Things that rotate turn around a center point.
Rotate means to turn around a fixed center point or axis; Two dimensional objects, such as the CD shown, rotate around a stationary center point; Three dimensional objects turn around a stationary axis, which is an imaginary line running through the object;
The top shown is an example of a 3-D object rotating about its axis, which is an imaginary stationary line running through the top.
The Sun and planets in our solar system all rotate about their axis.
Discover Rotation for Yourself
Make paper helicopters.
1. Fold a piece of copy paper in half from side-to-side. Fold the paper in half again in the same direction.
2. Unfold the paper and cut along the fold lines to form four strips about 2 inches (5 cm) wide.
3. The pattern shows where one of the paper strips is to be cut and where it is to be folded. Note: The two horizontal cut lines are midway between the top and bottom of the strip.
4. The last steps for preparing the helicopter is to bend the folded end of the tail up.
Then bend the right wing forward toward you and the left wing backwards.
Before testing the helicopter, ask kids to predict which direction the paper will rotate. This is also called a hypothesis.
The direction of rotation must have a reference of observation. Observe the rotation from above the falling craft.
5. Now it is the time to test the predictions (hypotheses). Give the following instructions:
- Hold the body of the helicopter with your thumb and index finger placed under the wings.
- Hold your arm as high as possible and drop the craft. Try not to let the craft hit against your body or clothes.
- Important: Keep your feet on the floor. Note: I give this last step when working with a large group of kids. I do not want them jumping and throwing the craft nor standing on chairs or tables, etc……………
If the paper doesn’t rotate well, often it is because the wings have been bent too much. Correct this problem by laying the paper flat and gently rub your fingers over the wings.
Results: Observing the falling helicopter from above, the wings rotate in a counterclockwise direction around the crafts axis which exits between the two wings and the end of the tail.
Before giving any explanations for why the paper craft rotates, introduce the following challenge
How can the paper helicopter be modified so that it rotates in the opposite direction.
I have had some really interesting idea, especially from young kids.
- Hold the paper helicopter in your other hand.
- Turn and face the opposite direction before dropping it.
- Give the paper a twist in the clockwise direction just before you drop it. One girl insisted that this works and it did. The variable that I had not considered was the height the paper was dropped. The girl was short and the falling time was not long enough for the helicopter to “recover” and fall counterclockwise.
Give kids an opportunity to test different hypothesis. They will discover that when the wings are bent in the opposite direction, the helicopter will spin clockwise.
Why the Paper Helicopter Rotates
As the paper helicopter falls, its wings hit against the air. The air is free to rush out from under the wings in
all directions except where the wings attach to the body of the craft. When the right wing is folded toward you and the left wing folded backwards, the force of the air against the body of the helicopter causes it to rotate.
Think about it!
Air is pushing on the body in two different directions. The result is that the paper rotates in the direction of the the two turning forces acting on it. Flip the wings in the opposite direction and Voila’ the helicopter rotates in the opposite direction of clockwise.
Books with More Rotating Activities
1. 204 Sticky, Gloppy, Wacky, & Wonderful ExperimentsExperiment #15 Demonstrates why the rotation direction of Venus is reversed from that of Earth.
2. Super Science Models : Stars and constellations that are above the horizon in the Northern Hemisphere appear to rotate as a unit around Polaris.