Introduction: How to Make a Gravity Puzzle (Brain Game)

About: Random Weekend Projects

Step 1: Watch the Video!

This little brain game is all about engineering a lower center of gravity. The idea has been around forever, but most people still can't do it. The challenge is simple .. just balance these 14 nails on one nail head.  The nails can't touch anything except each other, and they all have to be balancing at the same time.

In this project you'll learn how to make a fun little mind puzzle, for giving as a gift, or for entertaining guests.  You'll also learn the secret to getting all nails these to balance at once!

Watch the video to see how to make a simple, but nice, presentation platform for the puzzle!

Step 2: A Look at the Finished Project

All this project really needs, are about 15 framing nails (3" work well), and something to hammer one of them into.  It's as easy as that!

However, to make this into a proper project, you're going to need to glorify the idea a little by making a nice presentation stand.

I used a simple spreadsheet program to make a template that would accommodate the 15 nails on a board of wood, with one nail right in the center.

If you like it, you can have it for free.  Download it here.

Step 3: Make the Nail Base

I found a piece of scrap wood at a local hardware store (Home Depot) that they just gave me for free, but they will usually sell scrap pieces for about $0.50 each.

By taping the template to the top of the wood, it's quick and easy to make the cuts and drill the holes.

There are 15 holes in the template to accommodate 15 framing nails.  It's important that the nails have flat heads at the top, and you'll see why later on.

We want holes that allow us to manipulate the nails in and out, but small enough to prevent them from flopping around.  I found that a 9/64" drill bit worked perfectly with these nails.

When drilling the holes, make sure you don't drill all the way through the wood, unless you plan to glue another piece to the base.  I used a drill press to gauge the depth of the holes, and after drilling all the holes, I inserted nails to make sure all the tops were level.  

Now the edges can be cut.  I used a chop saw to make the cuts, and at this point you are finished with the template.  The paper can be removed and thrown away.

To make the nail base look more professional, I used my router table and a beading bit to sculpt the edges, then some fine sandpaper to clean it up and get it ready for staining.

I used a rosewood stain because it's what I had on hand.  2 coats of stain went on, letting it sit for 3 minutes before wiping off the excess, and then finishing it with some shellac to add some gloss and seal the wood.

At this point, you should have a nail base that looks like the one in the pictures.  

It might seem like a lot of work, but it's really pretty simple, and remember, you can use this as a decoration piece, or a game for entertaining guests .. so take some pride in your work! 

After it's dried for a couple of hours, it's finished and ready to use on your friends!

Step 4: Alternative Nail Bases (If You're Feeling Lazy)

Of course if you're feeling lazy, or don't have the tools to put this much work into the project, you can just use a hammer and a scrap piece of wood.

If you don't have a hammer, maybe you can find a rock?

If you don't have wood, hammer, or a rock, hopefully you have someone who likes you enough to just hold the nail upright?

It's really that easy.

Now for the challenge!

Balance the remaining 14 nails on this one nail head.  The nails can't touch anything except each other, and they all have to be balancing at the same time.

While this trick has probably been around since before any of us were born, most people still don't know how to do it!

Step 5: Solving the Puzzle

Have you tried to solve the puzzle on your own yet?

You may want to give it a go before seeing the solution.  This is one of those puzzles that seems impossible, until you learn the super simple pattern that makes it work .. then it's easy!

Solving the puzzle:

Start by placing a nail on the table, then staggering the other nails on top, so they alternate directions, as seen in the pictures, and so that there is just enough room between the opposing heads so that the last nail can be laid down on top.  This last nail faces the opposite direction to the first one laid on the table.

Now you can take the nail on the bottom, and slowly lift upwards until the other nails drape down, binding their heads on the top overlaying nail.  

From here it's easy to balance the entire contraption on the lone nail head.  

The center of gravity is now lower than the balancing point, so this structure is fairly stable, and resists falling when it's bumped, blown or tapped.

For another challenge, see if you can balance 15 wooden matches like this. It's much harder, but once they balance they are amazingly stable as well!

Step 6: One More Challenge

I found that when the contraption is balancing, the nails could be pushed closer together, and more nails added.  I got each unit up to 23 nails!

The next question was how many could be stacked on top of that?

I repeated variations of this pattern and stacked 4 units of about 22 nails each, for a total of 89 nails balancing at once!

How many can you get?

If you haven't seen the video yet, you can still see it here!

If you like this project perhaps you'll like some of my others. Check them out at
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