
English: 
Think of all the developments throughout history that lead to the conveniences you enjoy today
If I had to pick the biggest game changer in human technology, it would probably be the steam engine
During the industrial revolution, the steam engine powered machines in farms and factories
And although it may not seem so, those advances eventually lead to the technologies that you're using to watch me right now
So the steam engine was a pretty big deal
Developing a practical steam engine involved a lot of time and a lot of smart people and about 100 years and three main inventors
And it took a solid understanding of thermodynamic processes and heat engines to make this world changing technology a reality
Heat engines, like steam engines turn thermal energy into mechanical work
And they do it in a repeating cycle

Arabic: 
فكّر بكل التطورات على مدى التاريخ التي
أدت إلى الرفاهيات التي تتمتع بها اليوم.
إن أردت أن أسمي أكثر اختراع غيّر حياتنا في
تاريخ البشرية، فسأقول أنه المحرك البخاري.
أثناء الثورة الصناعية، أمدّ المحرك البخاري
الآلات في المزارع والمصانع بالطاقة.
وبالرغم من أنك قد تستغرب هذا ولكن هذه
التطورات أدت إلى التقنيات التي تشاهدني بها
إذاً، كان المحرك البخاري أمراً مهماً.
إنشاء محركٍ بخاريٍ عمليٍ تطلب الكثير من
الوقت والعديد من الناس الأذكياء، وقرن
تقريباً وثلاثة مخترعين رئيسيين. وتطلب
فهماً دقيقاً للعمليات التيرموديناميكية
- والمحركات الحرارية - لإنجاز هذا
الإختراع المغيّر للعالم، حقيقةً واقعةً.
المحركات الحرارية، كالمحركات البخارية،
تحول الطاقة الحرارية إلى عمل مكانيكي،
ويفعلون ذلك في حلقة ذاتية التكرار.

English: 
Think of all of the developments throughout history that led to the conveniences you enjoy today.
If I had to pick the biggest game-changer in human technology, it would probably be the steam engine.
During the industrial revolution, the steam
engine powered machines in farms and factories.
And, although it may not seem so, those advances eventually led to the technologies that you’re using to watch me, right now.
So, the steam engine was a pretty big deal.
Developing a practical steam engine involved a lot of time and a lot smart people, and about a hundred years, and three main inventors.
And it took a solid understanding of thermodynamic processes – and heat engines – to make this world-changing technology, a reality.
[Theme Music]
Heat engines, like steam engines, turn thermal energy into mechanical work, and they do it in a repeating cycle.

Arabic: 
تبدأ العملية في درجة حرارة عمل عليا،
ونرمز لها T_H،
 وتنتهي بدرجة حرارة عمل دنيا،
نرمز لها T_L.
في العملية، يأخذ المحرك الحرارة المضافة
التي استخدمت لرفع درجة الحرارة،
ويرمز لها Q_H، ويحول بعضها إلى عمل، بينما
يطلق بعض الحرارة - Q_L - كحرارة مستنفذة.
ثم ترتفع درجة حرارة المحرك مرة
أخرى، فيبدأ بالدورة مجدداً.
حسناً، عُد بتفكيرك إلى القانون الأول من
ديناميكية الحرارة،
والذي ينص على أن التغيّر في طاقة نظام
الحرارية يساوي العمل والحرارة.
في حالة المحرك الحراري، التغيّر في الطاقة
الحرارية صفر، لأنه يعود دائماً إلى درجة
حرارة البداية. إذاً، حرارة المحرك المضافة
يجب أن تساوي العمل الذي يؤديه زائد الحرارة
التي يطلقها، والآن لنرى كيف سيحصل
هذا في محرك بخاري.
توجد عدة أنواع مختلفة من المحركات البخارية
ولكننا سنركز على النوع الترددي البسيط.
طالما أن لديك شيئاً ما "لتسخين" البخار،
مثل الفحم أو النفط، سيستمر المحرك بالعمل.
هذه هي الحركة المضافة.
تستخدم الحركة المضافة لتسخين حجم معين من
الماء، والذي يتحوّل إلى بخار.
ثم، يفتح صمام إدخال، ليسمح بدخول
البخار إلى المحرك.
يتمدد البخار ويدفع مكبساً إلى الخارج،
وهذه هو العمل الذي يؤديه المحرك.

