Other Technology

Linear Momentum Machine

Everyone knows that a bundle of angular momentum (a gyroscope) has some strange properties. But few people realize that a bundle of linear momentum is equally bizarre!

This is a linear momentum machine to let you safely explore the weirdness of momentum, standing waves, solitons and wave propagation.

Chain will avoid anything it touches The chain piles into your palm like a waterfall, but doesn't tangle The chain makes an intricate 3d dynamic sculpture An endless supply of ever-changing patterns Solitons travel down the left chain

Questions You Can Study

If the bottom of the chain hits a bump, then it avoids the object it hit. How does it "remember" where the object is?

As you can see (if you build it!), the waves travel slowly upstream along the direction of movement. If you increase the chain speed, will the waves no longer move upstream?

This device is interesting to catsWhy do cats think it's alive?

Why does a soliton keep a constant height but get a shorter wavelength as it reaches the bottom?

How slowly can the chain move, while the system still exhibits some weird properties?

How does the behavior change when it goes really fast?

If you replace the chain with something heavier, what behavioral changes will occur?

What happens if you pinch the down-chain and hold a link in place?

And many more quirks to discover...


There are many ways to make a lightweight chain travel at modest speeds. I describe how to build one model with a 12v dc motor on a cheap K'nex framework, but almost anything will work!

Where Did This Come From?

Lariat Chain by Norman Tuck Not from outer space, although it is strange enough to be alien!

I saw this machine at the San Diego science museum (Reuben H. Fleet Science Center) in December 2000. Their model was turned by a bicycle wheel with the rubber tire removed, and mounted high enough to avoid most people's fingers. The steel rim made an excellent pulley. The large diameter allows waves to travel through the bottom without tangling. A small electric motor turned the wheel at modest speed.

The display is called a Lariat Chain and is a twelve-foot tall kinetic sculpture by Norman Tuck. There are models on display at a dozen or more museums around the world (see his web site for details). Some more extremely interesting devices are also described at his web site of www.normantuck.com.

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