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| Sunday, 4 September 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Meals in a minute!
A microwave oven uses microwaves to heat food. Microwaves are radio waves. In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz). Radio waves in this frequency range have an interesting property: they are absorbed by water, fats and sugars. When they are absorbed, they are converted directly into atomic motion - heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven. You might have heard that microwave ovens cook food "from the inside out". What does that mean? Here's an explanation to help make sense of microwave cooking. Let's say you want to bake a cake in a conventional oven. Normally you would bake a cake at around 350 degrees F, but let's say you accidentally set the oven at 600 degrees instead of 350. What is going to happen is that the outside of the cake will burn before the inside even gets warm. In a conventional oven, the heat has to migrate (by conduction) from the outside of the food toward the middle. You also have dry, hot air on the outside of the food evaporating moisture. So the outside can be crispy and brown (e.g. bread forms a crust) while the inside is moist. In microwave cooking, the radio waves penetrate the food and "excite" water and fat molecules pretty much evenly throughout the food. There is no "heat having to migrate toward the interior by conduction". There is heat everywhere all at once because the molecules are all excited together. There are limits of course. Radio waves penetrate unevenly in thick pieces of food (they don't make it all the way to the middle), and there are also "hot spots" caused by wave interference. The whole heating process is different because you are "exciting atoms" rather than "conducting heat". In a microwave oven, the air in the oven is at room temperture, so there is no way to form a crust. That is why certain foods come with a little cardboard or foil sleeve. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy as it would in a conventional oven. ############# Where is your Centre of Gravity?
How does this affect us? Well, where you put your C.o.G. can decide whether your weight is on your arms or your legs. For example, your weight is on your legs if the foot you are using is directly underneath your centre of gravity, or you have one foot on each side of it. This is good. Your weight is on your arms if both your feet are to one side of your centre of gravity. This will tire your arms out. Hence, the simple rule about keeping your body close to the climbing wall: if you do this, your weight is on your feet, but if you lean out, your weight is on your arms.Back to the important bit. If your weight is on your legs, you can move your hands from one hold to the next slowly and calmly, without having to grab for the hold (and probably miss). This is called being in balance. It's good. It will work wonders for your style, energy and grace. Gravity is one of the forces that control how the physical world works. It keeps trying to pull things towards the centre of the Earth. Without realising it, we've learnt to outsmart gravity. Otherwise, we would fall over every time we took a step. We "outsmart"
gravity by positioning our centre of gravity, an imaginary spot in the
middle of the stomach about 8 cm below the belly button. As long as we
keep the centre of gravity over our feet, we can stand and walk. |
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| News | Business | Features
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| Politics | Produced by Lake House |
The microwave oven is one of the great inventions of the 20th century.
Although they may still be a relatively novel concept in Sri Lanka,
millions of homes in developed countries use them. Microwave ovens are
popular because they cook food in an amazingly short amount of time. They
are also extremely efficient in their use of electricity because a
microwave oven heats only the food - nothing else. Today we will discuss
the mystery behind the magic of "meals in a minute" with microwave
cooking. 
Ever wondered what your Centre of Gravity is? Your Centre of Gravity (C.o.G.)
is roughly the middle point of your body. It is somewhere in your abdomen,
and the weight of your entire body is acting from this point. 
