## Wind Force

Perhaps you have wondered why a 40 kt wind does little or no damage, while an 80 kt wind, only twice as fast, can snap trees off at the trunk, shatter window panes, and send large objects flying through the air. Moving air produces measurable forces against objects that get in the way. This force increases much more rapidly than the speed in knots. This is why incredible things happen in severe hurricanes and in tornadoes. The power of the wind in a tornado can be thousands of times the power of a late-autumn gale that rattles the windows and strips the last of the leaves from the trees.

When a strong wind blows against a building, force is produced directly against the wall or walls facing most nearly into the wind. This is positive force. There are also other forces generated by winds blowing around an object. As the air flows over the roof, the pressure above the surface goes down, producing negative force as the air inside the building pushes upward. If the wind gets strong enough, part or all of the roof can be ripped off because of this force. Similar negative forces are produced on walls that face sideways to the wind; windows are sometimes blown out by this pressure. Some negative pressure also occurs on the wall or walls facing away from the oncoming wind.

### PROBLEM 2-6

Suppose you look at an Internet site for tropical weather and learn that a hurricane has sustained winds of 120 kt. What is the equivalent wind speed in miles per hour? In kilometers per hour?

### SOLUTION 2-6

From the above discussion, we know that a wind speed of 1 kt is equal to approximately 1.151 mi/h. Therefore, 120 kt = 138 mi/h. A speed of 1 kt is equal to approximately 1.852 km/h. Therefore, 120 kt = 222 km/h.

## Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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