Some of the best and most enjoyable demonstrations of physics principles can be put together quite readily with very cheap materials. A good example of this was the simple version of the Magdeburg hemisphere demo I discussed previously; another example is the approximately $20 device shown below.
A pair of rails spread apart as they increase in altitude: they are 3” high on the right side, and 4” high on the left. This is easier to see from a side view.
A pair of plastic funnels have been glued together at their wide ends; when the joined cones are placed on the right, lower, side of the device, they immediately roll to the left, stopping only when they hit the uprights on the far left side. The joined cones have rolled uphill, in seeming defiance of gravity!
Of course, this simple device can be readily explained by physics, and its unusual operation can be used to highlight an important principle in the physics of forces and motion.
Skulls in the Stars 