Transcript Energy - Images

Chapters 3 & 4
Objectives
• Recognize how energy causes change.
• Describe common forms of energy.
• Illustrate that the two general types of
energy are kinetic energy and potential
energy.
Different Forms of Energy Have
Different Uses
• Energy takes on many forms.
• Lamps use electrical energy while plants
use energy from the sun to grow.
Energy: ability to cause change (4)
• All forms of energy have one important
point in common--- they cause change to
occur.
• The flow of electrical energy through a
wire causes a cool, dark bulb to get hot
and glow.
• You are a source of energy that makes
changes in your environment!
What in this picture is using energy?
Forms of Energy (6)
•
•
•
•
•
•
Mechanical Energy
Sound Energy
Chemical Energy
Thermal Energy
Electromagnetic Energy
Nuclear Energy
Mechanical Energy
• Energy that moves
objects is mechanical
energy.
• The energy that you
use to put book on a
shelf is mechanical
energy, s is energy
that a person uses to
turn car key.
Sound Energy
• Vibrations of particles
• When you hear a car
drive by, you are
detecting vibrations in
the air produced by
sound energy.
• Cannot travel through
empty space.
Chemical Energy
• Energy that is stored in chemical
compositions of matter.
• Example: When wood or gasoline burns,
chemical energy produces heat.
• The energy used by your body cells
comes from chemicl energy.
Thermal Energy
• The total amount of
energy from the
movement of particles
in matter is thermal
energy.
• The energy of this
motion in an object is
the object’s thermal
energy.
Electromagnetic Energy (13)
• Transmitted through space in the form of
electromagnetic waves.
• Include visible light, x-rays, and
microwaves.
• The sun releases a large amount of
electromagnetic energy, some of which is
absorbed by Earth.
Nuclear Energy (14)
• The center of an
atom– it’s nucleus– is
the source of nuclear
energy.
• When a heavy atom’s
nucleus breaks apart
or when the nuclei of
two small atoms join
together, energy is
released.
Nuclear Energy
• Everything has a beginning, and nuclear energy is no
exception. The first reactor to use nuclear energy was
built in 1942. The discovery of fission, that lead to
nuclear energy, was discovered a few years earlier. A
man named Enrico Fermi first discovered fission. In
1934, Fermi proved that neutrons could split atoms. This
was breaking news. The particles made by these splits
were lighter than the original atom. Later the scientist
added up the particles, and still it weighed less than the
original product. This proved that Einstein's theory was
right, that some of the mass changed to energy. This
theory was none other than e=mc2. The uses of this
energy would be great. From cities, to ships, to bombs,
nuclear energy powers them all.
Kinetic Energy
• The energy of motion is called Kinetic
energy. (16)
• Kinetic energy increases as mass
increases. (17-18)
– For example is a bowling ball and a soccor
ball were moving at the same speed, the
bowling ball would have more kinetic energy
because of its greater mass.
Kinetic Energy
• Kinetic energy increases as speed
increases.
– If two identical bowling balls were rolling along
at different speeds, the faster one would have
more kinetic energy because of its greater
speed.
Potential Energy
• Potential Energy is the
stored energy that an
object has due to its
position or chemical
composition. (19)
• P. 75-76
• EX) energy stored in
food (chemical energy)
is also potential
energy (22)
Review
• Give three ways you use energy. How
does each example involve a change?
• What two factors determine an object’s
kinetic energy?
3.2 & 3.3 Objectives
• You will learn
– How energy can be converted from one form
to another
– About the law of conservation of energy
– How energy conversions may be inefficient
– How technology can improve energy
conversions
Energy can change forms but is
NEVER Lost!
• Potential energy is stored in the chemicals
on the head of a match. The flame of a
burning match releases that energy as
light and heat. Where does the energy to
strike the match come from in the first
place.
Energy Changes Forms
• Matches chemical energy stored can be
changed to light and heat.
• Photosynthesis
• Page 78
Conversions between Potential
Energy and Kinetic Energy
• Potential energy can be changed into
kinetic energy and back into potential
energy.
• Page 79
Using Energy Conversions
• Page 80-81
Energy is Always Conserved
• As the soccer ball rolls, it rubs against
the ground. Some kinetic energy
changes into heat because of friction.
(30)
• Some of the ball’s energy changes to
sound energy as you hear the ball roll.
• Although the ball loses kinetic energy, the
overall amount of energy in the universe
does not decrease.
Energy is Always Conserved
• In the soccer ball, the ball loses energy,
but this energy is transferred to other parts
of the universe. Energy is conserved.
• The Law of Conservation of Energystates that energy can neither be
created nor destroyed. (29)
• Balance of Energy
Energy Conversions may produce
unwanted forms of energy
• When energy
changes forms, the
total amount of
energy is conserved.
• However, the amount
of useful energy is
almost always less
than the total amount
of energy.
Energy Efficiency
• Energy Efficiency is a
measurement of usable
energy after an energy
conversion. (32)
• Example: Energy-efficient
house-hold appliances.
These appliances convert a
greater percentage of
energy into the desired
form than inefficient forms.
Solar Cells
• Made of several layers of light sensitive
materials that convert sunlight directly
into electrical energy (36)
Review
• Describe an energy conversion you have
observed in your own life.
• What is the Law of Conservation of
Energy?
• Give an example of an energy conversion
that produces unwanted forms of energy.
Chapter 4
Temperature and Heat
All Matter is Made of Moving
Particles
• All matters is made up of atoms, and
atoms are always in motion, even if the
objects themselves do not change their
position.
• The motion of these tiny particles gives the
object energy.
The Kinetic Theory of Matter
•
The Kinetic Theory of Matter states that
all of the particles that make up matter
are constantly in motion.
1. Solid: Particles in solids are held tightly
together but are always in motion.
