Download Energy - chappellscience

Nature of Energy
• Energy is all around you!
o You can hear energy as sound.
o You can see energy as light.
o You can feel it as wind and
heat.
•
You use energy when you:
o hit a softball.
o lift your book bag.
o compress a spring.
o Burn fuel
States of Energy:
Kinetic and Potential Energy
• Kinetic Energy is the energy
of motion.
• Potential Energy is stored
energy of position or
chemical bonds.
Nature of Energy
• Energy is
involved when:
o a bird flies.
o a bomb
explodes.
o rain falls from
the sky.
o electricity flows
in a wire.
Kinetic Energy
• The energy of motion is called kinetic
energy.
• The faster an object moves, the
more kinetic energy it has.
• The greater the mass of a moving
object, the more kinetic energy it
has.
• Kinetic energy depends on both
mass and velocity.
Kinetic Energy
K.E. = ½ mass x velocity2
What has a greater affect of kinetic
energy, mass or velocity? Why?
Potential Energy
• Potential Energy is stored energy.
o Stored chemically in bonds of fuel or food
o Stored as nuclear energy holding
subatomic particles together
o Or stored because of the work done on it:
• Stretching a rubber band.
• Winding a watch.
• Pulling an arrow back on a bow’s string.
• Lifting a brick high in the air.
Gravitational Potential Energy
• Potential energy
dependent on
height is called
Gravitational
Potential Energy
(a form of mechanical
energy)
Gravitational Potential Energy
• If you stand on a 3meter diving board, you
have 3 times the G.P.E,
than you had on a 1meter diving board.
• GPE=Weight x Height
•
•
or
(pounds)
(Newtons)
x
x
(feet)
(meters)
• GPE = (M)(Ag) (H)
•
M=Kg, Ag =9.8m/sec2,H=m
Kinetic – Potential
Energy Conversion
Cars are mechanically pulled to the peak which is the point of maximum
potential energy, the car has minimum kinetic energy. As position is
exchanged for speed, potential is converted to kinetic energy.
Ball speeds up
Ball slows down
Forms of Energy
• The five main forms of energy are:
oHeat
oChemical
oElectromagnetic
oNuclear
oMechanical
Heat Energy
• The internal motion of the atoms is
called heat energy, because
moving particles produce heat.
• Heat energy can be produced by
friction.
• Heat energy causes changes in
temperature and phase of any
form of matter.
Chemical Energy
• Chemical Energy is required to
bond atoms together.
• And when bonds are broken,
energy can be released or
absorbed
• Exothermic = energy released.
• Endothermic=energy absorbed.
Chemical Energy
• Fossil Fuels and our Food
are forms of energy stored
in chemical bonds
• The Energy came from nuclear fusion
on our Sun and was photosynthesized
by plants and stored in plant and
animal life
Formation of Fossil Fuels
• Petroleum and Natural gas are
both products of millions of
years of decomposing Marine
life, both animal and plant
• Coal is similar but mostly from
terrestrial plant life
Where does Coal come from?
Electromagnetic Energy
• Electricity -- carried in wires
• Light -- Each of the colors of
light (ROY G BIV) represents a
different amount of
electromagnetic energy
• X-rays & Cosmic Rays
• TV & Radio waves
• Laser light.
Nuclear Energy
• When the nucleus splits
(Fission), nuclear
energy is released in
the form of heat energy
and light energy.
• Nuclear energy is also
released when nuclei
collide at high speeds
and join (Fusion).
• MOST CONCENTRATED
Mechanical Energy
• When work is done to an
object, it acquires energy.
The energy it acquires is
known as mechanical
energy.
Mechanical Energy
• When you kick a
football, you
give mechanical
energy to the
football to make
it move.
Energy Conversion
• Energy can be changed
from one form to another.
Changes in the form of
energy are called energy
conversions.
• Good Examples on Pages
418-419
Energy conversions
• All forms of energy can be converted
into other forms.
o The sun’s energy through solar cells
can be converted directly into
electricity(Photovoltaic energy).
o Green plants convert the sun’s
energy (electromagnetic) into the
bonds in starches and sugars
(chemical energy) using
Photosynthesis.
