slowly clockwise if you blow on the bottom half (against the cups' backs). If your pinwheel were a wind turbine, and spinning counterclockwise turned wind energy into electrical energy, then it would most efficiently produce electricity when wind blows directly into the cups.

More to explore
How Do Wind Turbines Work? from the Office of Energy Efficiency and Renewable Energy
Wonders of Wind (pdf), from the NEED Project Contributors
Fun, Science Activities for You and Your Family, from Science Buddies
Unleash the Power of a Pinwheel, from Science Buddies

This activity brought to you in partnership with Science Buddies