The Mpemba effect

first_imgOn the aspect of repeatability, Walker reported that whilst most of his results were repeatable, he sometimes observe large variations in his results and said “I have not been able to resolve the controversy”. Having boiled some milk for making ice cream, his class were told to let the mixture cool before putting it in the refrigerator. Mpemba, however was anxious of ensuring himself a space so put his mixture in straight away. I said Mpemba re-discovered this; having mentioned this “Mpemba Effect” in one of their articles, the “New Scientist” was subsequently flooded with anecdotes from all over the world of only the hot water pipes freezing during a short cold snap, ice-rink operators preferring to use hot water and so on. Osborn and Mpemba published these results in a journal called “Physics Education”, coincidentally the same year that George Kell at the National Research Council of Canada in Ottawa reported the same phenomenon that year in the “American Journal of Physics”. In a subsequent year at high school Mpemba was taught about Newton’s law of cooling in science: the rate at which a body cools is proportional to the temperature difference between that body and its surroundings:…which leads to the solution… Any set of cooling curves plotted from such a function will never cross, no matter what the initial starting temperature. So a curve which starts at a higher temperature will never undercut a curve starting at a lower temperature and will therefore always take longer to cool. Varying the parameter k on the other hand could well cause graphs to cross. But this parameter is determined from some initial conditions, if both systems are not identical in such things as geometry or arrangement, with the exception of starting temperature, then it is hardly appropriate to compare cooling times for different initial temperatures. The lab-assistant reported the hot water had frozen first, but not to worry, “I’ll keep on repeating the experiment until we get the right result.” After several attempts it seemed Mpemba was right – hot water would freeze faster than cold water. However, Mpemba was undeterred by a theory which didn’t seem to support his observations: he’d asked a friend who sold ice cream in a nearby town who told him he routinely used hot mixtures because they froze more quickly. Still persisting with this, in 1969 a visiting academic from University College in the capital called Dr Osborne came to visit Mpemba’s school and he jumped at the opportunity to quiz him about this apparent violation of Newton’s Law. Thankfully he didn’t dismiss it outright, and upon returning to Dar es Salaam, he instructed a lab-assistant to carry out an experiment to see if hot water would freeze more quickly than cold water. Publish or perish He came away with the simple observation that “hot liquids freeze faster than cold liquids”.His science teacher told him this was impossible and he must have got mixed up. So why exactly is this impossible? So this clearly wasn’t unheard of. Mpemba was a secondary school student in Tanzania in 1963 who had the fortune of re-discovering some interesting physics during one of his cookery lessons. Surely the validity of this effect can be deduced by carrying out experiments – however this has proved surprisingly difficult. The Mpemba effect is only observed under certain conditions – there are clearly many factors which could affect how quickly water cools such as the geometry of the container, the volume of water and the temperature of the refrigerator. In 1977, Jearl Walker published results in the “Scientific American” whereby the time to freeze was measured against the initial temperature for a variety of containers. His results showed two things. Firstly where negative gradients occur, water at an initially higher temperature appeared to be freezing more quickly. Secondly, this is by no means a universal effect, since most of the curves showed very little (if any) in the way of negative gradients. The other students waited and put their mixtures in later, after they’d cooled down. Having noted the time his ice cream entered the freezer compared with the rest of his class, Mpemba realised his mixture had frozen significantly faster than everyone else’s. So assuming both Newton and Mpemba are correct – how do we understand what is going on here? Can we somehow reconcile these two arguments? CHECK BACK NEXT WEEK TO FIND OUT…by Will Frasslast_img read more

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O.C. Board of Realtors Food Drive in Full Swing to Help the Needy

first_imgDottie Cianci, coordinator of the Ecumenical Council’s Food Cupboard, and Dave Carter, former president of the Ocean City Board of Realtors, inspect donated items during a food drive. By Donald WittkowskiMultimillion-dollar beachfront homes, trendy downtown boutiques and upscale sailboats traversing the waterways provide a decidedly affluent backdrop in Ocean City.But there are lesser-known parts of town where people are suffering, where poverty and hunger exist, said Gloria Votta, chairwoman of the Community Services Committee for the Ocean City Board of Realtors.“It would surprise people. It’s very surprising,” Votta said of the city’s poor population.For those people, the Board of Realtors is lending a helping hand through its annual community food drive in partnership with the Ocean City Ecumenical Council, an association of local churches that helps needy families.Food is given away for free to Ocean City residents by the Ecumenical Council’s Food Cupboard at St. Peter’s United Methodist Church, Eighth Street and Central Avenue. The hours are 1-3 p.m. Monday through Friday.Dottie Cianci, coordinator of the Food Cupboard, said more than 100 families will benefit from the food drive. It will help all demographic groups, including people who live in low-income housing, senior citizens and homebound residents. The Food Cupboard makes deliveries to senior citizens and homebound residents.“There are some people who simply can’t get out. I’m just so proud of this, because we just started it,” Cianci said of the delivery service.In addition to food, the Board of Realtors is also collecting household items, including detergent, paper products, soap and toothpaste.Originally scheduled to end on Feb. 28, the “Food is Love” drive has been extended through March 15 to give the Board of Realtors more time to collect items donated by the public. Votta said the food drive underscores the level of compassion the community has for needy families and senior citizens.“There is nothing this community will not pull together to do,” she said. “I think it’s one of the best places to live as far as a caring community is concerned.”Now in its seventh year, the food drive is among a series of charitable events organized by the Board of Realtors. The organization also holds clothing drives and a Toys for Tots campaign throughout the year.Food donations may be dropped off at the Board of Realtors office at 405 22nd Street. To arrange for food pickups, people may call the office at (609) 399-0128. The office is open Monday through Friday from 9 a.m. to 5 p.m.In addition to nonperishable food donations, the board is also seeking household items, including liquid laundry detergent, dish detergent, paper towels, toilet paper, shampoo, deodorant, soap and toothpaste.Dave Carter, president of the Board of Realtors, noted that some people choose to donate cash, which in turn is used to buy gift cards at local grocery stores. So far, about $500 in cash has been donated for the food drive, he said.Already, dozens and dozens of food items and household goods have been collected at the Board of Realtors office. The board’s conference room has been turned into a makeshift pantry – crowded with cans of soup, microwaveable dinners, canned goods, cereal and jars of peanut butter and jelly.“What you see here is only part of it. There are a lot of boxes we still have to pick up,” Carter said.Donations may be dropped off at the Board of Realtors office at 405 22nd Street.last_img read more

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Police identify body found at Round Lake

first_imgA man found dead at 7:10 a.m. Thursday in Lacamas Park at Round Lake in Camas is believed to have committed suicide, reports the Camas Police Department.Carlos E. Slaughter, 22, died of asphyxia, according to an autopsy by the Clark County Medical Examiner’s Office.An investigation by Camas police is ongoing.last_img

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