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Energy notes
ENERGY IS THE ABILITY OF A PHYSICAL SYSTEM
TO DO WORK
1. LAWS OF CONSERVATION OF
MATTER/MASS…….. and ENERGY!!!!!!!
 The law of conservation of mass states that
the mass of an isolated system (closed to all
matter and energy) will remain constant over
time
 The law of conservation of energy states that the
total amount of energy in an isolated
system remains constant over time. The total
energy is said to be conserved over time.
THE FIRST LAW OF THERMODYNAMICS
STATES THAT IN A CLOSED SYSTEM, THE TOTAL
AMOUNT OF ENERGY MUST REMAIN THE SAME.
THAT MEANS THAT ENERGY CAN NEITHER
BE CREATED NOR DESTROYED: IT CAN
HOWEVER BE TRANSFORMED FROM ONE FORM
TO ANOTHER.
The energy into a system =
the energy that comes out of the system
THE SECOND LAW OF THERMODYNAMICS
(COMES IN THREE FORMS)
FORM 1:
IN ANY TRANSFORMATION OF ENERGY FROM
ONE FORM TO ANOTHER, THERE IS ALWAYS A
DECREASE IN THE AMOUNT OF USEFUL
ENERGY
FORM 2:
HEAT CANNOT, BY ITSELF, FLOW FROM COLD
TO HOT.
IT SPONTANEOUSLY FLOWS FROM
HOT TO COLD.
FORM 3:
IN ANY CLOSED SYSTEM, DISORDER HAS A
NATURAL TENDENCY TO INCREASE. Entropy
increases if no energy is allowed to enter a
system
Entropy = disorder
WHAT IS A SYSTEM?
A system is an arrangement of parts which interact with
each other within the system's boundaries to function as a
whole. The nature (purpose) of the whole is always
different from, and more than, the sum of its unassembled
collection of parts.
A system is a group of parts that does a specific job.
CLOSED AND OPEN SYSTEMS:
CLOSED SYSTEM—A SYSTEM WHERE
NOTHING ENTERS OR LEAVES; WHERE
EVERYTHING IS USED AND REUSED
e.g. (Earth is a closed system with regard to
matter)
OPEN SYSTEM—A SYSTEM WHERE THINGS
BOTH ENTER AND LEAVE
e.g. (Earth is an open system with regard to
energy)
STEADY STATE— A SYSTEM IN WHICH
PROPERTIES ARE CONSTANT BECAUSE
SUBSTANCES ARE ENTERING AND LEAVING
AT THE SAME RATE
STATIC—showing little or no change:
DYNAMIC—changing:
THE SIX FORMS OF ENERGY:
1. MECHANICAL ENERGY—ENERGY OF
MOTION OR POTENTIAL FOR MOTION
2. HEAT (THERMAL) ENERGY—FORM OF
KINETIC ENERGY THAT FLOWS FROM ONE
BODY TO ANOTHER BECAUSE OF A
TEMPERATURE DIFFERENCE BETWEEN THEM.
The effects of heat energy result from the motion of
molecules.
Heat energy is the kinetic energy of moving molecules
Can be transferred in three ways:
1. conduction: is the transfer of energy
through solid matter from particle to
particle. Heat is conducted through a
solid material much the same way
electricity is. Conduction is slowed
by insulation
2. convection: Convection is the
transfer of heat energy through a gas
or liquid by movement of currents.
Heat is carried by the fluid
3. radiation: is electromagnetic waves
which directly transport heat energy
through space. Sunlight is radiated
through space to our planet without
the aid of fluids or solids
3. RADIANT ENERGY (INCLUDING LIGHT)
This energy is demonstrated by the electromagnetic
spectrum
4. ELECTRICAL ENERGY—the energy of electric
charges. Never used as an end product in itself. It is
used to make things do work, because it is easily
converted into other forms of energy.
5. CHEMICAL ENERGY—energy stored in the
bonds that hold molecules together. Common
examples of chemical energy include:
 Foods
 Dried plant material (firewood!!!)
 Fossil fuels (gasoline, diesel,
crude oil, coal)
This energy is initially trapped by plants
during photosynthesis!
6. NUCLEAR ENERGY—energy locked in the
nuclei of atoms. When the particles that make
up atomic nuclei are rearranged, energy is
released
WORK CAN ONLY BE DONE WHEN THERE IS A
DIFFERENCE IN THE ENERGY CONTENT OF
OBJECTS.
TYPES OF ENERGY TRANSFER
CONDUCTION-the transfer of thermal energy from
molecule to molecule HEAT ENERGY FROM SOLID
TO SOLID
CONVECTION-the transfer of heat by the mass
movement of heated particles as in air or liquid
currents HEAT ENERGY THROUGH AIR
RADIATION-that energy which is sent out from an
object, like the sun or a light bulb-can be particles or
waves
In any energy conversion (from one form of energy
to another,) some useful energy is lost to the
environment as heat energy. This decreases the
efficiency of the transformation.
Energy EfficiencyThe efficiency of a machine equals the amount of
energy that comes out of a machine divided by the
energy that goes into a machine ALL multiplied by
100% (the multiplication factor exists because
efficiency is expressed as a percent.)
IE: efficiency = (useful energy out/ useful
energy in) x 100%
The efficiency of a system requires analyzing the
efficiency of each step.
If a system has three steps, and each step is 75%
efficient, then the whole system’s efficiency can be
expressed thus:
(75%) x (75%) x (75%) =
(.75) x (.75) x (.75) = 0.422 = 42%