Balancing Nails Balance all of the nails on the head of a single nail. email to friend
print this page

You'll start by hammering one of the nails into the center of the block of wood.  It's a good idea to measure and pre-drill the hole to avoid splitting the wooden block.

Place the wood block flat on a desk or table. The challenge is to balance all of the nails on the standing nail in the wooden block. To win the challenge, none of the eleven nails may touch the wood block, the desk or table, or anything else that might help hold them up. No additional equipment other than the wood block and the nails may be used.

In the large-scale version, have a volunteer hold one of the large nails while you attempt to balance the other eleven nails on the head of the single nail. Here's a word of advice... start with the small-scale version and work your way up!

How does it work?

The trick to balancing the nails has to do with their "center of gravity" or balancing point. Lay one nail on a flat surface and place other nails across this nail, head to head as shown in the photograph. Finally, place another nail on top of this assembly, head to tail with the second nail. Carefully pick up the assembly and balance it on the upright nail.

Gravity pulls any object down as if all of its weight were concentrated at one point called the "center of gravity." Objects fall over when their center of gravity is not supported. For symmetrical objects like a ball or a meter stick, the center of gravity is exactly in the middle of the object. For objects that are not symmetrical like a baseball bat, the center of gravity is closer to the heavier end.

The stability of the nails depends on their center of gravity being right at or directly below the point where they rest on the bottom nail. Add too many nails to the left or right and they become unstable and fall off.

Slowly remove one nail at a time. How many nails could you remove before the system collapsed? Which nails were necessary for the system to remain in balance?

This "scientific" puzzle is trickier than it looks. The best way to solve the puzzle is to think of an idea and then try it out. Even if it doesn't work, you might think of another idea at the same time. The key is not to get frustrated and give up. Keep trying. You might even have to sleep on an idea and come back to it the next day. You might even want to share your ideas with someone else to see if they have a different approach to solving the problem. This process is known as "brainstorming" and is very useful when trying to solve a problem.

Additional Info

The large-scale version was developed for the television show. The demonstration is performed in the exact same manner, but everything is larger. The trickiest part is working with your volunteer to make sure they can balance the nails once they're positioned on the head of the single nail. Practice makes perfect.