Other energy conversions
o In an electric motor,
electromagnetic energy is
converted to mechanical
energy.
o In a battery, chemical energy is
converted into electromagnetic
energy.
o Mechanical energy of water
falling can be converted to
electrical energy in a generator.
Hydroelectric Power
Forms of Alternative Energy
Energy Conversions
• In an automobile
engine, fuel is
burned to convert
chemical energy
into heat energy.
The heat energy is
then changed into
mechanical
energy.
Chemical  Heat Mechanical
The Law of Conservation of
Energy
• Man can neither create nor
destroy Energy by ordinary
means.
oIt can only be converted from one
form to another.
oIf energy seems to disappear, then
scientists look for it – leading to
many important discoveries.
Law of Conservation of
Energy
• In 1905, Albert Einstein said that mass and
energy can be converted into each other.
• He showed that if matter is destroyed,
energy is created, and if energy is
destroyed, mass is created.
• E=MC2
• M=mass C=speed of light
Power = measure of Energy
•
•
•
•
Work = Force x Distance
Rate of doing Work or
Amount of Work/unit of time
Power= Work/Time
• Power = (Force x Distance)/Time
•
•
•
•
Power Units = Watts
1Watt=1Joule/sec or (1N*m/sec)
1 Kilowatt = 1000 watts
1 Horsepower = 746 watts
Thermal Energy
(Heat) differs from
Temperature
Heat vs. Temperature
• Heat content is the TOTAL KINETIC
ENERGY of the particles in a
sample
• Temperature is the AVERAGE
KINETIC ENERGY of the particles
in a sample
Which has more Heat and which
has the highest temperature?
Insulators
• There are
thousands of
air bubbles
trapped in the
styrofoam
which slows
down the heat
flow through
the layer
Insulation:
How do the Polar
Bears stay warm in
the snow? Their
dense, fine fir traps
an air layer next to
their skin.
Home Insulation
• The pink fiberglass
fibers trap air in the
mat of insulation
preventing heat
from escaping in
the winter or heat
from entering during
the summer.
Insulation
Highly Insulating
Windows
• Two or three panes between inside and outside air
• Insulation is supplied by the Dead Air Space
Image source: Southwall
Technologies
Heat Transfer
• Occurs three ways
oConduction
oConvection
oRadiation
• The transfer of heat by
direct contact
between objects or
particles.
• Motion of solid atoms
or molecules carried
from particle to
particle
• Heat transferred by the movement of
molecules within liquid or gaseous
substance.
• Warm rises, cool sinks.
• A circular motion begins from warmer
areas rising due to decreased density
moving toward cooler areas which fall
because of increased density.
• Wind and Major Weather patterns are
caused and move largely because of these
convection currents.
• Heat transferred through
space
• MATTER is not
needed
for radiation
• EXAMPLE: The sun’s rays
carrying visible light and
UV light causing sunburn.
Radiation
• Transfer of heat through
electromagnetic radiation
(light from stars or light bulbs).
• Transferred in all directions.
• Matter is not required!
• Dark or dull objects absorb
more than light or shiny
objects do.
Temperature
• Temperature is a
measure of the
average KE of the
particles in a
sample of matter
Temperature
Conversions
• oC to oF: oF = (9/5)oC + 32
• oF to oC: oC = 5/9(oF – 32)
o
o
• C to K: K = C + 273
o
o
• K to C:.
C = K – 273
Going from Celsius to Fahrenheit
oC
Convert 37
to
oF = (9/5)oC + 32
oF = (9/5)37oC + 32
= 66.6 + 32
= 98.6oF
oF.
Going from Fahrenheit to Celsius
Convert 68oF to oC
oC = 5/9(oF – 32)
oC = 5/9(68 – 32)
= 5/9(36)
= 20 oC
Going from Kelvin to Celsius
Convert 310 K to oC
oC = K – 273
oC = 310 – 273
= 37oC
Thermal Energy
• Which beaker of water has more thermal
energy?
o B - same temperature but more mass
80ºC
A
80ºC
B
200 mL
400 mL
Thermal energy relationships
a. As temperature increases, so does thermal
energy (because the kinetic energy of the
particles increased).
b. Even if the temperature doesn’t change,
the thermal energy in a more massive
substance is higher (because it is a total
measure of energy).
c. Energy always travels from a high
concentration(warm) to a lower
concentration(cool) of heat.
