Transcript Energy / Thermodynamics (Heat)

Energy / Thermodynamics (Heat)
I. Energy:
A. The ability of an object to produce change in the
environment or in itself.
B. Types: kinetic vs. potential (gravitational/elastic)
C. Many forms including: thermal, light, electrical,
chemical, nuclear, electromagnetic, solar,
mechanical (sum of kinetic & potential)
D. Energy can be transferred from one form to
another.
E. Energy is conserved (law of conservation)
II. Work: transfer of energy through motion. (It is zero
work if object doesn't move.)
A. Work involves Force and Displacement (movement,
change in position).
B. Formula: W = F x d (work = force (wt) x
displacement)
C. Work units are Nm (Newton-meters) OR J (Joules)
III. Simple Machines: Tools that enable (F) & (d) to be
varied while keeping work constant.
A. Can reduce (F) by increasing (d) through which force
is exerted.
B. Examples:
1. Inclined plane
5. Wedge
2. Lever
6. Screw
3. Pulley
7. Block & tackle
4. Wheel & axle
IV. Friction – force opposing motion, energy used to
overcome friction changes to heat.
V. Power: rate at which work is done, measure of the
amount of work done in a certain amount of time.
A. Calculated by P = W/t
B. Units are in watts (W) {1W=1 Joule/second}
.
VI. Chemical potential energy: food
A. Food is the energy (chemical PE) our bodies
need to help our bodies do work (KE).
B. A food Calorie (measures energy from food) is
equal to 1 kilocalorie  4180 J)
VII. Thermal Energy / Heat (thermodynamics)
A. The transfer of energy from a higher
temperature body to a lower temperature body.
B. Involves: Energy transfer and Energy
conservation
VIII. Molecular Kinetic Energy (KE) and Temperature (temp).
A. All molecules have KE.
1. The more energy molecules absorb, the greater
their KE.
2. Ex: Hot water has more KE than cold water.
B. Temperature-a measure of the average KE of
molecules.
1. The faster the molecules move, the higher the temp.
2. Temp. Scales – most countries use the Centigrade
(Celsius) scale.
a. Centigrade (Celsius)- C, water boils at 100C,
water freezes at 0C
b. Fahrenheit -F, water boils at 212F, water
freezes at 32F
c. Kelvin-(K): A thermodynamic Celsius temp.
scale used to measure extreme temp.
(1.) 0 Kelvin = -273C or -460F
(2.) Absolute Zero or 0 Kelvin (K) – molecules
have the lowest KE possible.
IX. Energy Transfer-three types:
A. Conduction
B. Convection
C. Radiation
X. Energy Transfer Within a body
A. Conduction: molecules transfer energy by
physical (direct) contact.
1. Solid molecules easily make contact because
they are close together.
2. Solids are good conductors of heat.
3. Liquids are poorer conductors of heat because
molecules are farther apart.
4. Gases are the poorest heat conductors because
molecules hardly ever make contact.
B. Convection: molecules transfer
energy by carrying it from one place to
another (Ex: liquids and gases when heat
rises.)
1. Gas & liquid molecules transport energy
if movement is unrestricted.
2. Air is not a good conductor, but it is
ideal for convection. Hot air rises by
convection.
3. Convection currents-streams of hot air
(ideal for gliding) or streams of warm
water (in the ocean).
XI. Energy Transfer Between bodies:
A. Conduction between bodies: molecules in one body
contact molecules in another body and transfer energy.
(Ex: Hot soup to a spoon in the soup).
B. Radiation: Energy transferred without direct contact. (Ex:
sun’s or light rays)
1. When radiant energy is absorbed, molecules move
faster & temp. rises.
2. Infrared radiation (invisible light) – all objects
give off some amount of this type of radiant energy.
3. Some hot objects give off radiation in the form of
visible and invisible light (Ex: hot stove-light is seen
and heat is felt).
C. Note: energy transfer between bodies occurs by
conduction & radiation.
XII. Insulators – make energy transfer difficult
A. Insulation against conduction:
1. Makes molecular contact difficult.
2. A poor conductor (air) makes a good
INSULATOR.
3. Examples:
a. Styrofoam – pockets of air limit
conduction.
b. Space shuttle tiles – help shuttle
withstand heat from re-entry to Earth.
c. Fur / feathers trap air for insulation.
B. Insulation against convection:
1. Stops molecular movement from one place to
another.
2. Examples: windows, doors, weather-stripping.
C. Insulation against radiation:
1. Block light rays.
2. Examples:
a. Light or shiny materials reflect radiation.
b. Dark or dull materials absorb radiation.
c. Ozone insulates Earth from UV rays by
absorbing them.
D. Insulation limits transfer of energy between bodies.
Ex: Wet suits limit energy transfer from a warm
body to the cold water.
E. Insulation limits transfer of energy within a body. Ex:
Windows limit energy transfer from warm to
cold air.
XIII. Heat vs. Temperature
A. Heat – the amount of energy transferred
between 2 groups of molecules at different
temperatures.
B. Temperature – the measure of motion
(KE) of a typical molecule within a body
of matter.
C. Heat Flow:
1. Heat flows from a higher temperature
body to a lower temperature body.
2. Heat flows between objects in contact
ONLY when a difference in temperature
exists.
3. If 2 hot objects come into contact, heat
will NOT flow between them IF they have
the same temperature.
D. Specific Heat – the amount of heat required
to change a unit mass of a substance by one
degree of temperature. (The amount of heat
needed to change temperature by a certain
amount.)
1. How difficult something is to heat or to
cool.
2. A long heating time indicates a long cooling
time.
3. Substances with a high specific heat are harder to
heat. (Ex: water)
4. Substances with a low specific heat are easier to
heat. (Ex: silver)
E. Remember: Energy lost = Energy gained (Law of
Conservation of Energy)
XIV. Calculating Heat Energy
A. Heat can be measured in calories or joules
( 1 cal = 4.18 J ). A nutritional calorie = 1
kcal = Calorie.
B. Remember specific heat (heat capacity)
has to do with the ability to absorb heat
energy.
C. Formula: Heat (J of energy gained/lost) =
mass (grams) x change in temp(C) x
specific heat (J/gC)
H = m x T x Cp
XV. Heat / Phase Change
A. Phase change occurs when
substances change state.
B. Phase changes require energy. As
more heat is added, temperature does
NOT increase, instead that thermal
energy goes into breaking the bonds as
it changes state. (See graph at **)
C. Heat of fusion: solid to a liquid.
D. Heat of vaporization (liquid to a gas).
E. Refer to graph.
XVI. Earth Science Applications:
A. Sun Energy-air/water patterns / relationships:
1. Differences between climate and weather
2. Global climate/warming, greenhouse
effect
3. El Nino, La Nina, and other climatic
trends.
4. Temperature effects on ground water
B. Earth’s internal structure (core, mantle, crust)
1. Convection as mechanism for plate tectonics
2. Geological manifestations (plate tectonics,
earthquakes, volcanoes, mountain building)
3. Impact on society
C. Characteristics/Evolution of Earth in terms of
age (rock sequences, fossils,
relative/radiometric dating) and the geosphere,
hydrosphere, atmosphere, and biosphere