English: 
The process starts at a high operating temperature, which we label as T_H, and ends up at a lower operating temperature, T_L.
In the process, the engine takes the input
heat that was used to raise the temperature,
known as Q_H, and turns some of it into work, while also releasing some heat – Q_L – as exhaust.
Then the engine’s temperature is raised once more, so it can start the cycle all over again.
OK, now think back to the first law of thermodynamics, which says that the change in the thermal energy of a system is equal to heat and work.
In the case of a heat engine, the change in thermal energy is zero, because it always returns to the temperature it started from.
So, the engine’s input heat must be equal
to the work it does, plus the heat it releases.
Now let’s see how this plays out in a steam
engine.
There are a few different types of steam engine, but we’ll focus on the basic reciprocating type.
As long as you have something to "heat" the steam, like coal or oil, the engine keeps working.
That’s the input heat.
The input heat is used to heat a volume of
water, which turns to steam.
Then, an intake valve opens, allowing the
steam into the engine.
The steam expands and moves a piston outward
– that’s the work done by the engine.

English: 
The process starts at a high operating temperature which we label 'TH' and ends up at a lower operating temperature: 'TL'
In the process, the engine takes the input heat which was used to raise the temperature known as 'QH' and turns some of it into work...
while also releasing some heat 'QL' as exhaust
Then the engine's temperature is raised once more so it can start the cycle all over again
OK, now think back to the first law of thermodynamics,
Which says that the change in thermal energy of a system is equal to heat and work
In the case of a heat engine,
The change in thermal energy is zero because it always returns to the temperature is started from
So the engine's input heat must be equal to the work it does plus the heat it releases
Now let's see how this works out in a steam engine
There are a few different types of steam engine
but all focus from the basic reciprocating type
as long as you have something to heat the steam like coal or oil, the engine keeps working
That's the input heat
The input heat is used to heat a volume of water which turns to steam
then an intake valve opens, allowing steam into the engine
The steam expands and moves a piston outward

Arabic: 
ثم يغلق صمام الإدخال، ويفتح
صمام العادم.
يؤدي صمام العادم إلى مكثّف، والذي
يبرّد البخار ويرجعه ماءً.
درجة الحرارة الدنيا تخفض الضعط، مما يخلق
فراغاً جزئياً يجعل المكبس يعود إلى مكانه.
ثم يعاد تسخين الماء وتحويلها إلى بخار،
وتبدأ الدورة مجدداً.
عندما يعمل المحرك، يمكن تحويل حركة المكبس
إلى كل انواع الحركات المختلفة.
وهذا هو سبب قدرة المحرك البخاري على تحريك
القطارات والقوارب وتسيير خطوط المعامل.
ولكن عندما يعمل المحرك،
يقوم بإطلاق حرارة مستنفذة.
كلما زادت كمية الحرارة المستنفذة التي
يطلقها، كلما قلّت فعالية المحرك،
وكلما ازدادت كمية الطاقة التي عليك
أن تعطيه إياها ليؤدي العمل ذاته.
وبالطبع من المهم أن تكون المحركات
فعالّة قدر ما أمكن لتوفير الطاقة.
ولتصميم محرك فعال، على المهندسين أن
يكونوا قادرين على حساب فعاليته.
مثلما قلنا قبلاً، حرارة المحرك المضافة
مساوية للعمل الذي يؤديه+الحرارة المستنفذة.
وكلما ازداد العمل - وقلّت الحرارة
المستنفذة - الذي تجنيه من الحرارة المضافة
كلما ازدادت فعالية المحرك. إذاً، الفعالية
تساوي العمل الذي يؤديه المحرك على الحرارة

