Transcript 能量 - web

Energy (能量)
What is Energy
• Energy Is the Ability to Do Work.(完成工作
的能力)
• Energy causes things to happen around
us.
• When a car drives by, it is being powered
by gasoline, a type of stored energy.
• The food we eat contains energy. We use
that energy to work and play.
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• Energy can be found in a number of
different forms. It can be chemical energy
(化學能), electrical energy (電能), heat
(thermal energy)(熱能), light (radiant
energy)(光能), mechanical energy(機械能),
and nuclear energy (核能).
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• Energy makes everything happen and can
be divided into two types:
• Stored energy is called potential energy
(潛能).
• Moving energy is called kinetic energy (動
能).
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How Do We Measure Energy?
• One of the basic measuring blocks is
called a Btu. This stands for British thermal
unit (英國熱量單位) and was invented by,
of course, the English.
• Btu is the amount of heat energy it takes
to raise the temperature of one pound of
water by one degree Fahrenheit, at sea
level. (將一英磅重的水溫增加一度所需的熱
量就是一個Btu)
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• One Btu equals about one blue-tip kitchen
match. (一個Btu等於一根火柴燃燒的熱量)
• One thousand Btus roughly equals: One
average candy bar or 4/5 of a peanut
butter and jelly sandwich.
• It takes about 2,000 Btus to make a pot of
coffee. (加熱一壺咖啡需2,000 Btus)
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• Energy also can be measured in joules (焦
耳). Joules sounds exactly like the word
jewels, as in diamonds and emeralds (綠
寶石). A thousand joules is equal to a
British thermal unit.
• 1,000 joules = 1 Btu
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• The term "joule" is named after an English
scientist James Prescott Joule who lived
from 1818 to 1889. He discovered that
heat is a type of energy. (焦耳先生發現熱
就是一種能量)
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• One joule is the amount of energy needed
to lift something weighing one pound to a
height of nine inches. So, if you lifted a
five-pound sack of sugar from the floor to
the top of a counter (27 inches), you would
use about 15 joules of energy. (一焦耳的
能量等於將一英磅重的物品提高九英吋高
度所需的熱量)
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• Around the world, scientists measure
energy in joules rather than Btus. It's much
like people around the world using the
metric system (公制) of meters and
kilograms, instead of the English system of
feet and pounds.
• Like in the metric system, you can have
kilojoules -- "kilo" means 1,000.
1,000 joules = 1 kilojoule = 1 Btu
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• A piece of buttered toast contains about
315 kilojoules (315,000 joules) of energy.
With that energy you could:
• Jog (慢跑) for 6 minutes
• Bicycle for 10 minutes
• Walk briskly (迅速地) for 15 minutes
• Sleep for 1-1/2 hours
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• Run a car for 7 seconds at 80 kilometers
per hour (about 50 miles per hour)
• Light a 60-watt light bulb for 1-1/2 hours
• Or lift that sack of sugar from the floor to
the counter 21,000 times!
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Changing Energy
• Energy can be transformed into another
sort of energy. But it cannot be created
AND it cannot be destroyed (能量不滅定
律). Energy has always existed in one
form or another. (能量的形式會改變但是總
量不變)
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• Stored energy in a flashlight's (手電筒)
batteries becomes light energy when the
flashlight is turned on. 10123804
• Food is stored energy. It is stored as a
chemical with potential energy. When your
body uses that stored energy to do work, it
becomes kinetic energy. (以飲食為例)
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• If you overeat, the energy in food is not
"burned" but is stored as potential energy
in fat cells. (當飲食過量，多餘的能量儲存
於脂肪細胞作為潛能)
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• When you talk on the phone, your voice is
transformed into electrical energy, which
passes over wires (or is transmitted
through the air). The phone on the other
end changes the electrical energy into
sound energy through the speaker. (以打
電話為例)
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• A car uses stored chemical energy in
gasoline to move. The engine changes the
chemical energy into heat and kinetic
energy to power the car. (以汽車為例)
• A toaster changes electrical energy into
heat and light energy. (If you look into the
toaster, you'll see the glowing wires.) (烤麵
包機)
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Food Energy
• Energy changes form at each step in the
food chain. Take an ear of corn as an
example.
• Sunlight is taken in by the leaves on the
corn stalk and transformed through
photosynthesis (光合作用).
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• The plant takes in sunlight and combines it with
carbon dioxide (二氧化碳) from the air and water
and minerals (礦物質) from the ground.
• The plant grows tall and creates the ears of corn
- its seeds (種子). The energy of the sunlight is
stored in the leaves and inside the corn kernels
(顆粒). The corn kernels are full of energy stored
as sugars and starch (澱粉).
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• The corn is harvested and is fed to
chickens and other animals. The chickens
use the stored energy in the corn on the
cob (玉米穗軸) to grow and to move.
Some energy is stored in the animal in its
muscle tissue (肌肉組織) (protein，蛋白質)
and in the fat (脂肪).
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• You then eat the chicken's meat and fat
and convert that stored energy into energy
in your own body.
