What is a computer virus?

A virus is a malicious software program that infects computer files or hard disk drives and then makes copies of itself. Many activities that kids do online can leave computers vulnerable to viruses. E-mail attachments are a common means of distributing viruses, but viruses can also be downloaded when you share files and open instant message attachments. In order to keep your computer safe, never open an e-mail attachment you haven’t requested.

Send an e-mail to friends to confirm that they meant to send you an attachment. Also, you can configure your instant messaging program so you can’t receive files from other users. Never download any program without checking with a parent first. You can protect your computer by always running up-to-date firewall software, by running antivirus software regularly, and by periodically scanning your computer for spyware or other unwanted software and immediately removing it.

Why do dogs bark?

Dogs bark to communicate with other dogs and with humans. Dogs are descendants of wolves, which are social animals that live in packs, and they share many of the behaviors that define the complex relationships that exist within such animal groups. Few domestic dogs live together in packs (though they often consider their human family their group), but they still use complicated behaviors that involve smell, sight, and hearing to communicate. A dog has many scent-producing glands that it uses to communicate. The scent that a dog leaves behind (in its urine, feces, and paw prints) can reveal its sex, age, and even its mood to other dogs that come sniffing by.

A dog uses its posture, facial expression, and ear and tail position to communicate with other dogs, too. And it uses its voice to communicate by whining, growling, howling, or barking. A dog usually whines or whimpers when it is in distress: when it is hungry, cold, or in pain. Growls indicate that a dog is angry and ready to fight. Barks usually show excitement.

Why is Jell-O® so wobbly?

Jell-O® is made from gelatin, a processed protein that makes it wobbly. Gelatin is made from the collagen in cow or pig bones and skins. Gelatin melts when heated and solidifies when cooled again. When you add the Jell-O® powder to boiling water, the powder dissolves and the weak bonds that hold together the protein chains start breaking apart.

The chains float around in the mixing bowl until you add cold water. As the Jell-O® cools, the chains start bonding again. The chains become tangled when they are stirred, and water gets into gaps between the chains. Once it is refrigerated, the gelatin “chains” harden and the trapped water and flavor make Jell-O® wobbly.

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Why are polar bears white?

The polar bear lives in the Arctic, the region of the North Pole. Most of its environment is barren, covered year-round with ice and snow and not much else. A polar bear might eat what few plants it can find, but it feeds mostly on water animals like seals and small walruses, which share its frozen home. The polar bear’s yellowishwhite coat helps it blend into its snowy surroundings as it hunts its prey.

After all, there is not much in the Arctic to hide behind! The fur of a polar bear is also extremely thick, allowing it to withstand polar temperatures and swim in Arctic waters, where its prey is often found. Polar bears are excellent swimmers, and their unique paws—with hairy soles—allow them to run very quickly over ice and snow without slipping.

Why when suggesting an exhaustive search do we say,“Leave no stone unturned”?

The advice to “leave no stone unturned” comes from Greek mythology, Wherein the Oracle of Delphi, through his communication with the gods, had acquired great wisdom.

Euripides wrote that When the oracle was consulted about how to find a defeated general’s hidden treasure, he advised that the only way was “to leave no stone unturned.” The expression and the advice have been with us ever since.

What does my brain do, besides think?

The brain is the body’s command center; everything we do—eating, talking, walking, thinking, remembering, sleeping—is controlled and processed by the brain. As the most complex organ in the human body, the brain tells us what’s going on outside our bodies (whether we are cold or hot, for instance, or whether the person we see coming toward us is a friend or a stranger) as well as what’s going on inside our bodies (whether we have an infection or a broken bone, or whether we feel happy or sad).

The key to the body’s nervous system, the brain contains between 10 billion and 100 billion nerve cells, or neurons. Neurons combine to form the body’s nerves, thin cords that spread from head to toe and all parts in between. Neurons take in and send out electrical signals, called impulses, that control or respond to everything your body does and feels. The brain is like a very busy, high-speed post office, constantly receiving messages and sending them out all the time; it handles millions of nerve impulses every second.

Why are barns usually painted red?

Paint coats wood, protecting it from sunlight and rain damage and making it last longer. When early farmers had enough money to paint their barns, they usually used inexpensive paint because the structures were so large. Ferrous oxide, a chemical powder that gives paint its red color, was readily available and cost little. Thrifty farmers in New England, New York, and the upper Midwest region painted their barns red. In those places, red barns remain a tradition. But there are plenty of barns in other parts of the country that are not red. Early farmers that were poor—especially in regions like Appalachia and the South—left their barns unpainted because they did not have the money to do the job.

Unpainted wood usually weathers to a soft gray color. And in places like Pennsylvania, Maryland, and some southern Midwestern states, the most frequently seen barn color is white. Some people think that white barns grew popular when dairy farming became more important after the Civil War; white suggests cleanliness and purity, desirable qualities to be associated with milk production. Special farms where fancy horses or prize livestock were raised sometimes had barns painted unusual colors, like yellow, green, or black.

Why do some people have freckles?

People with light skin and eyes are more likely to have freckles because they have less melanin, a chemical in the skin that protects it from sun damage by reflecting and absorbing ultraviolet (UV) rays. Instead of tanning, they freckle.

Some people’s freckles fade away almost completely in the winter, and then return in the summer, when the person is more likely to sunburn. Sunscreen can help protect everyone (freckled or not) from the Sun’s harmful rays.

What exactly is a “family circle”?

When the early Normans brought fire indoors they built semicircular open fireplaces. To keep warm at night or when the air was cool, the family would sit in a semicircle opposite the one formed by the hearth, creating a complete circle where they would spend time telling stories or singing songs within what they called the “family circle.” When neighbours were included, it became “a circle of friends.”

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