Bet your friend that you can pick up two sheets of newspaper with a 12-inch ruler but that he or she is too weak to do it. When your friend says "No way," set up and do this trick.
What You Need:
~ 2 wooden 12-inch rulers (or 2 wooden paint stirrers)
~ 4 sheets of newspaper
~ kitchen table
What You Do:
1. Put the rulers on opposite sides of the table so about 3 inches of each ruler sticks out over the edge of the table.
2. On your friend's side of the table,
completely unfold 2 sheets of newspaper
and place them over the ruler. Arrange
the paper so the long bottom edge is
even with the edge of the table and
the ruler runs along the middle fold.
Smooth the paper on the table with
your hands.
3. For your side of the table, fold the
newspaper along the long vertical
middle crease, then fold in half
horizontally, then one more time
vertically. You should have a folded
newspaper that's one-eighth the size
of the unfolded sheets. Lay the
folded paper over the ruler.
4. On the count of three, both you and your friend should hit the end of the ruler that sticks out with your fist.
What Will Happen:
Your folded paper will fly into the air. Your friend's unfolded paper will stay on the table; it might rip or the ruler (or stirrer) may break.
Why It Happens:
Are you really stronger than your friend? Nope, but you're a bit smarter. The weight of the paper is the same whether it's folded or not, but the weight of what's on top of it is not. What's on top? Air. The air around us has weight and that weight presses down on everything. Things that have a larger surface area, like the unfolded paper, are pressed down more than things with a smaller surface area, like the folded paper. In fact, the unfolded paper with eight times the surface area as the folded paper has eight times as much air pressure on it.
Try It:
On the surface of Earth, air pressure is about 15 pounds per square inch. Measure in inches the long and short sides of the unfolded and folded papers. Multiply to get the surface area of each. Multiply each of those areas by 15 pounds per square inch. Do your results surprise you?
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