Raven
Well-known member
Based on recent conversations regarding wind speed and its relationship to force, energy, power, etc, I did a few calculations that I thought would help explain this relationship for those who may want to know why the strength of the wind seems to increase so dramatically with speed. I also thought it best to begin a new thread with this. If you read to the end you may be surprised.
Background Info:
-Many people seem to know that when the speed of the wind doubles, something increases by 4 (the strength, the force, the energy, the power, etc) but this is where the details get murky. Here are the differences:
-For FORCE, look to the following few posts and their included links for a very thorough explanation that is much better than I can give.
What follows shows an explanation and then series of numbers meant to show the relationship of wind speed to wind power and to show the added effect of the increasing mass of the air hitting a person as the wind speed picks up.
-ENERGY is the ability to do work. Kinetic energy is the energy that moving things have. Things like moving trucks on highways, water moving downstream, moving air masses (wind) all have kinetic energy. This is where the 4x thing comes in. The KE depends on two things, the mass and the speed of the object (KE = 1/2mvv). But the speed gets multiplied twice, so as the speed doubles, the energy increases by 4 times! Here's an example from the football field. If you have the option of getting hit by the small guy (150 lbs) moving fast at 12 mph or the big guy (300 lbs) moving slow at 6 mph, take the big guy, because the small one has much more energy and will hurt more.
-Don't skip this part. In the above example, people always remember the 4 times thing but there's a more subtle, VERY important consideration. Mass of the air is in that formula. As the wind speed doubles, there is twice the mass of air molecules hitting your body per second. So, when the wind speed doubles, the energy actually increases by a factor of 8 times!
-POWER is energy used per second. If you walk up a flight of stairs you use energy. If you run up the same flight of stairs you use exactly the same energy but more power since it is used in less time. Some battery operated tools use up the battery faster because they take more power. A tool using less power will use the same battery up over a longer time period.
I did some calculations for wind speeds that I thought would make sense for people to see this. I've attached a PDF which includes the wind speeds 45, 90, 180, and 231 mph. For each speed I calculated power of the wind at that speed that might be felt buy a typical person and the results show how dramatic it is.
Results:
1. A Gale Force Wind of 45 mph will have entire trees swaying wildly and twigs breaking off. This is what we all tend to call "like 70-80 mph out there!" This is a STRONG wind. (Power = 5700 J/s)
2. Double this to 90 mph, a strong category 1 hurricane (nearly 2), and the power goes up by a factor of 8 to 45,000 J/s. In this wind, buildings can receive severe damage. People buckle down for these storms. To put the wind of 2/16/2015 in perspective, the date of Kate Matrosova's death, the average wind speed on Mount Washington that day was 91.2 mph, nearly a category 2 hurricane with 8 times the full power of a gale force wind.
3. Double this to 180 mph, a strong Category 5 hurricane and the most intense storms seen on earth. Hurricane Andrew at sea, when it was a 5, did not sustain these speeds. Wilma and Rita are the only Atlantic storms so far this century to have sustained these speeds for more than 60 s. Compared to a Category 1 storm, this is 8 times more powerful and 64 times more powerful than a gale force wind. Buildings have blown off Mount Washington in these winds. (P = 366,000 J/s)
4. 231 mph. 133 times the power of a gale force wind. Armageddon. (P = 760,000 J/s)
I hope this is somehow helpful in understanding the power of the wind.
Background Info:
-Many people seem to know that when the speed of the wind doubles, something increases by 4 (the strength, the force, the energy, the power, etc) but this is where the details get murky. Here are the differences:
-For FORCE, look to the following few posts and their included links for a very thorough explanation that is much better than I can give.
What follows shows an explanation and then series of numbers meant to show the relationship of wind speed to wind power and to show the added effect of the increasing mass of the air hitting a person as the wind speed picks up.
-ENERGY is the ability to do work. Kinetic energy is the energy that moving things have. Things like moving trucks on highways, water moving downstream, moving air masses (wind) all have kinetic energy. This is where the 4x thing comes in. The KE depends on two things, the mass and the speed of the object (KE = 1/2mvv). But the speed gets multiplied twice, so as the speed doubles, the energy increases by 4 times! Here's an example from the football field. If you have the option of getting hit by the small guy (150 lbs) moving fast at 12 mph or the big guy (300 lbs) moving slow at 6 mph, take the big guy, because the small one has much more energy and will hurt more.
-Don't skip this part. In the above example, people always remember the 4 times thing but there's a more subtle, VERY important consideration. Mass of the air is in that formula. As the wind speed doubles, there is twice the mass of air molecules hitting your body per second. So, when the wind speed doubles, the energy actually increases by a factor of 8 times!
-POWER is energy used per second. If you walk up a flight of stairs you use energy. If you run up the same flight of stairs you use exactly the same energy but more power since it is used in less time. Some battery operated tools use up the battery faster because they take more power. A tool using less power will use the same battery up over a longer time period.
I did some calculations for wind speeds that I thought would make sense for people to see this. I've attached a PDF which includes the wind speeds 45, 90, 180, and 231 mph. For each speed I calculated power of the wind at that speed that might be felt buy a typical person and the results show how dramatic it is.
Results:
1. A Gale Force Wind of 45 mph will have entire trees swaying wildly and twigs breaking off. This is what we all tend to call "like 70-80 mph out there!" This is a STRONG wind. (Power = 5700 J/s)
2. Double this to 90 mph, a strong category 1 hurricane (nearly 2), and the power goes up by a factor of 8 to 45,000 J/s. In this wind, buildings can receive severe damage. People buckle down for these storms. To put the wind of 2/16/2015 in perspective, the date of Kate Matrosova's death, the average wind speed on Mount Washington that day was 91.2 mph, nearly a category 2 hurricane with 8 times the full power of a gale force wind.
3. Double this to 180 mph, a strong Category 5 hurricane and the most intense storms seen on earth. Hurricane Andrew at sea, when it was a 5, did not sustain these speeds. Wilma and Rita are the only Atlantic storms so far this century to have sustained these speeds for more than 60 s. Compared to a Category 1 storm, this is 8 times more powerful and 64 times more powerful than a gale force wind. Buildings have blown off Mount Washington in these winds. (P = 366,000 J/s)
4. 231 mph. 133 times the power of a gale force wind. Armageddon. (P = 760,000 J/s)
I hope this is somehow helpful in understanding the power of the wind.
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