English: 
That's the work done by the engine, then an intake valve closes and an exhaust valve opens
The exhaust valve leads to a condenser which cools the steam back into water
The lower temperature also lowers the pressure, creating a partial vacuum that makes the piston move back into its original position
Then the water gets heated back into steam and the cycle starts over
As the engine runs, the motion of the piston can be translated into all kinds of different movement
Which is how steam engines can do things like move trains and boats and run factory lines
But, as the steam engine runs, it releases exhaust heat
Obviously, it's important for engines to be as efficient as possible to save energy
And to design an efficient engine, engineers have to be able to calculate its efficiency
Like we said earlier, an engine's input heat is equal to the work it does plus its exhaust heat
And the more work and therefore the less exhaust heat you get out of the input heat,
the more efficient your engine is
So efficiency is equal to the work done by an engine divided by its input heat

English: 
Then the intake valve closes, and an exhaust
valve opens.
The exhaust valve leads to a condenser, which
cools the steam back into water.
The lower temperature also lowers the pressure, creating a partial vacuum that makes the piston move back into its original position.
Then the water gets heated back into steam,
and the cycle starts over.
As the engine runs, the motion of the piston can be translated into all kinds of different movement,
which is how steam engines can do things like
move trains and boats, and run factory lines.
But as the steam engine runs, it releases
exhaust heat.
The more exhaust heat it produces, the less efficient the engine is, and the more energy you have to put in for the same amount of work.
Obviously, it’s important for engines to
be as efficient as possible to save energy.
And to design an efficient engine, engineers
have to be able to calculate its efficiency.
Like we said earlier, an engine’s input heat is equal to the work it does, plus its exhaust heat.
And the more work – and therefore, the less exhaust heat – you get out of the input heat, the more efficient your engine is.
So, efficiency is equal to the work done by
an engine divided by its input heat.

Arabic: 
المضافة. نستطيع أيضاً أن نعبر عن ذلك
باستخدام  الحرارة والحرارة المستنفذة
- بسهولة بالغة - . نعلم أن العمل يساوي
الحرارة المضافة ناقص الحرارة المستنفذة.
إذاً الفعالية تساوي الحرارة المضافة ناقص 
الحرارة المستنفذة، على الحرارة المضافة.
أو لتبسيط تلك المصطلحات: الفعالية هي
1-الحرارة المستنفذة/الحراة المضافة.
وإن لم يطلق محركك أي حرارة مستنفذة
على الإطلاق؟
نقول عندئذٍ أن فعاليته 1 تماماً.
وسيكون فعالاً تماماً.
ولكن لا وجود للمحرك الذي لا يطلق
أي حرارة مستنفذة.
لن يعمل، لأنه يحتاج لأن تنخفض درجة الحرارة
وترتفع مجدداً لكي يعمل المحرك.
ولكننا نستطيع أن نتخيل محركاً مثالياً، حيث
لاتكون الحرارة المستنفذة حرارة ضائعة - حيث
لا يوجد احتكاك أو غيره -. المحرك المثالي
قابل للعكس، أي أنك تستطيع أن تشّغله
بشكل عكسي، فيؤدي عملاً لنقل الحرارة من شيء
ذو درجة حرارة أقل إلى شيء ذو درجة حرارة
أعلى. يسمى هذا المحرك الإفتراضي محرك
كارنوت، ونستطيع استخدامه
لإكتشاف أعلى فعالية ممكنة لمحرك واقعي.
في المرة الماضية، تكلمنا عن أربع أنواع
رئيسية للعمليات الترموديناميكية البسيطة.

English: 
we can also put this just in terms of input heat and exhaust heat, pretty easily, actually
We know that work is equal to input heat minus exhaust heat so efficiency is equal to:
input heat minus exhaust heat divided by the input heat.
Or simplifying those terms: efficiency is equal to 1 minus exhaust heat over input heat.
If your engine produced no exhaust heat at all,
we'd say that its efficiency is exactly one
It would be perfectly efficient
But there is no such thing as an engine that produces no exhaust heat at all
It wouldn't work, because the temperature needs to be losered and then raised again for the engine to keep going.
But we can imagine an ideal engine where none of the exhaust energy is waste heat
Where there's no friction or anything like that
An ideal engine would also be reversible—meaning, you could run it backward, putting in work to transfer heat
from something with a lower temperature to something with a higher temperature.
This type of hypothetical engine is called a carnot engine
And we can use it to figure out the maximum possible efficiency of a real life engine
Last time we talked about the four types of basic thermodynamic processes

