This Christmas we all drove down to Georgia to hang out with my parents, my sister and her kids. I am busy writing engineering challenges these days so decided to use these eager guinea pigs to test out some ideas. The first one was such a big hit we didn’t get to any others.
We made boomerangs and they actually came back!
The kids spent at least 2 hours throwing these around outside. And only one got stuck on the roof.
The best part is, they were super simple to make. Even the 4 year old got in on the action. Here’s what you need:
That’s it. Nothing special. Unless you ant to add in crayons and markers for decorating.
Our boomerangs started out as 2 strips of cardboard, 2 inches x 14 inches long. Then tape or staple them together in the middle at right angles to make a cross. Again, that’s it!
You can experiment with width and length of the pieces, rounding the edges or even bending the top inch or two upward. But the basic design worked just fine for me.
To throw, hold the boomerang vertically and give it a quick snap with your wrist. You want a good fast spin. It will go up, curve around and come right back to you.
So how does it work?
When you throw a boomerang you give it a forward push or force as well as spin or torque. The top blade of the boomerang is spinning forward and moving forward so it is going very fast. The bottom blade is moving forward but spinning back and moving much slower. This difference in speed gives the top blade lift from the air. The unbalanced lift on the top of the spinning boomerang pushes it into a circle so that it travels back to you.
If you want a more in depth discussion on the upper high school, college introductory physics level (and instructions for a simple 3 arm boomerang) check out this video by the Science Samauri. or this page from HyperPhysics (click on the graphics for an explanation)
Why a 4 armed boomerang?
First of all these 4 armed boomerangs are much easier to make and throw than the kind you see in Australia. And second of all, the ones you see in Australia were never used by the aboriginal people for hunting. They just used plain old sticks that they could throw very accurately at animals while hunting. One day some guy made a curved stick shaped like an airfoil (rounded top, flat bottom) and when he threw it, it curved around and came back. Not very accurate or useful for hunting, but great fun to play with while you’re waiting around for the kangaroo meat to cook. You can find other instructions for more complicated 4 arm boomerangs like this one from NASA