Tuesday, February 2, 2010

Energy - the Beginning.

Energy realized.

Typically when reading physics chemistry books one will run across definitions of energy that are less then useful when applied to real live experience. Hopefully this brief discussion over the next few blog posts will hopefully bring the idea of energy into a more useful format.

Typically energy is defined as “the ability to do work.” Although correct this definition is somewhat abstract. Another more useful definition is “anything that can be turned into heat.” Either way although these definitions describe energy they do not explain its nature or make it useful.

So how then does energy work?

Often the confusion begins with the litany of terms used to define energy. So without getting into all of them and their conversion factors too quickly we will analyze one of them, the Calorie (this is the food Calorie as apposed to the lower case c. calorie often found in physics or chemistry that is equal to 1/1000 of a food Calorie).

The Calorie is simply the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. So as a practical example. If one was to take one gram of gasoline which is equivalent to 10 Calories, one could burn the one gram of gasoline under a one kilogram tub of water, and in a isolated environment where no energy or heat was lost to the air or containers – an ideal system – once the one gram of gasoline was burned completely it would have raised the temperature of the water by one degree Celsius. (This is not easy process to get 100% accurate since the beginning water temperature affects the outcome, but it is the method to define a Calorie).

Now that said the reality is that info is still not very useful in real life. But this data below is.

PETN or popcorn?..Special Ops got it all wrong!

Now that we understand a little about the nature of a Calorie unit of energy, how is that information useful – or at least interesting?

To begin lets take two substances and compare their Caloric energy and application. First we have the average buttered popcorn. The average buttered popcorn you can pickup to munch on while watching your favorite flick has 5 Calories per gram. Although the majority of the Calories are in the butter it is still interesting to make the comparison to PETN a.k.a. Plastic Explosives.

PETN (PantaErythritol TetraNitrate) on average contains approximately 1 Calorie per gram. That means strictly speaking buttered popcorn contains 5 times more energy then plastic explosives, which is one of the most powerful high explosives known. So then why do Military Special Ops or demolition teams pack their rucksack with PETN when they could carry 5 times less weight in popcorn and get the same energy output? The difference is in the nature of how quickly the Caloric energy can be converted into heat, or as defined at the beginning how quickly the energy can do work. With PETN the detonation velocity is 8500 meters per second when pressed in a steel tube, it detonates at a temperature of approximately 4230 degrees Celsius. This rapid detonation and high heat create a massive volume of gasses suddenly. Because the gasses it produces take up a greater volume then the surrounding air prior to the detonation, the rapid introduction of these gasses to the surrounding environment cause everything to be suddenly and violently pushed out of the way including the air itself. Since the air itself is pushed a wave of compressed or “pushed” air travels out quickly creating a “shock wave” of high pressure air that further destroys or disturbs anything in its path. PETN has the ability to rapidly detonate because of the nature of its molecular structure.

On the other hand, buttered popcorn does not intrinsically have the ability to suddenly turn its Caloric energy into heat and work. It takes a slower process such as burning or the chemical process in our body’s called metabolism to extract the energy / work / heat. So although it has a higher Caloric count or contains more energy then PETN, the nature of the substance does not allow it to be useful in blowing things up. (although as a side note if one was to eat popcorn and set at the task of demolishing something with a sledge hammer as apposed to detonating it with PETN…the conversion of calories to energy to the work of demolition would have a similar outcome)

Next Week, Why the Gasoline addiction?

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