English: 
We can also put this just in terms of input
heat and exhaust heat – pretty easily, actually.
We know that work is equal to input heat minus
exhaust heat.
So efficiency is equal to input heat minus
exhaust heat, divided by the input heat.
Or, simplifying those terms: efficiency is
equal to 1 - exhaust heat / input heat.
If your engine produced no exhaust heat at all?
We’d say that its efficiency was exactly 1.
It would be perfectly efficient.
But there’s no such thing as an engine that
produces no exhaust heat at all.
It wouldn’t work, because the temperature needs to be lowered and then raised again for the engine to keep going.
But we can imagine an ideal engine, where none of the exhaust energy is waste heat – where there’s no friction or anything like that.
An ideal engine would also be reversible – meaning, you could run it backward, putting in work to transfer heat from something with a lower temperature to something with a higher temperature.
This kind of hypothetical engine is called a Carnot engine, and we can use it to figure out the maximum possible efficiency of a real-life engine.
Last time, we talked about the four types
of basic thermodynamic processes.

English: 
The Carnot Engine combines two of those types into whats known as the Carnot cycle
But in the Carnot cycle, those processes don't transfer heat between areas with different temperatures
Because if an engine involves heat transfer from an area with a higher temperature to an area with a lower temperature,
then reversing the engine would involve transferring heat from lower to higher
which would violate the 2nd law of thermodynamics
So in the Carnot cycle,heat won't flow between areas with different temperatures at all
instead, the cycle goes through two adiabatic processes where heat is held constant
and two isothermal processes where heat is transferred
But the temperature is held constant so the heat never flows between areas of different temperatures
Now, you might be wondering how the heat gets transferred if there's no difference in temperature,
well, remember how we described the isothermal processes last time
In those cases, there are only very tiny differences in temperature
and they're immediately eliminated
so, practically speaking, there is no transfer of heat between areas of different temperatures and this means the process can still be reversed
with all that in mind, here's how a Carnot engine really works, at least in theory

English: 
The Carnot engine combines two of those types
into what’s known as the Carnot cycle.
But in the Carnot cycle, those processes don’t transfer heat between areas with different temperatures.
Because, if an engine involves heat transfer from an area with a higher temperature to an area with a lower temperature, then reversing the engine would involve transferring heat from lower to higher.
Which would violate the second law of thermodynamics!
So, in the Carnot cycle, heat won’t flow between areas of different temperatures at all.
Instead, the cycle goes through two adiabatic processes, where heat is held constant, and two isothermal processes, where heat is transferred.
But the temperature is held constant, so the heat never flows between areas of different temperatures.
Now, you might be wondering how heat gets transferred, if there’s no difference in temperature.
Well, remember how we described isothermal
processes last time:
In those cases, there are only very tiny differences in temperature, and they’re immediately eliminated.
So, practically speaking, there is no transfer
of heat between areas of different temperatures.
And this means, the process can still be reversed.

Arabic: 
محرك كارنوت يدمج نوعان منها في ما يعرف
بإسم دورة كارنوت.
ولكن في دورة كارنوت، هذه العمليات لا تنقل
الحرارة بين مناطق مختلفة بدرجة الحرارة.
لأن إن تضمن المحرك على نقل حرارة من منطقة
ذات درجة حرارة أعلى إلى منطقة ذات درجة
حرارة أخفض، فعكس المحرك سيتضمن نقل حرارة
من ذات الدرجة الدنيا إلى ذات الدرجة العليا
وهذا خرق للقانون الثاني من ديناميكية
الحرارة.
إذاً، في دورة كارنوت، الحرارة لا تتدفق بين
المناطق ذات درجة الحرارة المختلفة أبداً.
بل تمرّ الدورة بعمليتين ثابتتي الحرارة،
حيث تيقى الحرارة ثابتة،
وعمليتين عازلتين لدرجة الحرارة،
حيث تنتقل الحرارة. ولكن
تبقى درجة الحرارة ثابتة، إذاً فلا تتدفق
الحرارة بين مناطق مختلفة بدرجة الحرارة.
والآن، قد تتسائلون عن كيف يمكن للحرارة أن
تنتقل دون تتغير درجة الحرارة.
حسناً، تذكروا كيف وصفنا العمليات عازلة
درجة الحرارة في المرة الماضية:
في هذه الحالات، توجد اختلافات ضئيلة بدرجة
الحرارة، ولكن يتم التخلص منها فوراً.
إذاً، عملياً، لا يحدث نقل حرارة بين مناطق
ذات درجة حرارة مختلفة.
هذا يعني، أن العملية قابلة للإنعكاس.
بأخذ ذلك بعين الإعتبار، هذه هي طريقة عمل
محرك كارنوت،

