Materials Needed

• 10 long nails (the ones with flat, round heads)
• Hammer
• Small block of wood (5" x 5" will work)

Procedures

1. Hammer one of the nails into the small block of wood so that it stays put and the rest is standing straight up. Don’t hammer the nail in all the way.
2. Lay one of the nails on a table. Then lay seven of the remaining nails across it.
3. Lay the ninth nail on top.
4. Carefully hold the ends of the bottom nail (the first one you laid down) and slowly lift. As you lift, the seven nails you laid across the bottom one should slide closer together and their heads should lock against the top (ninth) nail.
5. You can now easily balance all nine nails on top of the tenth.

Why Does It Work?

Honestly, the nine nails aren’t really balancing on the tenth – they’re actually hanging! How can this be, you ask? It all deals with the center of gravity of the nine nails. The center of gravity depends on how the weight of an object is distributed. An object is balancing if its center of gravity is above its point(s) of support. When you stand, you’re balancing because your center of gravity is above your feet. If an object’s center of gravity is below the point of support, it is hanging

So, have another look at the arrangement of the "balanced" nails. Can you see most of them are hanging well below the head of the tenth nail? The center of gravity in this arrangement is well below the point of support. It really isn’t a balancing trick after all. The nails are hanging. Pretty cool, huh?