Transcript Energy and Heat Transfer PPTx

Energy Notes
What is Energy?
Energy makes change. Energy moves
cars along the road and boats over
the water. It bakes a cake in the oven
and keeps ice frozen in the freezer. It
plays our favorite songs on the radio
and lights our homes. Energy makes
our bodies grow and allows our
minds to think. Scientists define
energy as the ability to do work.
People have learned how to change
energy from one form to another so
that we can do work more easily and
live more comfortably.
Forms of Energy
Energy is found in different forms, such as light, heat,
sound and motion. There are many forms of energy, but
they can all be put into two categories: kinetic and
potential.
KINETIC ENERGY
POTENTIAL ENERGY
Kinetic energy is motion— Potential energy is stored
of waves, electrons, atoms, energy and the energy of
molecules, substances, and
position (gravitational
objects.
energy).
Electrical energy is the movement of
electrical charges. Everything is made of
tiny particles called atoms. Atoms are made
of even smaller particles called electrons,
protons, and neutrons. Applying a force can
make some of the electrons move. Electrical
charges moving through a wire is called
electricity. Lightning is another example of
electrical energy.
Radiant energy is electromagnetic energy
that travels in transverse waves. Radiant
energy includes visible light, x-rays, gamma
rays and radio waves. Light is one type of
radiant energy. Solar (sun) energy is an
example of radiant energy.
Thermal energy, or heat, is the internal
energy in substances––the vibration
and movement of the atoms and
molecules within substances. Geothermal energy is an example of
thermal energy.
Motion energy is the movement of
objects and substances from one
place to another. Objects and
substances move when a force is
applied according to Newton’s Laws
of Motion. Wind is an example of
motion energy.
Sound is the movement of energy through
substances in longitudinal
(compression/rarefaction) waves. Sound is
produced when a force causes an object or
substance to vibrate––the energy is
transferred through the substance in a
wave.
To sum up what happens to energy when you use a phone to call a friend:
1. The sound energy in your voice makes the air vibrate. Vibrating air carries the sound
energy into the phone. 2. The diaphragm in the mouthpiece microphone converts
sound energy into electrical energy. 3. The electrical energy travels from the phone, via
exchanges, to your friend's phone. 4. A diaphragm in the earpiece loudspeaker of your
friend's phone converts the incoming electrical energy back to sound energy. 5. The
sound energy travels out from the earpiece into your friend's ear.
Chemical energy is energy stored in
the bonds of atoms and molecules.
It is the energy that holds these
particles together. Biomass,
petroleum, natural gas, and propane
are examples of stored chemical
energy. Ex. H-O-H
Elastic (Mechanical) energy is energy stored in objects by the
application of a force. Compressed springs and stretched rubber
bands are examples of stored mechanical energy.
Nuclear energy is energy stored in the nucleus of an atom––the
energy that holds the nucleus together. The energy can be released
when the nuclei are combined or split apart. Nuclear power plants
split the nuclei of uranium atoms in a process called fission. The sun
combines the nuclei of hydrogen atoms in a process called fusion.
Scientists are working on creating fusion energy on earth, so that
someday there might be fusion power plants.
Gravitational energy is the energy of position or place. A rock
resting at the top of a hill contains gravitational potential energy.
Hydropower, such as water in a reservoir behind a dam, is an
example of gravitational potential energy.
Law of Conservation of Energy
Conservation of energy
is NOT saving energy.
The law of conservation
of energy says that
energy is neither created
nor destroyed. When we
use energy, it doesn’t
disappear. We change it
from one form of energy
into another.
A car engine burns gasoline, converting the chemical energy
in gasoline into mechanical energy. Solar cells change
radiant energy into electrical energy. Energy changes form,
but the total amount of energy in the universe stays the
same.
Energy Efficiency
Energy efficiency is the amount of useful energy you get from a
system. A perfect, energy-efficient machine would change all the
energy put in it into useful work—an impossible dream. Converting
one form of energy into another form always involves a loss of
usable energy.
