Transcript Chapter 10 Section 2: First Law of Thermodynamics

Chase Chavez, Aaron Blaylock, Josh
Walts, Jim Du, Annie Chen, Jake Kisor
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What are some ways that energy is given off in
a roller coaster?
What do you think thermodynamics is?
How do you think refrigerators work?
What is an example of a cyclic process?
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Chase
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Thermodynamics is a branch of physics
concerned with heat and temperature and their
relation to energy and work. It defines
macroscopic variables, such as internal energy,
entropy, and pressure, that partly describe a
body of matter or radiation.
Jake
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Mechanical energy transfers to the atoms and
molecules of an object
In the case of a rollercoaster most of the energy is
gradually released in the air as heat
“The principle of energy conservation that takes
into account a system’s internal energy as well as
work and heat is called the first law of
thermodynamics”
Jake
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When the systems internal energy increases or
decreases, it could help to visualize the system
as a circle
When work is done or energy is transferred as
heat into the system an arrow points into the
circle
When work or energy is transferred out of the
system the arrow points out of the circle
Chase
Table 1
Signs of Q and W for a System
Q>0
Energy added to system as heat
Q<0
Energy removed from system as heat
Q=0
No transfer of energy as heat
W>0
Work done by system (expansion of
gas)
W<0
Work done on system (compression of
gas)
W=0
No work done
Chase
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A total of 135 J of work is done on a gaseous
refrigerant as it undergoes compression. If the
internal energy of the gas increases by 114 J
during the process, what is the total energy
transferred as heat? Has energy been added to
or removed from the refrigerant as heat.
Page 345—solution
Equation:
U=Q-W
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Cyclic processes is the transfer of energy as heat
and the process of using heat to do mechanical
work.
Unet = 0 and Qnet =Wnet
Heat engines use heat to do work.
A heat engine is similar to a water wheel.
A water wheel uses the energy of falling water
from level to another level above the Earth’s
surface.
This increases the water’s kinetic energy to turn it.
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Josh
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Instead of using potential energy to do work,
heat engines transfer energy from hightemperature substances to low-temperature
substances.
Wnet = Qh – Qc
The larger the difference between the energy
transferred as heat into the engine and out of
the engine means the more work it has done.
Josh
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Page 346
Practice B
Numbers 1 - 5
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https://www.youtube.com/watch?v=_QXH5MaoKEE
&app=desktop
Five Steps of a Gasoline Engine
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Fuel Intake- piston allows fuel in through intake valve. The fuel
mixes with the air
Compression- both valves close and the piston compresses the
mixture
Ignition- the piston makes contact with the spark plug and
causes ignition
Expansion- the product of the combustion and the fuel-air are
relaxed as the piston contract
Exhaust- the second (exhaust) valve opens and the product is
released.
Jim
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https://www.youtube.com/watch?v=NDjfunr2lK
4&app=desktop begin @ :20
Refrigerant-substance that evaporates at a very
low temperature
4 Steps of Refrigeration
The refrigerant continues to absorb energy until energy is
vaporized
 The internal energy and pressure are increased by a
compressor. The compressor does work on the volume
without heat transfer
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Annie
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Refrigerant gives up energy to outside environment.
In a gaseous state, the high pressure condenses it to a
liquid, only if it is at a constant temperature
The liquid refrigerant is then brought back into the
refrigerator. Goes through an expansion valve and
does work as it goes from a high pressure area to a
low pressure area and the volume increases
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The book