I use this tube to demonstrate Lenz's law. Simply drop a 1" diameter cylindrical or spherical neodymium super magnet down the tube and watch how much time passes before it finally emerges out the bottom. This is the simplest way to demonstrate Lenz's law. These neodymium super magnets are conveniently available on Amazon.com, and they are very reasonably priced. Also a neat yet VERY simple science project.