Your mission
A paper helicopter has no motor and no batteries. You just let go, and it spins all the way to the floor. How?
Work through each tab in the menu. Read how it works, then show your thinking. Each tab you finish earns a badge.
Earn all six badges to unlock the secret build plans. Then you get to make a real one and test it.
My badges
Teacher note
- For each student: 1 strip of copy paper (2.5 by 8.5 inches, so one sheet makes 4 strips), 1 to 3 small paper clips, scissors, a ruler, and a pencil.
- For the class: a stopwatch or timer, a tape measure, and one safe high spot for drops.
- Everything is normal classroom supplies, so there is nothing to order.
- The build plans unlock after all six badges are earned. Progress is saved on this Chromebook only.
- The Flight lab is a simple model. Real drop times will be different, but the patterns match: bigger blades fall slower, more weight falls faster, and shorter blades spin faster.
- Extension: have students test copy paper against cardstock, changing only that one thing.
Gravity against air
Two forces play tug of war with your helicopter the whole way down.
Read: the tug of war
A force is a push or a pull. Two forces act on a falling paper helicopter.
Gravity pulls the helicopter down toward the ground. Gravity pulls on everything, all the time.
Air resistance pushes up against the helicopter. Another name for it is drag. Air is made of tiny bits you cannot see. A falling object has to shove those bits out of the way, and they push back.
The flat paper blades are wide, so they catch a lot of air. The more air a shape catches, the bigger the drag. That is why an open umbrella is hard to pull through the wind and a closed one is easy.
Picture it
The helicopter's speed limit
It speeds up at first. Then something surprising happens.
Read: terminal velocity
When you first let go, the helicopter is slow. Gravity is winning, so it speeds up.
Here is the trick. The faster something falls, the harder the air pushes back. So as the helicopter speeds up, the drag grows too.
Very soon the air push is exactly as big as the pull of gravity. The two forces are balanced. The helicopter stops speeding up and falls at one steady speed.
Scientists call that steady speed terminal velocity. You can think of it as the helicopter's own speed limit.
Try it: slide the speed
Why does it spin?
Nobody twists it. The air does all the work.
Read: two pushes make a turn
Look at the two blades. One is bent toward you. The other is bent away from you. They tilt in opposite directions.
As the helicopter falls, air pushes up on each tilted blade and slides off to the side. When a blade pushes air one way, the air pushes the blade back the other way. Every push has an equal push back.
So one blade gets pushed one direction, and the other blade gets pushed the opposite direction. Two pushes on opposite sides, going opposite ways, make a turn. It works like two kids pushing on opposite sides of a merry go round.
Scientists call this turning push from the air rotational lift.
Try it: view from above
Blade A is bent toward you.
The job of the paper clip
It looks like the least important part. It might be the most important.
Read: center of mass
Every object has a balance point. It is the spot where all its weight seems to gather. Scientists call it the center of mass.
Paper is very light. A paper clip is heavy for its size. When you clip it to the bottom, the balance point moves way down low.
When something falls through air, its heavy end leads the way. A low center of mass keeps the clip pointing down and the blades pointing up, right where they can catch the air.
Take the clip off, and nothing tells the helicopter which way is down. It flutters, flips, and tumbles like a leaf.
Try it: move the weight
Heavy end down. Steady.
Where the energy goes
You give the helicopter energy before it ever moves.
Read: stored energy and motion energy
Lifting the helicopter high takes work. That work gets stored in the helicopter as potential energy. Potential energy is stored energy. The higher you hold it, the more it has.
When you let go, the stored energy starts changing into kinetic energy. Kinetic energy is the energy of motion.
The helicopter moves in two ways at once. It moves down, and it spins. Both of those motions are kinetic energy. A little energy also goes into stirring up the air.
Energy is never used up and it never appears from nowhere. It only changes from one form to another.
Big idea: Change. The helicopter's energy does not disappear on the way down. It changes form.
Try it: lower the helicopter
Flight lab
Design a helicopter, drop it from 3 meters, and watch the numbers. Finish all four missions to earn the Test Pilot badge.
Design it
RPM means rotations per minute. It tells how many times the blades would go around in one minute.
Height over time
The dashed line is your last drop, so you can compare. The dot shows when the helicopter reached its top speed.
Missions
This lab is a model. A real paper helicopter will not match these numbers exactly, but the patterns are the same.
Build it
The build plans are locked
Earn all six badges to open them. You still need:
You earned it. Time to make a real one.
How to build your helicopter
You need: a strip of paper, scissors, a ruler, a pencil, and one paper clip.
- Cut a strip of paper that is 2 and a half inches wide and 8 and a half inches long.
- Make the blades. Cut straight down the middle from the top. Stop after 3 and a half inches.
- Measure 4 inches down from the top. Make one small cut on each side there. Each cut goes in three quarters of an inch.
- Fold the two sides below those cuts in toward the middle. Now you have a skinny body.
- Fold the bottom half inch up. Slide a paper clip over the fold.
- Fold blade A toward you. Fold blade B away from you.
- Hold it up high by the body with the paper clip pointing down. Let go. Do not throw it.
Stay safe: keep your feet on the floor. For a higher drop, ask your teacher to do it.
The plan
Solid lines: cut. Dashed lines: fold.
Test like a scientist
Change only one thing at a time. That is how you know what made the difference. Drop each design three times from the same height and time each drop.
| What I changed | Drop 1 (s) | Drop 2 (s) | Drop 3 (s) | Average |
|---|
Ideas to test: add a second paper clip, trim the blades shorter, fold the blades the other way, or build one from thicker paper.