In fact, most energy
transformations are NOT very
efficient.
The human body is a good example.
Your body is like a machine, and the
fuel for your machine is food. Food
gives you the energy to move,
breathe, and think. But your body
isn’t very efficient at converting
food into useful work. Your body is
less than five percent efficient most
of the time. The rest of the energy
is lost as heat. You can really feel
that heat when you exercise!
What Does Energy Mean to Us?
All organisms must have energy to survive. Photosynthesis is the
chemical process that provides that energy! During photosynthesis, the
sun’s energy is trapped in the chemical bonds of glucose. Plants
(producers) provide us with ENERGY!
PHOTOSYNTHESIS
Energy Conversion: RADIANT ENERGY is CONVERTED TO CHEMICAL ENERGY!
6CO2 +
6H2O
carbon dioxide water
+
ENERGY
 C6H12O6 +
from sunlight
glucose
6O2
oxygen
CELLULAR RESPIRATION
C6H12O6 +
glucose
6O2
oxygen

6CO2
carbon dioxide
+
6H2O + ENERGY
water
ATP
CHEMICAL ENERGY IS CONVERTED INTO ATP –
bioCHEMICAL ENERGY!
RESPIRATION
During cellular RESPIRATION the energy is released from it’s
chemical bonds for use by the cells. The usable energy form is called
ADENSOSINE TRIPHOSPHATE (ATP).
Conversions efficiencies are always much less than 100%. At each
link in a food chain, a substantial portion of the sun's energy originally trapped by a photosynthesizing autotroph - is dispersed
back into the environment (ultimately as heat). Our bodies convert
only about 35% of the energy that it takes in. This may seem
inefficient, but our cars are even less efficient. Cars convert about
25% of its energy intake into motion.
Sources of Energy
We use many different energy sources to do work for us.
Energy sources are classified into two groups—renewable
and nonrenewable. Renewable and nonrenewable energy
can be converted into secondary energy sources like
electricity and hydrogen.
In the United States, most of our
energy comes from nonrenewable
energy sources. Coal, petroleum,
natural gas, propane, and uranium
are nonrenewable energy sources.
They are used to make electricity, to
heat our homes, to move our cars,
and to manufacture all kinds of
products.
These energy sources are called
nonrenewable because their supplies
are limited. Petroleum, for example,
was formed millions of years ago
from the remains of ancient sea
plants and animals. We can’t make
more petroleum in a short time.
Renewable energy sources
include biomass,
geothermal energy,
hydropower, solar energy,
and wind energy. They are
called renewable energy
sources because they are
replenished in a short time.
Day after day, the sun
shines, the wind blows, and
the rivers flow. We use
renewable energy sources
mainly to make electricity.
Energy Calculations
The S.I. unit for energy is Joules, J.
Kinetic Energy = 1/2 mass X velocity2
KE = mv2/ 2
Example Problem:
A 15 kg bicycle carrying a 50 kg boy is traveling at a speed of 5 m/s.
What is the kinetic energy of the bicycle (including the boy)?
Gravitational Potential Energy = mass X acceleration due to gravity X height
PE = mgh
Example Problem:
A 0.06 kg tennis ball starts to fall from a height of 2.9 m. How much
gravitational potential energy does the ball have at that height?
Example Problem:
Thomas is holding a tennis ball outside
a second floor window (3.5 m from the
ground) and Dustin is holding one
outside a third floor window (6.25 m
from the ground). How much more
gravitational potential energy does
Dustin’s tennis ball have? (Each tennis
ball has a mass of 0.06 kg.)
Mechanical Energy = potential energy + kinetic energy
joules
potential
energy
kinetic
energy
friction
nuclear
fusion/fission
Thermal Energy
All matter is made of tiny particles—atoms and molecules. In all
materials—solids, liquids, and gases—these particles are in constant
motion. Like all objects that are moving, these moving particles have
kinetic energy. The faster these particles move, the more kinetic
energy they have.
The temperature of an object is related to the average kinetic energy
of the atoms or molecules. The faster these particles are moving, the
more kinetic energy they have, and the higher the temperature of the
object is. The SI unit for temperature is Kelvin (K).
