Q: Why does hot water appear to freeze faster than cold water? ………………….Bob, Nashua
A: My first experience with that phenomenon was watching someone put hot water into their ice trays and slip them into the freezer. My natural curiosity asked why, and the answer was, “because it freezes faster.”
Apparently your question is on the mind of many at the moment since the Royal Society of Chemistry in the UK has offered 1000 lbs. for “the most creative explanation” of the phenomena known as the Mpemba effect.
Hot water can in fact freeze faster than cold water in a large range of experimental conditions. Although it appears counterintuitive, many scientists as far back as Aristotle, Bacon and Descartes (17th century) have reported it. The effect is today named after a Tanzanian schoolboy who noticed his milk froze sooner than that of his schoolmates because he did not wait to cool the milk before freezing it. When he asked a visiting professor about it the professor and his assistant repeated the experiment and later published the results in a physics journal.
There have been several different suggested reasons for this effect, ranging from evaporation, dissolving gasses, convection and the surroundings. There are a lot of variables to consider, however, so no definitive reason has been found, any one of or a combination of these can conceivably change the outcome.
Some think that since the hot water evaporates there is less water left to freeze so it freezes sooner. Others believe that when the gasses in the water are heated they escape and it changes the properties of the water and allows the water to freeze faster. Still others point to the different levels of temperature in the hotter water as it cools causing convection currents which speed up the process. Until experiments can be done that control all aspects of the phenomena there will be no final answer.
Q: Are all male birds species more colorful and the females less so?
A: The males of most bird species might be the pretty colorful ones, but it is the female who does the choosing. The color of the birds suits the function they have. If the female bird of the species is the one who sits on the eggs and protects the young than she will blend in better with the surroundings and not get eaten. If the species is polyandry then the female will be the more colorful one and have several mates and nests. This is rare in North America but there are three species that behave this way. The female Red Phalarope, for example, is bigger and more colorful than the male and plays no role in incubating or caring for the young. She spends a week or so with one male, courting it and laying eggs in the nest until it is full. Then she begins to search for another mate to repeat the process all during the mating season. She then begins migrating south long before the eggs have been hatched by the dedicated males. Spotted Sandpipers and Belted Kingfisher females also have beautiful colors to attract mates.
Ask Madalyn welcomes your questions about anything that interest you.
- Wednesday, 04 July 2012
- Posted in Categories: : Ask Madalyn