Engines: Crash Course Physics #24
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Date: 2022-04-04
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Comments and reviews: 10
Jay
Thanks! The production value is great. However:
At 05: 00 you say that there is an isothermal process where heat is slowly added, but the animation shows lots of heat (Q_H) escaping. What gives?
At 05: 04 You say that the isothermal expansion is 1/2 AB. Shouldn't it be the -entire- path AB?
At 05: 15 you say -the temperature drops whilst the heat stays constant, which also makes the volume expand-. Well this is misleading: a temperature drop would cause an isolated system volume to contract. However in a Carnot engine, the system is doing work on the atmosphere, converting internal energy into work, and dropping the temperature. It's best to say that the expansion work drops the temperature, not that a colder temperature causes an expansion.
Also, when you keep saying -the heat stays constant-, shouldn't you be saying -there is no heat flow- or something equivalent?
At 05: 40 you say -the heat doesn't change- but perhaps you should be saying that there is no heat flow, or the system is thermally insulated, or something else equivalent.
The way you explain it sounds as if heat is a state property, when it's not.
reply
Thanks! The production value is great. However:
At 05: 00 you say that there is an isothermal process where heat is slowly added, but the animation shows lots of heat (Q_H) escaping. What gives?
At 05: 04 You say that the isothermal expansion is 1/2 AB. Shouldn't it be the -entire- path AB?
At 05: 15 you say -the temperature drops whilst the heat stays constant, which also makes the volume expand-. Well this is misleading: a temperature drop would cause an isolated system volume to contract. However in a Carnot engine, the system is doing work on the atmosphere, converting internal energy into work, and dropping the temperature. It's best to say that the expansion work drops the temperature, not that a colder temperature causes an expansion.
Also, when you keep saying -the heat stays constant-, shouldn't you be saying -there is no heat flow- or something equivalent?
At 05: 40 you say -the heat doesn't change- but perhaps you should be saying that there is no heat flow, or the system is thermally insulated, or something else equivalent.
The way you explain it sounds as if heat is a state property, when it's not.
reply
Joshua
The animation of a refrigerator at work is completely reversed and incorrect: after the liquid is turned into a gas it is compressed at which point it flows to the condenser to shed the heat extracted in the fridge(and the heat generated by being compressed) and return to a liquid. This liquid is then sent through an orifice or long, thin capillary tube so that it pressure is reduced hence it's temperature lowered. This liquid then goes to the evaporator inside the fridge where it absorbs heat from the interior and boils into a gas before returning to the compressor. The animation shows the compressor as a -decompressor- or expansion device(orifice, capillary tube) and that is opposite of it's true function as the whole thing is reversed.
reply
The animation of a refrigerator at work is completely reversed and incorrect: after the liquid is turned into a gas it is compressed at which point it flows to the condenser to shed the heat extracted in the fridge(and the heat generated by being compressed) and return to a liquid. This liquid is then sent through an orifice or long, thin capillary tube so that it pressure is reduced hence it's temperature lowered. This liquid then goes to the evaporator inside the fridge where it absorbs heat from the interior and boils into a gas before returning to the compressor. The animation shows the compressor as a -decompressor- or expansion device(orifice, capillary tube) and that is opposite of it's true function as the whole thing is reversed.
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LaughingInfidel
These videos are good overall, but that's just an awful description of how a refrigerator works. She doesn't even mention the pressure difference in the two halves of the loop.
Also, all you young'uns with working high-pitch hearing need to learn how to use the equalizer on your computer or phone.
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These videos are good overall, but that's just an awful description of how a refrigerator works. She doesn't even mention the pressure difference in the two halves of the loop.
Also, all you young'uns with working high-pitch hearing need to learn how to use the equalizer on your computer or phone.
reply
education
she fitted all engineering and technological/industrial applications of thermodynamics of the last episode in less than 10 minutes. too much information for a small amount of time = she spoke fast. as if she; s on a hurry. . now I knew that steam engines and refrigerators are machine cousins. :)
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she fitted all engineering and technological/industrial applications of thermodynamics of the last episode in less than 10 minutes. too much information for a small amount of time = she spoke fast. as if she; s on a hurry. . now I knew that steam engines and refrigerators are machine cousins. :)
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Gibillan
before my summer vacation they were exactly sincronised with what i did at school. in the vacation they we don't do, so it's perfectly sincronized now too: ) helps me a lot, as this year we have a bad teacher
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before my summer vacation they were exactly sincronised with what i did at school. in the vacation they we don't do, so it's perfectly sincronized now too: ) helps me a lot, as this year we have a bad teacher
reply
Ethan
I spent an hour this morning reading about thermodynamic engines from a Physics textbook and still had trouble understanding. Then I watch this 10 minute video and immediately understand what's going on.
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I spent an hour this morning reading about thermodynamic engines from a Physics textbook and still had trouble understanding. Then I watch this 10 minute video and immediately understand what's going on.
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gofres
A nice recap for those that understand the principles already but far too quick for new comers. Was hoping to use this in a lesson on the Otto cycle but it's above and beyond my year 13 pupils!
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A nice recap for those that understand the principles already but far too quick for new comers. Was hoping to use this in a lesson on the Otto cycle but it's above and beyond my year 13 pupils!
reply
Ren-
Compilation Guy>>>> And I need a crash course on basic gymnastics and acrobatics that covers front- and backhandspring, front and back somersault, aerial, side-somersault and handstand.
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Compilation Guy>>>> And I need a crash course on basic gymnastics and acrobatics that covers front- and backhandspring, front and back somersault, aerial, side-somersault and handstand.
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Adam
Is there a quantity to describe how well a real engine compares to a Carnot engine working across the same temperature range. Like actual efficiency/Carnot efficiency
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Is there a quantity to describe how well a real engine compares to a Carnot engine working across the same temperature range. Like actual efficiency/Carnot efficiency
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Matthew
pro tip to watching these fast videos: pause between sentences to mimic a realistic conversation and time for your brain to understand what she just said.
reply
pro tip to watching these fast videos: pause between sentences to mimic a realistic conversation and time for your brain to understand what she just said.
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