A Box with a Secret – See, Mom, Physics can be Fun!

Puzzle Box-1Beck wanted to build a locking box to keep safe the valuable things 9 year old boys collect (most of them are dead). A quick accounting revealed we had the required stuff:

Old cedar from a recently demolished closet… Check.

Tools… Check.

Can-do spirit… Check.

Twenty fingers… Check (I like to count them before and after. I find if you wait too long, it is harder to clean out the sticky pieces lodged in the machinery).

Instead of a typical box with a padlock, we went minimal. Aesthetically it’s just a box, nothing special, but what makes it cool is its locking mechanism. Everything is flush except for a single, solitary knob on top. The knob doesn’t appear to do anything. It doesn’t turn (much), or lift up, and cannot be pushed in any direction. While you can hear things sliding around inside the box, no matter what you do, opening it appears impossible. Unless you know the secret.

The secret is centrifugal force. You probably guessed that.

Puzzle Box-7

The box’s top is secured in place by six sliding pins (nails, actually). The box remains locked no matter how it is tilted because when some of the pins slide to the open position, others slide closed. In order to open the box, you must place it on a flat surface, knob on top, and spin it. Centrifugal force slides all of the pins to the outer edges of the box allowing the top to be lifted off.

Puzzle Box-3

Yet, even the wonders of physics won’t open the box unless you first orient the seemingly useless knob so a pin can slide through a slot under the knob, all the way out, when the box is spun. Nobody has ever figured out the secret on their own.

Here’s what the inside looks like (dead things not shown for clarity). It’s not elegant, but hey, it was our first try!

Puzzle Box-8

We didn’t build from plans because Beck likes to “Free-build,” or as I call it, “Wing-it and rebuild it ’til mom makes you practice piano.” Thankfully the box was simple and the mechanism easy to “wing.” Someday, though, I’ll chain Beck to his desk for 5 minutes of pre-planning work, just to teach him the “right way” to design. I’m not sure if the chains they use to anchor battleships are strong enough. Might need to add some super-glue and barbed wire, too.

Puzzle Box-9

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Tim Bjella

Principal architect and interior designer for Arteriors / Bjella Architecture.

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