For building a bridge at the Bridge Building workshop sponsored by the National Engineering Month at the Science Centre, I got a yoyo so I got to thinking "who invented a yoyo?" and "how does it work?"History:
as old as 1000BC (3000 years old)
oldest surviving 500BC (2500 years old)
1st patent in 1886 in US
elements: 2 discs joined by 1 axle, which has a string attached (by knot or slip)
materials: plastic, metal, wood, turtle skin
disc shapes: imperial, concave, convex
axle: butterfly (wider gap)
Word origin: Tagolog (Philipines) word meaning "come come"
Two ways to attach the string to the axle:
1. knot (can't "sleep")
2. looped slip string: by using a constant string, 2x the desired string length, twisted, and slip the axle through at the midpoint; Philipine design
My yoyo:
diameter=6 cm
radius: 3 cm
circumference: 19 cm
area: 28 square cm
If this yoyo were an oval, it would spin around and not work properly (like a helicopter top blade with 3 blades placed like 4).
Experiments:
http://www.yo-yo.com/lessonplans/yo_yo.pdf
