Why Does Cold Air Fall and Warm Air Rise?

cold air falls and warm air rises. Why? Discuss!

Many of us experience the effects of falling cold air and rising warm air on a regular basis. It is happening all the time in the air above and around us and is one of the components in our weather systems. You may notice that when there is no heating or air conditioning operating in your house, the rooms upstairs are slightly warmer than those downstairs. Another example is the hot air balloon that works precisely to this principle. By heating the air inside the balloon, the craft will be lighter than the surrounding air and will rise. This is actually the result of cold air gushing downwards around the balloon at the same time as it is rising.

So why does cold air fall? That is simple: it is heavier than warm air. And why is it heavier? That is slightly less simple, but only slightly. As with any gas, the air (a generic term for the mixture of the gasses in our atmosphere), contains molecules that move (or agitate). This movement (or agitation) is greater as the temperature rises. The molecules move in ever greater orbits, taking up more space. This causes the mass of the air to expand. Although the total mass of a lump of air has not changed, the mass is more spread out and so any given cubic area of it will be lighter. An analogy is found with popcorn. A half pound of popcorn before being popped may fit into a cup. After popping, the same corn would fill a large saucepan. Its total weight will be more or less the same half pound that it always was, but if you filled up the original cup with the popped corn, it would weigh less than the unpopped corn as the rest of it would no longer fit into the cup. Expanding hot air is similar. A cup of cold air would weigh more than a cup of hot air.

As we are playing the why game, let's continue. Why do the molecules move about more when it is warmer? They absorb energy through electro-magnetic waves that smash into the molecules. In short, this is energy transfer by radiation. So we have a collection (several trillion, lets say) of molecules that are very agitated and another collection which are far less agitated. The agitated collection is spread out and thus light. The collection that are less agitated is heavier. The heavier stuff falls downwards, while the light stuff rises.

As well as being the main process behind hot air balloons, the movement of air according to its temperature is a critical factor with the weather. forecasters must ensure that these movements are factored into their modelling systems in order to produce a decent weather forecast. Air conditioning designers and must also take these factors into account as must architects. In order to preserve valuable heat, warm air must be prevented from escaping through the top of a building. As well as conserving heat, the movement of colder air downwards must also be considered when designing refrigerators and refrigeration systems.

If you have a few minutes, try this experiment. Firstly make sure nothing has been put into your refrigerator for at least 2 hours. Then, leave a thermometer inside the refrigerator, making sure it is placed at the bottom and then close the door. After 10 minutes, open the door and straight away and note the reading on the thermometer. Then place the thermometer on the top shelf and close the door. After 10 minutes, take the reading as soon as you open the door. You will notice a difference - perhaps as much as 1 to 2 degrees. This may not be such a big issue for us at home most of the time. For commercial kitchens, however, this difference maybe critical when ensuring food is kept at an optimum temperature. Commercial fridges are often fitted with a fan that evens out the colder and warmer air, thus negating the tendency for cold air to fall and warmer air to rise.

If you take large freezer stores - the ones that hold thousands of boxes of stock - the movement of air around the facility is an extremely important factor. The fans that blow frozen air into the store are always situated near to the ceiling, allowing it to diffuse downwards. Eventually, of course, the goods in the freezer store will need to be taken out and moved to another location, typically loaded onto a truck. If frozen goods are loaded onto a frozen truck this is no problem. Occasionally though, only a small quantity of frozen goods may be needed and the use of a large truck whose temperature is set at a frozen temperature would be wasteful if only a few boxes were being despatched. This is where insulated pallet shrouds or roll cage covers come into play. These enclose the pallet or roll cage, protecting frozen goods for up to 8 hours within an ambient environment (they also protect ambient goods such bakery products and bananas in a chilled or frozen environment). When a roll cage is used, the insulated roll cage cover works at its best when the cage is full of products. When it is half full then - you guessed it - the cold air falls to the bottom. This is fine at first (assuming the goods are in the bottom half), but after a while the warmer air that has risen to the top will start to affect the top layer of goods. This is where a temperature insulated divider must be used to make a seal and protect the goods in the half full roll cage.

So now you know the whys and hows of cold and warm air and now you also know why your feet get cold in winter!

Vernon Stent is the content writer for 5es.co.uk, where you can purchase or rent roll cage insulation covers and dividers and pallet covers.

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Signs of a Leaky Basement

Some signs of a leaky basement are very obvious and others are not so obvious. Of course the most obvious sign of water leaking is water everywhere or pools of water on the floor! You might also actually hear the water dripping or staring at big ugly brown stains spreading across your walls. Sometimes you can even smell the water particularly if it is tainted by sewage or tainted by pesticides. Sometimes leaky water also has the heavy musky smell of fresh soil as often water leaking through a bad basement foundation will also be carrying a lot of silt with it.

There are also lots of other clues that you have a leaky basement. One sign of a leaky basement that is often just interpreted as aging or fading is the presence of efflorescence. Efflorescence is a deposit of a thin white film on your wall. It is the residue left by water that contains minerals and other effluvia from the soil.

Dampness is of course a big sign that you have a leaky basement but you should also look for other signs such as rusting nails or metal fixtures, rotting wood near the floor level, rusted metal feet on appliances, lifted floor tiles and peeling paint. All of these signs are not necessarily indicative of big disaster however it is possibly an indication that your home is suffering some kind of leakage during a rainy or wet season.

Sometimes the leaky basement is not due to some sort of vulnerability in your basement foundation. Sometimes it is caused by breaks in your water supply lines or pipes. Even a small seam or crack in a pipe can cause a big pool of water to form on your basement floor. Yet another big culprit is sinks and toilets that constantly drip as the result of a loose joint or loose pipe. Often this type of water collects beneath a cupboard in which the actual plumbing works are concealed.

There is almost always a little bit of leakage around the places where pipes enter the home. This is because of condensation on the pipes forming dew. To prevent this type of water leaking into your house (and first make sure that it is not the pipe itself that is leaking or your efforts will be futile) you can patch it with a waterproof concrete patch. Keep in mind that this will not prevent the water from forming from behind the walls. The only thing that might prevent that is the installation of a dehumidifier. Dehumidifiers can be an important tool in your battle against basement moisture and molds but not if the moisture is actually due to water seepage as opposed to water condensation.

There is a very easy way to determine if water on your basement walls is due to condensation or seepage. Simply tape a piece of aluminum foil to your basement wall. After a few days inspect its surfaces. If there is moisture on the inside surface that was touching the wall then you are dealing with a leak. If moisture forms on the aluminum foil side that is facing out from the wall then the problem is condensation and can easily be dealt with by a dehumidifier.

The good news is that condensation is a lot easier to manage than leaking water. Although it is persistent the excess humidity is manageable. Exposure to sunlight and wind can help dry out a basement that is dripping with condensation. It is also a good idea to keep basement windows closed if you live in a climate that is overly humid or that has a heavy rainy season.

Learn the causes of a wet basement and how to avoid them at Waterproof a Basement.

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