WHY DOES FROST FORM ON WINDOWS?

Children who live in places where the winter get cold love to see frost on the windows. some of the patterns are quite beautiful and look like intricate designs on trees or leaves.

For this frost to form on the windowpanes-as well as on trees and grass-certain condition are necessary. Frost is made up of tiny crystals of frozen water. It forms when air that has a lot of moisture in it is cooled below the freezing temperature of water. This temperature, which we call "the freezing point," is 32 degrees Fahrenheit and zero degree centigrade, at sea level.

When air becomes cooler, it cannot hold as much water as before. The excess water condenses on such object as the windowpane. Now, if the temperature falls below 32 degrees Fahrenheit, this water becomes crystallized. in other words, it freezes into a coating of interlocked crystals of water.

What causes the patterns to appear in the frost on the windowpanes? For one thing, the tiny crystals have a certain structure which gives them a pattern. In addition, there may be create the designs that "jack Frost" makes on your windows.

White frost, which is often called "hoarfrost," is of two kinds: granular and crystalline. Granular frost is simply frozen fog. The crystalline frost, which we have described, is formed directly from the water vapor in the air. It goes right from being a gas to being a solid, without going through the liquid state.

Frost , as you know, can be a serious danger for the farmer by killing buds or ripening fruit. Actually, it is not the  frost itself, but the freezing of the plant juices that it is harmful. So farmers have had to develop ways of preventing frost to save their crops. One way is to cover the plants with a light cloth to prevent radiation of heat. Smudge pots in orchards cover the tree with thick smoke, and this also helps the plants hold in their heat.

So while you enjoy seeing the work of "jack Frost," remember that it may serious damage to millions of pounds worth of crops.

WHY DO SNOWFLAKES HAVE SIX SIDES?

One of the most beautiful objects formed by nature is a snowflake. It would take most of us a long time to “design” a shape as beautiful as a single snowflake. Yet in an ordinary snowstorm, billions upon billions of snowflakes fall to the earth-and no two are exactly alike!

Snow, as you may know, is just frozen water. In fact, you may ask why snow is white if it’s just frozen water. Shouldn’t it be colorless? The white appearance is caused by the fact that the many surfaces in all the ice crystals that make up a snowflake reflect light, and we therefore see it as white.

When water freezes, it forms crystals. This simply means that the molecules come together in a special arrangement, or geometrical form, and we call this “a Crystal.”

It so happens that a water molecule consists of three units-two atoms of hydrogen and one of oxygen. So when it crystallizes, it has to form either three-sided or sis-sided figures.

The water that freezes to form snow is in the form of water vapor in the atmosphere. As it freezes, the crystals that form are so small that they are invisible, but when snow is being formed, these crystals are carried up and down in the atmosphere by air currents.

As they move up and down, a group of crystals begin to collect around something. It might be around a speck of dust, or around a tiny drop of water. The group of crystals gets larger and larger, so that soon there might be hundreds of crystals gathered around one nucleus.

When such a group becomes large enough, it begins to float down toward the ground and we call it “a snowflake.” Some snowflakes are more than an inch in diameter! The size of a snowflake depends on the temperature. The colder the temperature, the smaller the snowflakes that will form.

Did you know that in many parts of the world snow has fallen that has been blue, green, red, and even black? This is due to the presence of certain fungi or dust in the air around which the snowflakes formed.

WHAT IS DEW?

You would imagine that dew is a very simple phenomenon of nature, easily understood and explained. Yet strangely enough, exactly what dew is have long been misunderstood, and whole books have been written on the subject!

Since the days of Aristotle until about 200 years ago, it was believed that dew “fell,” somewhat like rain. But dew doesn’t fall at all! The most familiar form of dew, seen on the leaves of plants, is now known not to be all dew! So you see, there have been many wrong ideas about dew.

In order to understand what dew is, we have to understand something about the air around us. All air holds a certain amount of moisture. Warm air can hold much more water vapor than cold air. When the air comes in contact with a cool surface, some of that air becomes condensed and thee moisture in it is deposited on the surface in tiny drops. This is dew.

The temperature of the cool surface, however, has to drop below a certain point before dew will form. That point is called “the dew point.” For example, if you place water in a grass or a polished metal container, dew may not collect on the surface. If you place some ice in the water, dew may still not collect until the surface of the glass or container is brought down to a certain point.

How does dew form in nature? First, there has to be moisture-laden warm air. This air must come into contact with a cool surface. Dew doesn’t form on the ground or sidewalk, because it still remains warm after having been heated by the sun. But it may form on grasses or plants which have become cool.

Then why did we say that the dew seen on plants is really not dew? The reason is that while a small part of the moisture seen on plants in the morning is dew, most of it-and in some cases all of it- has really come from the plant itself! The moisture comes out through the pores of the leaves. It is a continuation of the plant’s irrigation process for supplying the leaves with water from the soil. The action starts in the daytime, so that the surface of the leaf should be able to withstand the hot sun, and it simply continues into the night.

In some places in the world, enough dew is deposited every night for it to be collected in dew ponds and used as a water supply for cattle!

HOW FAST DOES SOUND TRAVEL?

Every time a sound is made, there is some vibrating object somewhere. Something is moving back and forth rapidly. Sound starts with a vibrating object.

But sound must travel in something. It requires something to carry the sound from its source to the hearer. This is called “a medium.” A medium can be practically anything-air, water, objects, even the earth. The Indians used to put their ears to the ground to hear a distant noise!

No medium-no sound. If you create a vacuum, space containing no air or any other substance, sound cannot travel through it. The reason for this is that sound travels in waves. The vibrating objects cause the molecules or particles in the substance next to them to vibrate. Each particle passes on the motion to the particle next to it, and the result is sound waves.

Since the mediums in which sound travels can range from wood to air to water, obviously the sound waves will travel at different speeds. So when we ask how fast does sound travel, we have to ask: In what?

The speed of sound in air is about 1,100 feet per second (750 miles per hour). But this is when the temperature is 32 degrees Fahrenheit. As the temperature rises, the speed of sound rises.

Sound travels much faster in water than in air. When water is at a temperature of 46 degrees Fahrenheit, sound travels through it at about 4,708 feet per second, or 3,210 miles per hour. And in steel, sound travels at about 11,160 miles per hour!

You might imagine that a loud sound would travel faster than a weak sound, but this isn’t so. Nor is the speed of sound affected its pitch (high or low). The speed depends on the medium through which it is traveling.

If you want to try an interesting experiment with sound, clap two stones together when you are standing in the water. Now go under water and clap those two stones together again. You’ll be amazed how much better sound travels through water than through air!