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(共24张PPT)
Unit 4 Natural disasters
Listening
What is an asteroid
Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids.
Part I Lead-in
There are millions of asteroids, many thought to be the shattered remnants of planetesimals（小行星体）, bodies within the young Sun’s solar nebula（太阳星云） that never grew large enough to become planets.
Only one asteroid, 4 Vesta（第4小行星）, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned.
As of June 2016, 14,464 near-Earth asteroids are known and the number over one kilometre in diameter is estimated to be 900–1,000.
Near-Earth asteroids, or NEAs, are asteroids that have orbits that pass close to that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth-crossers.
What will happen
What would you do
小行星的直径、撞击速度、撞击角度、撞击地点不同，撞击对地球造成的破坏力就不同。
不过，地球有很厚的大气保护，因此受到外来星体的碰撞是有概率的，受到直径越大的星体碰撞的概率越小。一般地，对地球而言，直径在10米左右的星体，每年约有10颗左右冲入地球大气层，约一两颗会落到地面，形成陨石或陨铁，不会造成什么严重的灾害。
小行星撞击地球
直径在50至100米左右的星体，
每100年约会有1颗冲入地球大气层，
有的掉到地面，所造成的灾害范围有限，落到哪儿哪儿倒霉；直径达1000米的星体，约10万年会有1颗冲入地球大气并撞击到地面上，会引起全球性的灾难（科学家猜测恐龙灭绝的原因之一）。
小行星撞击地球
因此，事实上最好的方法是，科学观测小行星，及时发现可能与地球相撞的星体，科学确定小行星的直径、速度、可能的撞击角度、撞击地点和撞击可能对地球造成的破坏力，再采取措施——比如发射深度撞击什么的，把该星体炸毁或者改变它的运行轨道，使之远离地球。
小行星撞击地球
Scared/frightened
An asteroid will travel very close to the earth and it may hit the earth.
Part II Pre-Listening
An asteroid is coming
asteroid n. 小行星
survival kit 救生包（装有食物、 医疗用品和工具）
New words and expressions
Listening
A Listen to two government announcements and a conversation. Then tick ( ) the thing each student is going to do when the asteroid hits the Earth.
An asteroid is coming
Part III While-Listening




B Listen to the recording again and decide whether the following sentences are T (True) or F (False).
Why does the government make the first announcement
What does the government advise people to do
What shall they put in their survival kit
Answer the following questions according to what you have listened.
Because an asteroid will travel very close to the Earth. It is possible that it will hit the Earth.
It advises people not to go outside.
Food, water and some medicine.
Role-play
In groups of five, role-play the conversation.
Part IV Post-Listening
Think and answer the following question.
Think and answer
What will you do if an asteroid hits the Earth
I will stay inside.
I will call my mum and dad
and say I love them.
…
Tapescripts
Radio announcer: This is a government
announcement. An asteroid will
travel very close to the Earth. It
is possible that it will hit the
Earth. Please do not go outside.
Arthur: What are we going to do, Helen
Helen: Oh, no! I’m only 14. I haven’t even started
my life! Barry, I’m scared.
Barry: Helen, don’t cry. I’m sure everything will be
OK.
Joseph: Well, I want to go home.
Arthur: No, Joseph. The government advised us
not to go outside. We should stay here.
Joseph: I’m going to phone my mum and dad. If
this is my last day on Earth, I want to say
“thank you” to my parents for everything
they’ve done for me. Arthur, is the phone
working
Arthur: Yes, it is. Go on and use it, Joseph. I’m
going to prepare a disaster survival kit.
What shall I put in my survival kit, Barry
Barry: Food, water and some medicine.
Helen: I’m going to make a list of everything I want
to do with my life if the asteroid doesn’t hit
the Earth.
Barry: That’s a good idea, Helen. I’m going to
think of all the good things in my life and
write them down.
Radio announcer: This is a government
announcement. The asteroid is
moving away from the Earth. It
will not hit the Earth!
Dictation
小行星
救生包（装有食物、医疗用品和工具）
asteroid
survival kit
Part V Review
Thank you!

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