What it Shows

Inspired by Richard Feynman's story in his 1985 book (pp 63-65), Surely You're Joking Mr. Feynman, the demonstration answers the question "which direction does a lawn sprinkler spin if water enters the nozzle rather than being expelled from the nozzle?" The reverse sprinkler spins in the opposite direction of a "normal" sprinkler. "Dissipative effects" has been the hand-waving reason for the past 30 years, but the real reason why it spins in the reverse direction is far from obvious (see Comments, below). It turns out that a sprinkler designed to be "truly...

Vector representation of position, velocity, and acceleration.

What it shows:

A circular train track¹ is mounted on a board. X-Y axes are painted on the board with the origin at the center of the circle. Vector Arrows (Newtonian Mechanics, Vectors and Forces in Equilibrium) representing position, velocity, or acceleration may be attached to the train to...

What it shows:

A simple and convincing demonstration of the intermediate axis theorem. Consider an object (a tennis racquet in this case) with three unequal principle moments of inertia. If the racquet is set into rotation about either the axis of greatest moment or least moment and is thereafter subject to no external torques, the resulting motion is stable. However, rotation about the axis of intermediate principle moment of inertia is unstable — the smallest perturbation grows and the rotation axis does not remain close to the initial axis of rotation.

How it works:...

What it shows:

In explaining the electron orbits in the Bohr atom, de Broglie's principle of particle wave duality allows you to treat the electrons as waves of wavelength nλ = 2πr where r is the radius of the orbit. Then the only...