How a key works.
I could watch this a million times
Pneumatic Sponge Ball Accelerator
Here’s a video of the “Pneumatic Sponge Ball Accelerator”, installed at the Tschumi Pavilion in Groningen / The Netherlands. The apparatus contains 1000 black sponge balls, which are sucked through 150m of transparent pneumatic tubes with the power of a regular household vacuum cleaner. The balls travel with a speed of about 4m/s. Visitors can operate the machine with a touch sensor mounted on the pavilion’s front glass: They can change the direction of the airflow and watch the balls speed up, slow down and reverse.
You can find out more at Roy’s website here