Snow geometry

"Linkage" is a technical/mechanical name for a relatively simple concept that's played a big role in daily life since the Industrial Revolution.

Imagine four rigid bars of different lengths, connected into a chain by three mobile joints. Add one more joint to the end, close the loop, and you have a linkage. You can use that linkage to change one type of motion—say, a spinning motor—into a completely different, usually very specific, type of motion. For instance, the windshield wipers on your car swish back and forth in time, the way they do, because their movement is controlled by a four-bar linkage similar to the one I just described.

Recreational mathematician Vi Hart has another way of explaining linkages, involving a good, fresh snowfall and the human body. Enjoy!

Thanks for Submitterating, akputney!