Land heats up and cools down faster than water.
The temperature of the water helps keep the land
temperature stable.
Thermal Expansion
• Additional heat content causes matter to expand.
• Loss of heat content causes matter to contract.
• Faster particles take up more space.
Sample Problem:
Thermal Expansion
• What will be the new volume of 200ml of
20°C water if the temperature is raised to
90°C.
• ∆V = 3σ · ∆T · Vo
•
= 3 x 69e-6/°C x 70°C x 200ml
•
= 2.898ml
• Vnew = Vold + ∆V
• Vnew = 200ml + 2.898ml = 202.898ml
Specific heat(CH O) is the amount of
heat required to raise the temperature
of 1 kg of a material by one degree
(C° or K).
2
1) C(H O)
2
= 4184 J / kg C°
= 4.18 kJ / kg C°
2) C(sand) = 664 J / kg C°
This is why land heats up quickly
during the day and cools quickly at
night and why water takes longer.
How to calculate changes
in thermal energy
Q = m x Cp x T
Q = quantity of thermal energy
m = mass of substance
T = change in temperature (Tf – Ti)
Cp = specific heat of substance(p)
Heat Transfer

How much heat is required to warm
230 g of water from 12°C to 90°C?
GIVEN:
m = 230 g
Ti = 12°C
Tf = 90°C
Q=?
C(H O)= 4.184 J/g·oC
2
WORK:
Q = m·T·Cp
m = 230 g
T = 90°C - 12°C = 78°C
Q = (230g)(78˚C)(4.184 J/g·oC)
Q = 75,061 J
Calorimeters are used to measure
the specific heat of a substance.
Professional
King’s Ridge
Phase Change Diagram
• If constant heat is added to a substance, one of
two things can happen: a. temperature rise or
b. change of state
• A: Temperature change
of a solid
• B: Melting
• C: Temperature change
of a liquid
• D: Vaporization
• E: Temperature change
of a gas
Laws of Thermodynamics
• First Law: Energy is always conserved.
o Energy added to a system may do two things
• Increase the total thermal energy of the system
• Do work on the system
o Example: Bicycle Pump puts air into tire(work) and heats the
air(thermal)
• Second Law: Heat can travel from cold to hot ONLY if work is
done on the system.
o Example: The compressor in a refrigerator
• Third Law: We will never reach Absolute Zero
Uses of Heat
• Heat Engines
o External Combustion Engines: Fuel is burned outside of the
engine
• Steam Engine
Internal Combustion
o Internal Combustion Engines: Fuel is burned inside of the engine
• Car engines
o 4 stroke engine: Pistons moving up/down/crankshaft turning
• Intake: moving down, intake valve open, fuel mixture drawn in
• Compression: moving up, both valves closed
• Power: moving down, both valves closed, spark igniting fuel
• Exhaust: moving up, exhaust valve open, waste exits
o Cooling system: to keep the temperature of the engine within a
specific range to prevent damage
o Electrical system: Battery is used to start the engine then
alternator used to produce the electricity needed to run the engine,
charge battery and all other systems such as air conditioning.
Heating Systems
•
•
•
•
Hot-Water Systems—boilers and radiators -full of hot water
Steam Heat Systems-“
-full of hot steam
Electric Heat Systems—producing heat(lightbulb)
Forced Air Heating Systems—most homes todaym, burning a fuel
and blowing the warmed air around
• Solar Heating: using sunlight to heat water and homes
o Passive—allowing sunlight to enter home most efficiently and
trapping it
o Active—collecting solar energy then heating the home with the
energy
• Heat Pumps: evaporators, condensers & coolant
o Home Heating—drawing heat from the warm earth
o Refrigerator—drawing heat from the warm food and warm air
o Air Conditioner—drawing heat from the warm room