Download (eg , heat transfer, energy conversion) in a system.

UNDERSTAND PRINCIPLES AND CONCEPTS
RELATED TO ENERGY
At this level, students should be introduced to energy primarily through energy transformations.
Students should trace where energy comes from (and goes next) in examples that involve several
different forms of energy along the way: heat, light, motion of objects, chemical, and elastically
distorted materials. To change something's speed, to bend or stretch things, to heat or cool them, to
push things together or tear them apart all require transfers (and some transformations) of energy.
Food, gasoline, and batteries obviously get used up. But the energy they contain does not disappear;
it is changed into other forms of energy.
Identify forms (e.g. mechanical, chemical) and types (e.g., potential, kinetic) of
energy and their characteristics.
MEMORIZE
1. Friction is not energy. Friction is a force.
2. Energy is the ability to do work or supply heat.
3. Work is heat and heat is work. Work is the transfer of energy to move
an object.
4. Heat is not a form of energy but a method of transferring energy.
FIRST LAW OF THERMODYNAMICS – Energy is neither created nor destroyed. Energy is merely
transformed or changed from one form to another.
SECOND LAW OF THERMODYNAMICS – Heat can’t pass from a colder to a hotter body. And no machine
is 100% efficient. Some heat is lost to the environment and some sound is lost.
TWO TYPES OF ENERGY - Potential (Position, An object’s energy stored in matter due to position
relative to other objects). Kinetic (Moving, the energy of a moving object). A football in the air has both
types of energy.
KE = ½(m times v times v) or ½ mas times velocity squared.
PE = m times g times h. mass of the object times the gravitational pull on the object times the height
of the object.
Mechanical energy is the total potential plus the total kinetic energy.
THE ELEPHANT WITH A “P” ON HIS SWEATER JUMPS OFF A CLIFF.
Potential
G - Gravitational
E - Elastic
N – Nuclear (energy in atoms nucleus)
C – Chemical (energy in chemical bonds)
Kinetic
M - Mechanical
E – Electric (moving electrons)
R – Radiation or EM
T – (Thermal or heat)
S – Sound.
Common Energy Transformations
1. Different types of stoves are used to transform chemical energy of fuel (gas, coal, wood, etc.)
into heat. Heat can then make water into steam and turn turbines to make electricity.
2. Solar collectors can be used to transform solar energy into electrical energy.
3. Windmills make use of the kinetic energy of the air molecules, transforming it into mechanical
energy that turns turbines to make electrical energy.
4. Hydroelectric plants transform the kinetic energy of falling water into electrical energy.
5. A flashlight converts chemical energy stored in batteries to light energy and heat. Most of the
energy is converted into heat, only a small amount is changed into light energy.
Demonstrating knowledge of energy transformation and transfers (e.g. , heat
transfer, energy conversion) in a system.
A slightly more sophisticated proposition is the semi-quantitative one that whenever some energy
seems to show up in one place, some will be found to disappear from another. Eventually, the energy
idea can become quantitative: If we can keep track of how much energy of each kind increases and
decreases, we find that whenever the energy in one place decreases, the energy in other places
increases by just the same amount.
The energy that is transferred into or out of a system is heat transfer.
In a closed system, if one substance loses heat then another substance must gain heat.
Heat of fusion is the amount of heat it takes to change from a solid to a liquid or the loss of
energy in going from a liquid to a solid.
Latent heat – The heat that is required to change a substance from one state to another.
Heat of vaporization – the amount of heat that it takes to change from a liquid to a gaseous
state.
Convection is not so much an independent means of heat transfer as it is an aid to transfer of heat
by conduction and radiation. Convection currents appear spontaneously when density differences
caused by heating (conduction and radiation) are acted on by a gravitational field.
Medium needed
How many substances
or mediums
Travel in Outer space
Conduction
Yes
Convection
Yes
Radiation
No
2 or more
No
1 one
No
None
Yes
Heat travels through
a heated solid or
between two heated
solids that are
touching
Heat travels through
a fluid (air or liquid)
because of changing
density. Warm fluids
have a larger volume
as molecules move
faster and farther
apart so they are less
dense.
Heat transfer as the
result of
electromagnetic
waves of traveling
photons. The sun
warms the earth by
emitting radiant
energy. Photons are
packets of energy.
Applying knowledge of the gas laws (e.g. Boyle’s law and Charles’s law).
The behavior of gases—such as their compressibility and their expansion with temperature—may
be investigated for qualitative explanation; but the mathematics of quantitative gas laws is likely to
be more confusing than helpful to most students.
PRESSURE is the force exerted on each unit of area of a surface. Pressure is measured in a unit called
Pascal.
Temperature, Pressure, and Volume are related.
Temperature
Boyle’s Law
Charles’s Law
No Change
If temperature goes up
Pressure
If Pressure goes up
No Change
If temperature goes
Then Pressure goes
up. A tire on a hot day up because volume
or a steel pressure
does not change.
cooker.
Volume
Volume goes down.
Think of a squeezed
balloon.
Then volume goes up.
Think of the balloon
Amber in a hot car.
No Change.
Thermometers are an example of a one object with a constant volume (thermometer) and one
with a changing volume (alcohol or mercury inside). When the temperature goes up, the liquid
expands inside because the volume does change.
Analyzing phase diagrams (e.g., heat versus temperature) and the flow of
energy during changes in states of matter.
The horizontal line where a solid object melts and a liquid object freezes is important. On the
horizontal line, energy is being added (melting) or lost (freezing) BUT THE TEMPERATURE
REMAINS THE SAME because the energy is being used to overcome the intermolecular forces.
Heat capacity of an object is the amount of heat energy that it takes to raise the temperature of
the object by one degree.