The sum of the kinetic and potential energy of all the molecules in an
object is the thermal energy of the object.
***Heat is thermal energy that flows from something at a
higher temperature to something at a lower
temperature. Heat is a form of energy, so it is
measured in joules—the same units that energy is
measured in. Heat always flows from warmer to cooler
materials.
The amount of heat that is needed to raise the temperature of 1 kg
of some material by 1°C or 1 K is called the specific heat of the
material. Specific heat is measured in joules per kilogram Kelvin
[J/(kg K)].
Q = mc∆T
Q = thermal energy
m = mass
c = specific heat of substance
∆T = change in temperature
SPECIFIC HEAT CALCULATIONS
Q = mc∆T
1. If 150 kilograms of water is heated from 30oC to 40oC, the
number of joules of heat energy absorbed is…
2. If a 2.0 kg sample of water at 5.0oC absorbs 26 J of heat energy,
the temperature of the sample will be…
HEAT TRANSFERS BY:
Conduction—the movement of thermal energy from
one object to another when they are in direct contact
(touching). Molecules can transfer energy to a
neighboring one within an object.
Examples:
• Bare feet touching the cement on a hot summer day
• Warming up with a hot cup of coffee
• Car seat warmers
Can you think of any other examples???
Convection—the movement of thermal energy from one
area to another in a liquid or gas. Heat transfers by
currents.
Examples:
• Wind Currents
• Hot Air Balloon
Can you think of any other examples?
Radiation—when warm or hot matter emits
electromagnetic radiation – especially infrared radiation –
that is then absorbed by an object at a distance. The
absorption heats the second object. This energy transfer
does NOT require matter.
Examples:
• A microwave oven
• The Sun
• UV light
Can you think of any other examples?
http://soundcloud.com/educationalrap/sets/radiation-conduction-convection
Controlling Heat Flow
Almost all living things have special features that help them control the flow of
heat. For example, the Antarctic fur seal’s thick coat and the emperor penguin’s
thick layer of blubber help keep them from losing heat. This helps them survive in a
climate in which the temperature is often below freezing. In the desert, however,
the scaly skin of the desert spiny lizard has just the opposite effect. It reflects the
Sun’s rays and keeps the animal from becoming too hot. An animal’s color also can
play a role in keeping it warm or cool. The black feathers on the penguin’s back, for
example, allow it to absorb as much radiant energy as possible. How do you think
humans control body heat flow?
Insulators—a material that does NOT allow heat to flow
through it easily. Materials such as wood, plastic,
fiberglass, and air are good insulators. Gases are usually
much better insulators than solids or liquids.
Conductors—a material that allows heat to flow through
it easily. Although conduction can occur in solids, liquids,
and gases, solids usually conduct heat much more
effectively. Metals such as silver, copper, and aluminum
are among the best heat conductors.
A material that is a good conductor of heat, such as a metal, is a
poor insulator. Likewise, good insulators are poor conductors of
heat. Why do you think most cooking pots are made of metal but
the handles usually are not?
Heat Movers—a device that removes thermal energy from
one location and transfers it to another location at a
different temperature such as a refrigerator and air
conditioner.
3.Change in Energy :
• Endergonic Reaction—energy is absorbed; requires more
energy to break bonds than is given off when new bonds are
formed
Endothermic Reaction—absorb heat from surroundings
Ex: Commercial cold packs usually consist of two compoundsurea and ammonium chloride in separate containers within a
plastic bag. When the bag is bent and the inside containers are
broken, the two compounds mix together and begin to react.
Because the reaction is endothermic, it absorbs heat from the
surrounding environment and the bag gets cold.
• Exergonic Reaction—energy is released; less energy is
required to break the original bonds than is released
when new bonds form
Exothermic Reaction—giving off heat or light release
energy to the surroundings (usually in the form of heat)
Ex: sodium and chlorine react so violently that flames
can be seen as the exothermic reaction gives off heat.