When two different size soap bubbles are connected together, the smaller diameter bubble will shrink and collapse to blow up the larger diameter bubble. One can use this to demonstrate Laplace's law or the phenomenon of minimizing the surface area of a soap film.
How it works:
Laplace's law tells us that the gauge pressure of a spherical membrane is given by 2γ/r, where γ is the surface tension and r is the radius of the sphere.1 For soap bubbles (which have an inside as well as outside surface), the gauge pressure is twice this: 4γ/r.… Read more about Double Bubble
A physical pendulum finds stability in its inverted position when driven at the proper frequency and amplitude combination.
How it works
The physical pendulum is a 45 cm x 2 cm x 6 mm (1/4") strip mounted on a ball-bearing pivot and can rotate 360 degrees. Its pivot is driven by a 3/4" stroke Sears Craftsman Auto Scroller Saw (model 315.172090) at about 50 Hz. The basic idea was adapted from Michaelis4… Read more about Inverted Pendulum
Bringing a charged rod close to neutral dielectric polarizes the dielectric's surface charges. Here a pile of Styrofoam puffs are polarized and attracted to a charged rod.
How it works:
The neutral puff experiences a non-uniform electric field from the rod. Although there are polarized charges of both kinds, because (figure 1) the field is stronger near the rod due to the concentration of positive charges, there is a net attraction. On a dry day they'll jump to meet the rod.