Key concepts
Physics
Engineering
Mechanical energy
Electrical energy
Wind

Introduction
Wind energy is becoming more and more popular across the U.S.—maybe you’ve even seen a wind farm close to where you live! In 2015 approximately 7 percent of the electricity used in the U.S. was generated by wind. So who knows, when you switch on a lamp in your house that light might be coming from wind energy!

Wind energy is generated by wind turbines. These machines can look like giant pinwheels, and their job is to turn energy from the wind into mechanical or electrical energy. Believe it or not, the wind turbines we use today are based on designs that are more than 4,000 years old!

In this activity we’ll be exploring different turbine designs by testing pinwheels and learning about the factors that can improve their performance.

Background
Wind turbines convert wind into mechanical or electrical energy. One type of wind turbine, the windmill, has been used all over the world for thousands of years to convert wind energy into mechanical energy for tasks such as grinding grain and moving water. More recently wind farms that use turbines to convert wind into electrical energy have become increasingly popular. In some states wind is quickly becoming a major source of electricity. In 2015, for example, more than 30 percent of the electricity used in Iowa came from wind!

In general wind turbines all have the same basic components: blades on a rotor connected to a shaft, both of which are turned by the wind hitting the rotor blades. To make wind energy as efficient as possible, engineers have experimented with many different wind turbine designs. For example turbines can rotate on a horizontal or vertical axis and have large or small blades. And in some cases they can even be bladeless!

Variations in the design of wind turbines are based on where the turbine will be located and how environmental factors will affect its performance. The goal, however, is always to maximize the amount of energy extracted from the wind. You will explore one of these factors—blade shape—to determine how they affect the efficiency of a pinwheel.

Materials

  • Four pieces of eight- by 11-inch construction paper
  • Stickers or tape
  • Three flat-ended pins or thumbtacks
  • Three thin dowel rods or large craft sticks
  • Scissors
  • Ruler
  • Glue
  • Adult helper
  • Pen or pencil
  • Clock or timer
  • Hammer or soft mallet (optional)
  • Fan (optional)
  • Hair dryer (optional)
     

Preparation

  • Cut two eight- by eight-inch squares of paper from two pieces of construction paper. Place one square on top of the other and line up all the edges then glue these two pieces together, making one eight- by eight-inch square. Tip: for a pretty pinwheel, use two different colors of paper.
  • Use a third piece of construction paper to cut out eight, four- by two-inch strips of paper. For each pair of strips, place one strip on top of another and line up all the edges then glue those two strips together. When you are finished you should have four of these four- by two-inch strips.
  • Use your last two pieces of construction paper to cut out eight triangles, each with a base of three inches and height of four inches. For each pair of triangles, place one triangle on top of the other and line up all the edges, then glue those two triangles together. When you are finished you should have four triangles, each four inches tall with a three-inch base.
     

Procedure

  • This activity requires handling sharp materials, please ask an adult to help you with these steps!
  • Start with your eight- by eight-inch square of paper. Fold the square in half diagonally and make a crease. Open it up and fold it diagonally again, this time in the opposite direction. Make a crease, then open the paper back out to the square.
  • Use your scissors to cut from each corner along the diagonal fold, stopping 1.5 inches from the center.
  • You now have a square with four wings or petals. Starting with the topmost petal, gently fold down the right corner of the petal and hold it in the center of the square. Try not to crease the paper. Repeat this with each remaining petal, holding each corner in place in the center with your hand. Tip: Ask an adult to help you hold the petals in place as you work your way around the square.
  • Once all four petals have one corner folded down to the center, hold them in place with a stick or tape.
  • With the help of an adult, push your thumbtack through the sticker or tape at the center of the pinwheel. Use the tack to attach the pinwheel to the top of a dowel rod. (Use a hammer or soft mallet for this step if necessary.) Make sure the pinwheel is held securely but can still turn on the thumbtack.
  • Take your four, four- by two-inch strips of construction paper. Fold each strip vertically down the center then open it back up again so that the paper forms a “V.”
  • Use your ruler to measure one half inch from the short edge of each strip. Use your pen or pencil to make a small mark in the center of the strip, one half inch from the end.
  • With the help of an adult stick the thumbtack through the mark on each strip until all four strips are attached to the tack. Spread them out from one another so they point in four different directions. Use the tack to attach this second pinwheel to the top of a dowel rod. (The hammer or soft mallet for this step may be necessary.) Make sure the pinwheel is held securely but can still turn on the tack.
  • Finally fold each of the four triangles you cut out down the center from apex to base, and then open them back up so each piece of paper forms a “V” shape.
  • Use your ruler to measure one half inch from the apex of the triangle. Mark this point with your pen or pencil.
  • With the help of an adult stick the thumbtack through the mark on each triangle until all four triangles are attached to the tack. Spread them out from one another so they point in four different directions. Use the tack to attach this second pinwheel to the top of a dowel rod. (Use your hammer or soft mallet for this step if necessary.) Make sure the pinwheel is held securely but can still turn on the tack.
  • Test each of your pinwheel designs. If it is windy outside, you can do this by taking them outside and holding them in the breeze. Or you can hold them each in front of a small fan or under a ceiling fan or use a hair dryer on the lowest, cool setting to blow air at your pinwheel.
  • For each test, hold your pinwheel to the wind and count the number of full rotations in one minute. Also observe how well the pinwheel performs in the wind. Which pinwheel seems the sturdiest? Which one seems the weakest?
  • Extra: Test other pinwheel designs. Observe which factors seem to be the most important for creating the best pinwheel.

Observations and results
In this activity you designed and tested three different model pinwheels. Each design you tested had different-shaped rotor blades.

You should have found the first pinwheel, with the folded-over blades, rotated the fastest and most smoothly when placed in front of a fan or in a breeze. The triangle- and rectangle-shaped blades probably did not spin as quickly or as efficiently as the first one you tested.

The difference in performance of each pinwheel was the result of the different-shaped rotor blades that you tested. The first pinwheel’s blade design allowed each blade to capture the most air as it rotated. To understand why this made it move faster, imagine a swimmer racing through the water. With each stroke a good swimmer will keep their hand closed and slightly cupped to try to capture the most water. This allows the swimmer to “push” against more water and propel themselves forward. You can imagine if they spread their fingers wide and allowed the water to flow through, they wouldn’t be able to push themselves through the water as quickly.

Your first pinwheel design is based on the same principles. Because it’s folded over it acts like a pocket for collecting air. The more air it can collect, the more efficiently it will be pushed around the rod. The other two pinwheel designs did not collect air in the same way. The wind moved past but did not bump into the blades on those versions; therefore they weren’t pushed as quickly or smoothly as those on the first design.

Now that you know the basics of pinwheel rotor blade design, try to make the most efficient pinwheel you can!

More to explore
Unleash the Power of a Pinwheel!, from Science Buddies
Spinning Your Wheels: Pinwheel Sensitivity, from Science Buddies
Spinning Symmetry with Pinwheels, from Scientific American
Science Activities for All Ages! from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies