Monthly Archives: October, 2009
How does a smoke deterctor work?
Every modern business building nowadays is equipped with smoke detectors (also known as smoke alarms) that have the potential to save millions of lives at very little cost. The little contraption consists of two basic parts: a sensor (to detect smoke) and an electronic audible alarm (to rouse people up). We’ll look into how an …
How can you make oil sink in water?
An object will float or sink in a liquid, depending on its density. Density is a property of matter that tells us how heavy something is for its size. For oil and water, liquids deemed to be immiscible. But still, oil can sink in water. How? There are several ways. One, you can opt for …
What is the difference between a hill and a mountain?
A hill or a mountain is a part of the land that is higher than the land around it. While a mountain is generally thought of as being much larger than a hill, there is actually no clear-cut difference between them. The word “mountain” means different things to different people. Wheat is called a mountain …
How does a sundial tell time?
Long before we had clocks and watches, people used sundial to tell time. A sundial is really a shadow clock – it tells the time by the sun’s shadow. A sundial consists of the dial face and the gnomon (pointer), which is set in the center of the dial. The dial is divided into hours. …
Why does a fire smoke?
We’ve all see smoke rising from a bonfire or the chimneys of factories and houses. When a log in a fireplace burns, some of the burning wood is changed into invisible gases. These hot gases, which consist mostly of water vapor and carbon dioxide. Are very light. They rise up the chimney and drift away …
What makes an ECHO?
If you shout or clap your hands in a canyon, the sound may make an echo. An echo is a sound that we hear after it is reflected, or bounced back, from some large obstacle. When you call out in a canyon, the sound waves of your voice travel through the air in all directions. …
How is rope made?
If you inspect a piece of rope, you’ll see it is made by many tough, threadlike fibers twisted together. The best rope fibers came from the long leaf stems and stalk of a plant called the abaca plant, which grows in the Philippines. This fiber is generally known as Manila hemps. Almost all rope is …
What is a greenhouse?
A greenhouse is a glass building to which flowers and other plants can be grown all year – even when the ground is white with snow. No matter what the weather is like outside, it’s always just right for the plants inside a greenhouse. The glass roof and walls let in just the right amount …
Where does wax come from?
When we think of wax, we may think of the soft, solid material that candles are made of. There are many kinds of wax and many uses for them. Wax comes from animal, vegetable, and mineral sources. The wax used for making most candles and for sealing jars of homemade jelly is called paraffin. Paraffin …
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