• As your body uses the energy from the
chicken, you breathe (吸) in oxygen and
exhale (呼) carbon dioxide. That carbon
dioxide is then used by other plants to
grow.
• So, it's a big circle! #10183804
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Heat Energy
• Heat is a form of energy. We use it for a
lot of things, like warming our homes and
cooking our food.
Heat energy moves in three ways:
• Conduction (傳導)
• Convection (對流)
• Radiation (幅射)
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Conduction (傳導)
• Conduction occurs when energy is passed
directly from one item to another. If you
stirred a pan of soup on the stove with a
metal spoon, the spoon will heat up. The
heat is being conducted from the hot area
of the soup to the colder area of spoon.
(能量直接由一個物體傳至另一個物體就是
傳導)
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Convection (對流)
• Convection is the movement of gases (氣
體) or liquids (液體) from a cooler spot to a
warmer spot. If a soup pan is made of
glass, we could see the movement of
convection currents in the pan. The
warmer soup moves up from the heated
area at the bottom of the pan to the top
where it is cooler.
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• The cooler soup then moves to take the
warmer soup's place. The movement is in
a circular pattern within the pan. (氣體或液
體由低溫處移至高溫處就是對流)
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• The wind we feel outside is often the result
of convection currents. You can
understand this by the winds you feel near
an ocean. Warm air is lighter than cold air
and so it rises. During the daytime, cool air
over water moves to replace the air rising
up as the land warms the air over it.
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• During the nighttime, the directions
change -- the surface of the water is
sometimes warmer and the land is cooler.
(以風的移動為例，由於暖空氣上升，日間
風由海吹向陸地 (較暖)，晚間則因海水含
熱量而相反)
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Radiation (幅射)
• Radiation is the final form of movement of
heat energy. The sun‘s light and heat
cannot reach us by conduction or
convection because space is almost
completely empty. There is nothing to
transfer the energy from the sun to the
earth. (幅射是能量不藉媒介物的傳送)
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• The sun's rays travel in straight lines
called heat rays. When it moves that way,
it is called radiation.
• When sunlight hits the earth, its radiation
is absorbed (吸收) or reflected (反射).
Darker surfaces absorb more of the
radiation and lighter surfaces reflect the
radiation. So you would be cooler if you
wear light or white clothes in the summer.
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Energy Star
• The EPA Energy Star label (能量之星) first
began appearing on a few computer
monitors back in 1992. Today the Energy
Star -- a certification of money-saving
energy efficiency and earth-saving
environmental "greenness"
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nuclear energy
• Matter (質量) can be changed into energy.
The world's most famous scientist, Albert
Einstein, created the mathematical formula
that explains this. It is:
• E = m c2
• This equation says:
E [energy] equals m [mass] times c2
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• [c stands for the velocity or the speed of
light (光速). c2 means c times c, or the
speed of light raised to the second power - or c-squared.]
• This equation is the key to unlock atomic
energy (原子能) and also create atomic
bombs (原子彈).
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• The ancient Greeks said the smallest part of
nature is an atom. But they did not know 2,000
years ago about nature's even smaller parts.
• Atoms are made up of smaller particles -- a
nucleus (原子核) of protons (質子) and neutrons
(中子), surrounded by electrons (電子) which
swirl (旋轉) around the nucleus much like the
earth revolves (公轉) around the sun.
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Nuclear Fission (分裂)
• An atom's nucleus can be split apart.
When this is done, a tremendous amount
of energy is released. The energy is both
heat and light energy. Einstein said that a
very small amount of matter contains a
very LARGE amount of energy.
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• This energy, when let out slowly, can be
harnessed (利用) to generate electricity.
When it is let out all at once, it can make a
tremendous explosion in an atomic
bomb.1026/3804
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• The word fission means to split apart.
Inside the reactor of an atomic power plant,
uranium (鈾) atoms are split apart in a
controlled chain reaction.
• In a chain reaction, particles released by
the splitting of the atom go off and strike
other uranium atoms splitting those.
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• Those particles given off split still other
atoms in a chain reaction. In nuclear
power plants (核電廠), control rods are
used to keep the splitting regulated so it
doesn't go too fast.
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• If the reaction is not controlled, you could
have an atomic bomb. But in atomic
bombs, almost pure pieces of the element
Uranium-235 or Plutonium (鈽，94Pu239),
of a precise mass and shape, must be
brought together and held together, with
great force. These conditions are not
present in a nuclear reactor (反應爐).
10253902
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Nuclear Fusion (融合)
• Another form of nuclear energy is called
fusion. Fusion means joining smaller
nuclei (the plural of nucleus) to make a
larger nucleus. The sun uses nuclear
fusion of hydrogen (氫) atoms into helium
(氦) atoms. This gives off heat and light
and other radiation.
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• Two types of hydrogen atoms, deuterium (氘,重
氫) and tritium (氚,超重氫), combine to make a
helium atom and an extra particle called a
neutron.
Thanks to the University of California, Berkeley for the picture.
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