I’ve always wanted to build a bed of nails, especially since I started teaching physics. Now I’ve done it.
I built it at Home Depot in Salem, MA. The main advantage was that this meant easy access to a table saw and a nail gun (and someone to teach me how to use one).
The Nail Gun
Using the Nail Gun
After 3,300 nails, the bed is complete:
The Finished Product
And it works!
Trying it Out
If you’re curious for specs, the bed is 2′ × 6′, and I spaced the nails ¾” apart.
Now I need to sneak it into the school so my students won’t see it until we study pressure, which should be in a couple of weeks.
Give away all the circus sideshow secrets, will you? Next you’ll let them know that walking on glass works almost the same way! We’ll send clowns to throw buckets of confetti at you.
Actually, the people who understand the physics behind the tricks tend to be more likely to buy tickets so they can show these things to their children. So in a sense, I’m actually throwing buckets of money at the clowns. 😉
One of my someday goals is to learn how to safely set up a firewalk. The Firewalking Institute of Research and Education (F.I.R.E.) offers firewalk instructor training courses for about $3500. This is undoubtedly necessary if I’m ever going to have an asbestos flip-flop’s chance in hell of setting up a firewalk at school.
None of your students read your blog? And Home Depot will let you use their nail gun in their store? Holy liability, Batman! 🙂
But other than that, awesome! So what is the total surface area of the tips of the bed of nails? And how do you get onto it? Your butt is much smaller than your whole body.
Yes to both. But only a few of my students check my blog often enough to actually notice, and they’ll probably be good about not giving away the secret. (Part of the fun for the few who are in the know is watching their friends be surprised.)
A little unscientific Google searching suggests that the tip of a nail is around 0.1 mm2. The spacing of the nails is ¾”, so this means the nails would account for approximately 0.06% of the area of the board. Or put another way, the pressure of a flat object sitting on the nails is about 1750 times what the pressure would be if the flat object were sitting on the board instead.
As for how to get onto and off of a bed of nails, eHow.com has instructions for How to Lie on a Bed of Nails. I followed their advice and it worked. The one thing they left out that I found from another site is to keep your head off the nails or have a separate pillow/headrest. Because the back of your skull is curved, it’s not possible to distribute the weight of your head evenly over a large number of nails.