See, if you make an electromagnet and attract something like a steel bolt, that bolt actually becomes a small magnet itself. If you then reverse polarity on your electromagnet, the bolt's magnetic field will also reverse. If you do the reversing fast enough, however, there isn't time for the bolt's magnetic field to reverse, and the two magnets repel each other. If you have a very powerful and somewhat dangerous electromagnet, the bolt becomes flying shrapnel.
You can make an electromagnet powerful enough to hold up 250lbs using some wire and four AA batteries. But that's not powerful enough to propel a Pinewood Derby Car to first place! No, you need something with a bit more power. Like a 12volt, 125amp Cold cranking car battery.
Car batteries are different from AA batteries in that they can kill you in many ways. It takes a single amp across your heart to stop it, cold. Most car batteries have at least 100 amps, and many deaths occur from people accidentally completing a circuit with their body. Also, if you accidentally short out the two terminals of a car battery by dropping a wrench across them, for example, not only will the wrench weld itself to the battery, but the battery will heat up rapidly. If the wrench is not removed quickly both the wrench and battery could explode, showering the vicinity with caustic sulfuric acid and molten metal.
This is dangerous, kiddies. DO NOT try this at home. I didn't. I tried it at work. My workplace is good for such experiments because it has other trained technicians, expensive and useful computers and test equipment, and a great sprinkler system. So I haul my supplies there.
My highly skilled coworker, Frank, eagerly helps me hook up the circuit. I've got jumper cables, standard 3-way light switches, a small bit of house wire, and a giant battery. What could go wrong? I put on gloves and safety goggles and think twice.
"Hey, Frank, do you think the light switch might melt?" Frank assured me it wouldn't: "Nah."
Sparks flew as I warily hooked up the last jumper cable clamp, ready for anything.
Nothing happened.
Then the house wire crackled loudly and expelled a huge puff of smoke. I leaped backwards in self defense. Frank started yelling "Shut it off! Shut it OFF!" like a manic two-year-old. And then I realized something. The battery was shorting out. I quickly gathered my courage and extended my 3 foot long arm about 3 and a half feet and turned off the light switch. Frank frantically hacked through the housewire with a packing tape dispenser.
Only then did we comprehend the smoke was rising towards sprinkler system. That would not be good for all the expensive electronic equipment in the room. We were two Keystone Kops looking for a vacuum. I stood on the workbench, my head an inch from the ceiling and blew at the smoke cloud. Frank finally found the vacuum (and power cord) and I started roaming the room, sucking in smoke as fast as possible.
You'll be glad to know the sprinklers never went off. We were glad, anyway. We did a quick look around like naughty 10-year-olds and found, to our relief, no one in building had seen our exploits. Then we did what any clear-headed men would do in such a situation. We hid the evidence and ran away. Well, walked away, on a "break."
Later that day I cut open the light switch with a dremel, which stunk a little as it melted the plastic cover. It didn't stink nearly as bad as the leftovers from "the experiment", though. When I finally opened the switch, I saw that it had indeed melted, acting exactly like a fuse. I hadn't actually done anything when I had so bravely shut it off.
My boss came in the room right then and asked what that terrible burnt smell was. I pointed to the dremel and the light switch and he nodded knowingly, "Oh, I thought it was a short circuit."
Frank and I looked at each other for a moment, and laughed our heads off. I'm buying bigger switches next week. Frank swears he won't help me anymore. That's fine. All the Pine Wood Derby glory shall be mine.
