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How Does Temperature Affect Air Movement?
Transcript of How Does Temperature Affect Air Movement?
Measuring Air Pressure
How Does Temperature Affect Air Movement?
Measuring Wind Direction and Speed
Your ears pop because of air pressure.
The earth is surrounded by a layer of air. Air is made of matter and has mass. Air presses down on the surface of the earth and on you too!
This pressing down of air is called air pressure. Usually you don't notice the pressure of the air, but you notice its effects.
For example, when you ride in an airplane, the change of air pressure pushes on your eardrum. When you swallow, your eardrum makes a popping noise.
As you go higher above the earth, the air pressure changed. The higher you fly, the less air there is. Less air is pressing down on you. Therefore, the air pressure is lower.
Air temperature changes as you go higher above the earth. Since the surface of the earth heats the air above it, the air is warmer near the ground.
Air pressure on the earth's surface also changes. Changes in temperature cause changes in air pressure. As the air near the surface of the earth becomes warmer, the particles becomes warmer, the the particles of the air move farther apart.
The air becomes lighter and rises.
The lighter air pushes down on the surface of the earth with less pressure. A low-pressure area forms.
Cold air is heavier than warm air. Its matter is more closely packed together. It pushes down harder on the earth's surface than warm air does. Therefore, a cold air mass is called a high-pressure area.
As you can see in the picture, air moves from a place with high pressure to a place with low pressure. The moving air is called wind. When the cooler air from a high-pressure area sinks toward the earth, it causes wind. Then you feel a nice, cool breeze. see C13
Air pressure can be measured using a barometer.
One type of barometer is made of a hollow tube that is closed at one end and opened at the other end. The tube is filled with mercury. Then the tube is turned upside down in a dish of mercury.
see C14 paragraph 1
The circular dial
The outside of the box moves slightly as air pressure changes. It is connected to a spring that moves a pointer on a dial. As the air pressure gets lower, the pointer moves to a lower number on the dial.
When the air pressure gets higher, the pointer moves to a higher number on the dial.
Even though it's invisible, you can tell wind's direction by watching objects move. Ex: a flag moving or the way a tree bends in the wind
You can wet your finger and hold it up to find the wind's direction. Your finger will feel cooler on the side the wind is blowing from.
For more exact measurements of the wind's direction, scientists use a wind vane. A wind vane rotates on top of a pole. It has a tail that can be pushed by the wind. The tail of the vane swings away from the wind. An arrow at the opposite end of the vane points into the wind. Some wind vanes have N,S,E, and W on them. It's one of the oldest tools for observing weather.
A wind sock shows wind direction. A wind sock also gives a good idea of how fast the wind is blowing.
If the sock stands straight out, the wind is blowing fast and strong. If the wind sock barely lifts in the breeze, the wind force is quite low. Airports often have wind socks set up, so that pilots can tell the direction and strength of the wind.
However, exact wind speed is measured using a tool called an anemometer. Anemometers are usually placed high above a roof or atop the mast of a boat.
An anemometer has 3 or 4 cups attached to the top of a pole. The cups are often shaped like half of a ping pong ball.
As the wind blows, it pushes the cups and causes this part of the anemometer to spin.
The number of spins per minute is changed to wind speed by gears, similar to the speedometer of an automobile.
When the wind blows fast, the anemometer spins very fast. Anemometers are often hooked up electrically to a dial that shows the wind speed.