About a month ago, I had an extraordinary experience:
It was Bill Nye standing on me while I laid on a nail bed. Lots of fun, for sure, and I pointed out to the audience that it was the one shot I wanted from the whole gig. The way we set that up was to first have him stand on my chest without the nail bed, but we cautioned that it would be much safer to use the plywood on top. We talked about how we’d be able to spread Bill’s weight over several contact points on me: my thighs, my chest, and my hands. That’s when we decided to take it up a notch with the nail bed.
Now I’ve been using the nail bed for over 10 years and it’s usually a big hit. Sometimes I do a decent job of talking about the physics, but I’ll be honest that sometimes the show’s running long on time and we just do it (and the breaking of the cinder block) for show. What I wanted to talk about in this post was an idea I had about talking even more about the physics of distributing force. What’s funny is that I’ve talked to a few different people about this (including my partner and my sons) and, while they agree that it adds to the physics, they don’t think it’s appropriate for the show. So I’m looking for your second opinion. Thanks in advance🙂
The reason the nail bed works (and why I can handle Bill (we’re on a first name basis now, you see) standing on my chest) is NOT that I’m reducing the total force on my body, but rather than I’m distributing that force over a larger area. No single nail has enough force to puncture my skin, for example. This got me thinking about pillows.
When I was in school, I was always a little confused about pillows. My free body diagrams kept telling me that it didn’t matter what I rested my head on, something had to provide a force equal and opposite to my head’s weight to keep me from smashing my head on my bedroom floor. This made sense to me from a free body diagram perspective, and certainly I could do all the homework, but it always bothered me how that perspective didn’t seem to explain the softness of pillows. What I mean is that feather pillows seem much more comfortable than, say, cement pillows but they both must be providing the same force.
I know now that really pillows deform to your head, providing a very large surface area to spread the force out. What I figured on doing for my show was to concentrate on adding more and more pillowy-type substances between me and the plywood while people are standing up there. We’d slowly go from all the weight on my thighs/chest/hands all the way up to the weight on every part of my upward-facing body, using foam or something.
The reason my family and friends think this isn’t a good idea is that people would say “oh, he just has a pillow up there, of course he’s ok” instead of “ahh, I see, the pillow disperses the weight so that no single part of his body has to support a lot.”
So what do you think?
Some comment starters for you:
- I’m a student in this class and, wait, nevermind
- I saw that show and Bill was great.
- I’m not sure I follow what you mean by the free body diagram. Would you, by chance, happen to have a new Surface Pro that would allow you to draw a nifty picture?
- Wait, I thought feather pillows were better than cement pillows because . . .
- Wait, they make cement pillows?
- Sure, do this in your show, I’d love it if you got crushed.
- Don’t put this in your show, but for this reason instead . . .