Head to your garage or tool shed and see how many tools you can hang from one magnet. A sledge hammer followed by a monkey wrench would be impressive, as would an entire wrench set in one chain (sorted from largest to smallest, of course.) Or why not forgo a tool belt for your next construction project, and stick a couple magnets in your pockets instead? Your tools will seem to adhere to you for no reason.
Note that even brief exposure to neodymium magnets is enough to make your tools temporarily magnetized. Your hammer will most likely start sticking to nails for a time after doing this.
Have an old CRT (non-flatscreen) computer monitor or television you’re soon to recycle? Have some fun with it first. Turn it on, put a neodymium magnet in your hand and move your hand directly in front of the screen. This will prompt a psychedelic color show like you’ve never seen before. Note that doing this to a monitor or TV you’d like to keep using is a bad idea, as it can cause permanent damage. This is why you don’t store neodymium magnets in your computer desk.
Copper Pipe Levitation
This one works best if you have a marble handy for contrast. Take a copper pipe, hold it upright, and drop the marble through the pipe. Take note of how long it takes for the marble to fall through—it should happen almost instantly. Now drop a neodymium magnet the same size through the pipe. That will take much longer to work its way through—usually a couple of minutes depending on the strength of the magnets.
This happens because copper, while not attracted to magnets, it is a very good conductor. Conductors like copper create an eddy current when exposed to magnets, which in turn causes the braking that slowed the magnet’s journey down through the pipe.
If you have a cassette tape around that you don’t mind parting with, a neodymium magnet is as good a method as any to render it useless. Putting the magnet near the tape is enough, or you could leave it there overnight. Point is, your relic from the 80s will cease to function. This is because data on a cassette tape is arranged magnetically, and as such magnets can rearrange it, distorting it or making it useless altogether. Really powerful magnets can rearrange it really quickly.
If you don’t know what you’re doing, it’s probably not a good idea to play with neodymium magnets much bigger than what you’d find in your standard toy set of magnets. The bigger the magnet, the more powerful the force, the greater the overall risk. Anything larger than an inch squared is powerful enough to pull together with the force of hammer-on-nail, so keep it smaller than that if you can.