When we build super-tall skyscrapers, those buildings are subject to swaying due to wind and seismic activity. They're designed for it, and some amount of movement is both safe and inevitable...but it can be really unpleasant for people in the upper floors. So what can engineers do to reduce this movement, but preserve the flexibility of the building?

Enter tuned mass dampers (previous coverage). TMDs are used in all kinds of things, from cars to power lines to spacecraft (!). They offer a counterweight that offsets vibration, counteracting the most troubling movement within a given structure.

Okay, so how do TMDs work? In this video from Practical Engineering, we get a great demo, including a small-scale build in the video-maker's garage to show the effects of a simple TMD system. Tune in and learn a bit of awesome engineering:

(Note: Bonus points for the googly eyes on the demo skyscrapers! If only we had those on real skyscrapers....)