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．
(1)
You’d better make your hands _______ to get heat when you rub them．
[ ]
A．
slippery
B．
dry
C．
wet
D．
smooth
(2)
What does the word “friction” in this text mean in Chinese?
How much sleep do we need? The answers are different. Some people need only three hours of sleep a night. Others need ten hours of sleep a night. Most Amexicans sleep for an average of seven to eight hours a night. After age fifty, the average sleep hours go down to 6.5 hours a night.
Most people will have a bad night when they can't fall asleep. About one in three Americans has a problem with sleep. Many of these people cannot fall asleep. The name of this problem is called insomnia(失眠症).
This is not a new problem. Many famous people in history had insomnia .Some of these people had their own ways to sleep well. Benjamin Franklin(本杰明·富兰克林), the famous inventor, had four beds.He moved from one to another to fall asleep. King Louis XIV (国王路易十四) of France had 413 beds and hoped to fall asleep in one of them. Mark Twain, the famous writer, had a different way: he hy on his side(侧卧) across the end of the bed!
(1)
Most Americans usually sleep for about _________ hours a night.
A. 3 B. 5～6 C. 10 D. 7～8
[ ]
(2)
As people grow older,they need __________ at night.
A. less sleeping time
B. more sleeping time
C. the same amount of sleeping time
D. a fixed time to sleep
[ ]
(3)
If there are 100 million people in the US hav-ing a problem with sleep,what's the popula-tion of it? About _______.
A. 200 million B. 300 million C. 600 million D. 900 million
[ ]
(4)
Franklin tried to go to sleep by __________.
A. moving from one to another of his 413 beds B. moving from one to another of his 4 beds
C. inventing a bed for himself D. lying on his side across the end of the bed
[ ]
(5)
It's not mentioned in the passage,but we know that Mark Twain was ___________.
