Energy Density

Hot-air balloons float because the air inside the balloon is less dense than the outside air Click on image for full size (116K JPEG) A tornado is the most destructive natural storm. You might think that this also means that tornadoes are the strongest storms; that's not the case. In fact, a thunderstorm which produces a tornado can have 40,000 times more energy than a tornado! Then why are tornadoes so much more destructive than thunderstorms? Tornadoes have a greater energy density than thunderstorms. They don't have as much energy but the energy they do have is packed into smaller spaces. Another way of thinking about this is with rocks and feathers. A bag of feathers might outweigh a rock, but put them both in water and the feathers will float while the rock sinks because the feathers are less dense. Tornadoes are so destructive because they strike a very small area.

Energy Density

Hot-air balloons float because the air inside the balloon is less dense than the outside air Click on image for full size (116K JPEG) A tornado is the most intense force in nature. That doesn't mean it's the most powerful. In fact, a thunderstorm can be 40,000 times more powerful than a tornado. Then why aren't thunderstorms as dangerous as tornadoes? The answer lies in each storm's energy density. A tornado may not have nearly as much energy as a thunderstorm, but the energy in the tornado is concentrated into a much smaller area. Imagine you have a hose and are watering a yard. You can spray five gallons of water over the whole yard and not really notice it. If you were to spray a couple gallons in one small section, you would probably flood and possibly start to erode it. That's because the water was very concentrated, like the energy in a tornado.

Energy Density

Hot-air balloons float because the air inside the balloon is less dense than the outside air Click on image for full size (116K JPEG) A tornado is the most destructive force in nature; that doesn't mean it has the most energy. Thunderstorms which produce tornadoes can have 40,000 times as much energy as a tornado! Tornadoes are so destructive because they have a higher energy density than thunderstorms; the energy is concentrated in a small area while the energy in a thunderstorm is spread-out over a much greater area. Energy and energy density can be compared to weight and force. Energy density is energy per unit volume and force is weight per unit area. If a 100 pound person in flat shoes stepped on your foot, you'd feel it. If the same person stepped on your foot while wearing very narrow high-heels, you might end up with a broken toe. That's because the person's weight is concentrated in a small area. The same holds with tornadoes. They may not have as much total energy as thunderstorms, but the energy they do have is concentrated in a very small area. So small, in fact, that tornadoes have destroyed houses while not damaging the neighbors.

Last modified prior to September, 2000 by the Windows Team

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