Yesterday’s Problem:
Fill a glass with water completely up to the rim. Then slip a penny into the glass. The water will not overflow with just one additional penny inside. Approximately how many pennies can you slip into the glass before the water spills over the edge?
Try it out. See what you get. This is something fun to do on New Year’s Day, eh?
Answer:
The precise answer will vary of course depending on circumstances, but you can put as many as 52 pennies into the glass before it overflows.
Water has a very high surface tension. It behaves much like flexible skin which pills inward and always resists breaking.
A glass of water can develop a huge bulge before it flows over the edge of the glass. Surface tension can also support the weight of light objects. For example, if you place a razor blade flat against the surface of the water, the razor blade will actually float on top of the water even though you would expect it to sink down to the bottom because of its weight.
Surface tension of the water holds up the razor blade. It is certainly not held up by the buoyancy of the razor blade which is very dense.
How many pennies did you successfully put into your glass?
Today’s Problem:
You are celebrating today the birthday of your two year old niece. Her birthday cake has two candles proudly place on top. When your niece attempts to blow out the two candles, she blows between them (instead of blowing them out). What happens to the flame of the candles? Do the flames move outward, inward or simply flicker?