Originally aired during the week of October 13, 2008
We can't see it, we often forget it is completely surrounding us, and without it we couldn't survive. Here's a hint...you can feel it on a windy day. That's right, this week on The Montshire Minute we'll soar through the topic of air.
Air is a mixture of gases, primarily nitrogen (78%) and oxygen (21%) with a myriad of other components, such as argon, carbon dioxide, and neon.
The blanket of air surrounding Earth is called the atmosphere. It not only provides us with the air we breathe, but it protects us by absorbing ultraviolet solar radiation and reducing temperature extremes. The atmosphere is quite thin relative to the size of the Earth. If the Earth were the size of a basketball, a tightly held pillowcase would represent the thickness of the atmosphere.
Homeschoolers can further explore the topic of air at the Montshire starting on October 20 with a three-part series, All About Air.
Though we tend to use terms like "lighter than air," air molecules actually have weight and take up space. The weight of air, which is pulled down by gravity, comprises a force called air pressure. We don't usually notice, however, because our bodies exert a counterbalancing pressure.
You can see the effects of air pressure by doing a simple experiment at home. Fill a glass to the brim with water. Place a square of cardboard on top of the glass, making sure it covers the entire opening. Now, while holding the cardboard in place with one hand, carefully turn the glass upside down. (By the way, make sure to do this experiment over the sink.) Carefully release the cardboard, and voila, it stays in place! Why? Air is pressing up on the cardboard with enough force to hold the water in the glass.
Homeschoolers can further experiment with air at the Montshire starting on October 20 through a three-part series, All About Air.
There is no distinct boundary between Earth's atmosphere and outer space. The atmosphere (or air) just fades away with increasing altitude. Air molecules are packed most tightly together near the bottom of the atmosphere. In fact, 99% of all air is located within 31 miles of the Earth's surface, in the troposphere and stratosphere layers.
Since air is most dense at the Earth's surface, as we go up (in an airplane, hot air balloon, or even hiking a mountain), air pressure decreases. It makes sense really, as there is less air above weighing down on us. Changes in air pressure, especially rather quick changes, can affect your body. Think of the popping or pain in your ears when you take off in an airplane or drive down from your favorite ski resort.
Homeschoolers can further explore the topic of air at the Montshire starting on October 20 with a three-part series, All About Air. Visit www.montshire.org for more details.
Air pressure varies over time and can be measured with an instrument called a barometer. (Indeed, another name for air pressure is barometric pressure.)
Changes in air pressure bring about changes in weather. For example, the movement of air from a region of high pressure to a region of low pressure causes wind. Remember this with the saying: "Winds blow from high to low."
Think of that this winter when you feel a cold draft at home. Cold air enters the room, say under a door, and as it is warmed by the radiator, it lightens and rises to the ceiling, making room for more cold air to come in underneath. This phenomenon is called a convection current. You may just call it "drafty!"
Homeschoolers can further explore air at the Montshire starting on October 20 with the series All About Air. For more details visit www.Montshire.org.
Mark Twain once remarked that he counted 136 different kinds of weather in New England within a twenty-four hour period. Imagine now that during those same 24 hours, you had been flying circles in a jet plane over the same area. Would you have observed the tumult described by Twain? No, your experience would have been much calmer, as almost all of the events that we call weather occur within about 5 miles of the Earth's surface.
Back on the ground, one of the reasons for New England's quickly changing weather relates to the shape of the landscape. Mountains can dramatically affect temperature. For example, air forced up mountainsides cools about 3 1/2 degrees Fahrenheit for every 1,000-foot rise. Mount Washington, at over 6,000 feet above sea level, is often about 20 degrees cooler than it is at the Montshire Museum, which is about 450 feet above sea level.
