Think you can make a steel needle float on water? If you’re like most people–and think not–then we’ll prove to you it can be done simply with your own hands.
You will need: cooking oil (or other fat). If you’re doing the experiment as a magic trick, apply oil to your palms unnoticed.
Now place the needles on your open hands.
Rub your hands together–very carefully, so as to avoid poking yourself. If you’re performing for an audience, you can say some “magic words” at this point. But the main purpose here is to coat the needles with oil.
Now gently place the needle on the water’s surface.
Amazing! The needle doesn’t sink!
To prove your magic abilities, make the second needle float next to the first. But why, in fact, do the needles not sink? Metal is much heavier than water, after all, and if the needles found themselves underwater, they certainly wouldn’t float to the surface. But our needles won’t sink because they are actually being held up by the water. If you look very closely, you’ll see a slight concavity in the surface of the water next to the needle. The needles, being coated in oil, aren’t moistened by the water, and are instead lying on top of the water’s surface. The surface tension of the water is strong enough to resist breakage by the weight of the needle, and its tendency to maintain a smooth surface means that it is actually “pushing” the needle out of the water while at the same time being slightly pressed down by it.