My PBL Project

Materials:

A block of wood

12 identical nails with heads(use 10 penny size or larger)

Hammer

Procedure:

Start by hammering one of the nails into the center of the block of wood. The nail does not have to be perfectly centered, but the closer it is to center, the better.

Place the wood block flat on a desk or table and try to balance the remaining 11 nails on the head of the standing nail.

Lay one nail flat on the table.

Arrange the first of the remaining nails so that the nail head is propped up by the nail laying flat on the table.

The next nail should lay in the opposite direction. The two nail heads should only be separated by the width of the nail that is laying flat on the table.

Continue laying the nails in alternating directions until you achieve the pattern shown at right.

The final nail should lay in the opposite direction as the nail laying flat on the table. This final nail will rest nicely between the heads of the propped nails. Again, refer to the picture at right for how this should look.

Carefully lift the nails by the nails on the top and bottom of the pile.

Scientific Principle:

The trick to balancing the nails has to do with their "center of gravity" or balancing point. Gravity pulls an 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.