Wind forces on a skyscraper can set it swaying, so engineers design dampers to stop the motion and keep users comfortable. Some buildings use suspended solid mass dampers to counter a building's motion, but others take a liquid approach.  (Video and image credit: Practical Engineering) Read the full article

The sloshing of liquids inside solids is usually presented as a difficulty to overcome, as with the transport of tanks, the motion of fuel in satellites, or even the problem of walking with a full cup of coffee. But liquids also make a very effective damper, as in the case of a bouncing ball partially filled with liquid. Here we see high-speed video of the liquid's motion inside the ball as it bounces and rebounds. Part of the ball's kinetic energy at rebound is transferred into the fluid jet, reducing that available for the ball to transfer into potential energy. (Video credit: BYU Splash Lab)

In this high-speed video, two flexible spheres are dropped from the same height. The one on the left is filled with air, the other is partially filled with a liquid. Although both spheres rebound to nearly the same height after the first bounce, their behavior differs drastically after that. The sloshing of the liquid inside the sphere acts as a damper, absorbing energy that would otherwise cause the ball to continue bouncing. The effects of contained liquids sloshing are important for understanding the dynamics of tankers, fuel on spacecrafts, and even how to walk without spilling your coffee.