2. Liquid: Particles in liquids slide by one
another and are always in motion.
3. Gas: Particles in gases are completely
free to move and are always in motion.
Temperature and Kinetic Energy
• Particles move at different speeds have
different kinetic energies
• Temperature is a measure of the
average kinetic energy of all the
particles in an object. (45)
Particles Move Fast
Particles Move Slow
Temperature and Kinetic Energy
• We experience the connection between
temp. and energy everyday.
• For example: On a cold day, you warm
your hands by putting them near a fire.
The added energy makes the particles in
your hand move faster.
Temperature Measured
• In two common scales, temperature is
measured in units called, degrees (°)
• Farenheit: 32°- Freezing; 212°- Boiling
• Celsius: 0°C- Freezing; 100°C- Boiling
• A thermometer is used to measure
temperature (48)
Liquid Thermometers
• Liquid-filled thermometers measure
how much the liquid expands in a
narrow tube as the temperature
increases.
• Mercury is dangerous to handle so
many thermometers today are filled
with alcohol instead.
• Alcohol expands evenly as
temperatures increase & contracts
evenly when temperatures decrease
(add)
Thermal Expansion
• The property that makes liquidfilled thermometers work is
called thermal expansion.
• Example: Construction
engineers often have to take
thermal expansion into
account because steel and
concrete both expand with
increasing temperature. (49)
• The Gateway Arch p. 108
Why does water warm up so slowly?
• As Compared with
Butter and Oil?
Because more energy
Is needed!
Heat is Different from Temperature
• Do Not Confuse the
them!
• Temperature is the
measure of the
average kinetic
energy of all the
particles in an object.
• HEAT: flow of
energy from higher
to lower
temperature (51)
Flow of Energy
• Ice Cube in a bowl- At first different
temperatures then they have the same
temperature.
• Energy flows from the particles in the warmer
bowl to the particles in the cold ice and, later, the
cooler water.
• If energy flowed the opposite direction—from
cooler to warmer---the ice would get colder in
the bowl and bowl would get hotter!
THAT NEVER HAPPENS!
Thermal Energy
• When energy flows from a warmer object
to a cooler object, the thermal energy of
both of the objects changes.
• Thermal Energy- the total random kinetic
energy of particles in an object.
Measuring Heat
• The most common unit of heat
measurement are the calorie and the joule
• One calorie is the amount of energy
needed to raise the temperature of 1
gram of water by 1°C. (54)
• The joule (J) is the standard scientific unit
in which energy is measured.
• One calorie is equal to 4.18 joules.
Calorie or calorie?
• Calorie with a big “C” is referring to
nutrition. It is actually one kilocalorie or
1000 calories.
• This means that 1 Calorie in food contains
enough energy to raise the temperature of
1 kilogram of water by 1°C.
• So, each Calorie in food contains 1000
calories of energy.
Calorimeter
• How do we know how many Calories are
in a food?
• We use a calorimeter to see how much
energy is released through heat.
Some Substances Change
temperature more easily than others
Specific Heat
• The amount of energy required to raise
the temperature of 1 gram of a
substance by 1°C is the specific heat
value. (57)
• So, each substance absorbs a different
amount of energy in order to show the
same increase in temperature.
• Page 113 (Graph)
Do You Know?
• 1) Which of these substances has the
highest specific heat?
•
(a) Sample A
•
(b) Sample B
•
(c) Sample C
•
(d) Sample D
Answer: A
Specific Heat and Mass
• Thermal energy depends on the object’s
mass.
• Which mass of water has more thermal
energy?
Review
• How is temperature related to heat?
– Heat transfers energy because a temperature
difference exist.
What units do we use to measure heat?
Calorie and Joule
Describe specific heat
The amount of energy that 1 gram of a
substance needs to absorb to increase in
temperature by 1°C.
Energy Moves as Heat in Three
Ways
• Conduction
• Convection
• Radiation
Conduction
• The process that
moves energy from
one object to another
when they are
touching physically.
Conductors (60)
• Some materials
transfer the kinetic
energy of particles
better than others.
• Conductors are
materials that transfer
energy easily.
• The pot handle is a
poor conductor
Insulators (61)
• Materials that conduct heat slowly or poorly are
called insulators
• Glass, wood, plastic and rubber are poor
conductors (good insulators)
• Nearly all liquids including water are poor
conductors (good insulators)
• Gases, including air are poor conductors,e.g.,
wool feels warm because it traps a lot of air
• A fridge has insulation material round it to keep it
cold – reduces amount of heat conducted to
inside from the warmer room
Convection (60)
• Convection is the movement of gases or liquids
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. The cooler soup then moves to take
the warmer soup's place. The movement is in a
circular pattern within the pan (see picture
above).
Convection Cycle
1. Warmer, less dense
air is pushed up by
cooler, denser air.
2. When air cools, it
becomes more dense
and starts to sink.
3. Sinking air moves
under warmer air,
pushing it upward.
Radiation (60)
• The energy that
travels as
electromagnetic
waves which include
visible light,
microwaves, and
infrared light.
• When radiation from
the Sun is absorbed,
energy is transferred
through heat.
Insulators
• Energy is always being transferred
between objects at different temperatures.
• Insulators are used to control and slow the
transfer of energy from warmer to cooler
objects.
• Insulators work by trapping the energy.
Insulators
Heat Transfer
• Conduction: energy moves
from one object to another by
physically touching
• Convection: energy transfers
by the movement of large
numbers of particles in the
same direction with in a liquid
or gas
• Radiation: energy that travels
through electromagnetic wave
• Insulator: poor conductors
4.3 Review
• What are 3 ways energy can be
transferred through heat?
– Convection, conduction, radiation
How are conductors and insulators
different?
Conductors easily transfer energy, but
insulators do not.