Light balls, disks, and cylinders will levitate on a stream of water in a surprisingly off-center way. In this episode of Veritasium, Derek Muller teams up with Blake from InnoVinci, with some help from aerospace engineer Nicole Sharp, to film and figure out the physics behind this trick:
The standard Bernoulli effect relies on the object being completely immersed in the upward-flowing fluid. But in this case the water seems to form a single stream around the object and it’s deflected away and down from the stream. By Newton’s third law, the force on the water by the ball is equal and opposite to the force of the water back on the ball, pushing it up into the stream. There is a stable equilibrium position because if the ball moves into the stream, it “cuts off” the water going over the ball so it drifts out. If it drifts out too far, then lots of water passes over the ball, pushing it back into the stream.
Want to try this experiment yourself? Check out DIY Backyard Levitation:Next: Surprising Applications of the Magnus Effect, The Physics Behind a Curveball, Electromagnetic Levitation Quadcopter, and more levitation.
Plus, more backyard physics experiments: How to make Leonardo da Vinci’s self-supporting bridge and The Stacked Ball Drop (and Supernovas).