Have you ever rubbed your hands together when they get cold? Why do we do that? We do that for friction. Friction happens when two things that aren't very smooth rub together to make heat energy. The faster you rub two things together, the more friction (and heat) you can make. Let's discover friction!

    The earth is about 4,600 million years old. Modern man has lived on the earth for only 35,000 years, but during that time, we have changed our planet in many ways. Many of the things that we have done are good, but more are not good for the earth.

    Water pollution

    A lot of people, birds and fish die each day because of water pollution. Factories have polluted the land and the water. As a result, many river and lakes are now dead.

    Air pollution

    In big cities, factories, as well as cars, trucks and buses are the biggest cause of air pollution. Many people in cities now have bad health problems. For example, Mexico city used to be a beautiful sunny capital, but today it is almost covered by thick brown clouds.

    Soil pollution

    In order to have a good harvest, most of the farmers use chemicals too much on their fields. That's bad for the soil. But this kind of pollution is difficult to stop.

    Hope for the future

    These problems are very serious for our future, so all of us should do something to improve our environment. If we can stop pollution, our planet will become more and more beautiful and our health will be better. Let's be greener people.

    In most parts of the world, many students help their schools make less pollution．They join environment clubs．In an environment club, people work together to make our environment clean．

    Here are some things students often do．

    No-garbage lunches．How many lunch bags do you throw away after lunch? Environment clubs ask students to bring their lunches in bags that can be used again．Every week they will choose the classes that make the least garbage and report them to the whole school．

    No-car day．On a no-car day, nobody comes to school in a car including the students and the teachers．Cars give pollution to us, so remember:

    Walk, jump, bike, or run!

    Use your legs! It's lots of fun!

    Turn off the water! Do you know that some toilets can waste twenty to forty cubic meters of water an hour? In a year, that would fill in a small river. In the environment clubs, students mend those broken toilets．

    We love our environment．Let's work together to make it better．

Find Which Direction Is South

    Do you have a good sense of direction? If not, please take with you a compass. But if you forget to take a compass, you can still find your way.

    It's never a good idea to imagine that the family member who was entrusted (委托) with the job of map-reading actually knows where the family is. You can tell by the slightly confused load on their faces that nothing on the ground seems to match the map. Never mind. The sun is shining and it's still morning.If you don't know the exact time, you can still find out where south is, but you'll need to be patient.

    ①Find a straight stick and put it in the ground in a place where you can mark its shadow.

    ②Try to position the stick as vertically(垂直)as you can. You can check this by making a simple plumb line (铅锤线) with a piece of string and weight. You haven't got any string? OK, use a thread from your clothes with a button tied at the end to act as a weight.

    ③Mark the end of the shadow cast by the stick.

    ④Wait approximately half an hour and mark the end of the shadow again.

    ⑤Keep doing this until you have made several marks.

    ⑥The mark nearest the stick will represent the shortest shadow, which is cast at midday, when the sun is highest in the sky and pointing to the exact south.

    ⑦Pick a point in the distance along the line between the shortest shadow and the stick.

    ⑧That point is south of where you are.

    ⑨Now you can turn the map, like you did before, and find which way you should be travelling.

Kids' health: Four steps for fighting stress

    Everybody gets stressed from time to time.{#blank#}1{#/blank#}Some ways of dealing with stress like screaming or hitting someone--don't solve (解决)much. But other ways like talking to someone you trust, can lead you to solve your problem or at least feel better.

    Try taking these four steps the next time you are stressed:

    ⑴Get support.   When you need help, reach out to the people who care about you. Talk to a trusted adult, such as a parent or other relatives.{#blank#}2{#/blank#}They might have had similar problems, such as dealing with a test, or the death of a beloved pet.

    ⑵Don't take it out on yourself.   Sometimes when kids are stressed and upset they take it out on themselves. Oh, dear, that's not a good idea. Remember that there are always people to help you. Don't take it out on yourself.{#blank#}3{#/blank#}

    ⑶Try to solve the problem.   After you're calm and you have support from adults and friends, it's time to get down to business.{#blank#}4{#/blank#}Even if you can't solve it all, you can solve a piece of it.

    ⑷Be positive.   Most stress is temporary (暂时的). Remember stress does go away, especially when you figure out the problem and start working on solving it. These steps aren't magic, but they do work~ And if you can stay positive as you make your way through a tough time, you'll help yourself feel better even faster.{#blank#}5{#/blank#}.

    Populations of white-tailed deer(白尾鹿) are growing rapidly in many parts of the United States. As populations grow, food becomes a problem. Many deer die of hunger. Others grow up small and unhealthy. In search of food, hungry deer move closer to where humans live. They eat farm crops, vegetables and even trees. Besides, increased numbers of deer near roads can cause traffic accidents.

    People admire the grace and fast speed of deer. Most people don't want these animals to be hungry and ill. Should people take action to control the growing deer populations?

Should People Take Direct Action?

    Many people think that hunting(打猎) is the best way to control the animal populations. Wildlife managers will see if there's enough food in an area and decide its carrying capacity(容量). Then hunters with licenses are sent to help control the number of deer. Hunting is usually not allowed in cities or suburbs, however.

    Some people have the idea to catch the deer and move them to other places. But this method is expensive and requires finding another place that can accept the deer without breaking the balance of ecosystem(生态系统).

    Scientists are also working to develop chemicals(化学药品) to control the birth rate(率) in deer populations. But this plan works for only one year at a time.

Should People Take Indirect Action?

    Some suggest bringing in natural enemies of deer, such as wolves, lions and bears, to areas with too many deer. But these animals could also hurt dogs, cats, and even humans. Other communities have built tall fences(篱笆) around areas to keep out the deer. However, this is impossible for farmers.

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    Some people are against any kind of action. They support leaving the deer alone. Animal populations in an area naturally go up and down over time. Doing nothing means that some deer will die of hunger or illness. But finally, the population will reach a size within the carrying capacity(容量) of the environment. So, let nature go its own way.