People can ________ running everywhere. Do you know what ________ ?

A. see; has happened

B. see; happens

C. be seen; is happened

D. be seen; is happening

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!

WHAT YOU’LL NEED: ● Soap           ● Water          ● Your hands! WHAT TO DO: 1. Make sure your hands are dry. 2. Rub your hands together until you feel the heat of your hands. 3. Now, use soap and water to get your hands very slippery (滑的). 4. Try to make friction happen while your hands are slippery. 5. Please write down what has happened. LET’S TALK! Friction is an energy that happens when two things rub together. When friction happens, it makes heat! When your hands are slippery, they won’t make very much friction and your hands won’t get so hot. DID YOU KNOW? 1. Friction happens when you stop your fast running bike. 2. Ancient people made fires by rubbing two pieces of wood together. Friction happened though they didn’t know it.         ?        Friction is everywhere. Have you ever noticed situations where friction is happening? If not, ask your parents to take you out in a car. If it is not too hot, touch the tires (轮胎) of the car before and after a short drive to see how much warmer they get from friction.

根据表格内容，选择正确答案。

1. 1.

   You’d better make your hands                 to get heat when you rub them

   1. A.
      slippery
   2. B.
      dry
   3. C.
      wet
   4. D.
      smooth
2. 2.

   What does the word “friction” in this text mean in Chinese?

   1. A.
      摩擦
   2. B.
      冷却
   3. C.
      膨胀
   4. D.
      震动
3. 3.

                           is NOT an example of friction

   1. A.
      Bike riding
   2. B.
      Car driving
   3. C.
      Hands rubbing
   4. D.
      Friction discovering
4. 4.

   What’s the last column (栏目)?

   1. A.
      THINK IT OVER!
   2. B.
      WHAT HAPPENED?
   3. C.
      EVERYDAY ACTION:
   4. D.
      WORK WITH PARENTS!
5. 5.

   This text is most probably                         

   1. A.
      a science report
   2. B.
      a car advertisement
   3. C.
      a rubbing introduction
   4. D.
      a chemistry programme