English: 
because again, Carnot engines are totally hypothetical
The first process in the cycle is isothermal
The temperature is constant but heat is slowly added
that makes the gas's volume expand and its pressure decrease
path A-B on this diagram
the second process is adiabatic: the temperature drops while the heat stays constant
which also makes the volume expand and the pressure decrease
that's path B-C on the diagram
the third process it the opposite of the first one, and it's also isothermal
the gas is compressed whilst the temperature is held constant
so it releases heat and its pressure increases while its volume decreases
that's path C-D
The last process is the opposite of the second
it's adiabatic, so the gases compress but its heat doesn't change
that makes the gas's volume decrease and its pressure increase
like in path D-A
Its temperate goes back up to the starting point
the Carnot engine is the ideal engine
because it produces the most possible work from a given temperature difference

Arabic: 
نظرياً على الأقل بما أن محركات كارنوت
خيالية تماماً.
أول عملية في الدورة هي عملية عازلة
لدرجة الحرارة.
درجة الحرارة ثابتة، ولكن الحرارة
تضاف ببطء.
يجعل هذا حجم الغاز يتمدد وضغطه ينخفض
- المسار a-b على الرسم البياني -
العملية الثانية هي عملية ثابتة الحرارة.
تنخفض درجة الحرارة بينما تبقى الحرارة
ثابتة، مما يجعل الحجم يتمدد والضغط ينخفض.
ذلك هو المسار a-b  على الرسم البياني.
العملية الثالثة هي عكس الأولى،
وهي عملية عازلة لدرجة الحرارة أيضاً.
يضعط الغاز بينما تبقى درجة الحرارة 
ثابتة،
لذا يطلق حرارة ويزداد ضغطه بينما ينخفض
حجمه.
وذلك هو المسار c-d.
العملية الأخيرة هي عكس الثانية: إنها ثابتة
الحرارة إذاً الغاز ينضغط ولكن حرارته ثابتة
هذا يجعل حجم الغاز يقلّ وضغطه يزداد،
مثل المسار d-a.
تعود درجة حرارته إلى نقطة البداية.
محرك كارنوت هو المحرك المثالي، لأنه ينتج
أكثر عمل ممكن من فرق درجة حرارة معين.
ولأن محرك كارنوت يحقق أكبر فعالية ممكنة،

English: 
With all that in mind, here’s how a Carnot engine works – at least in theory, because again: Carnot engines are totally hypothetical.
The first process in the cycle is isothermal.
The temperature is constant, but heat is slowly
added.
That makes the gas’s volume expand and its
pressure decrease – path a-b on this diagram.
The second process is adiabatic.
The temperature drops while the heat stays constant, which also makes the volume expand and the pressure decrease.
That’s path b-c on the diagram.
The third process is the opposite of the first
one, and it’s also isothermal.
The gas is compressed while the temperature is held constant, so it releases heat and its pressure increases while its volume decreases.
That’s path c-d.
The last process is the opposite of the second: it’s adiabatic, so the gas is compressed but its heat doesn’t change.
That makes the gas’s volume decrease and
its pressure increase, like in path d-a.
Its temperature goes back up to the starting
point.
The Carnot engine is the ideal engine, because it produces the most possible work from a given temperature difference.

Arabic: 
تتناسب درجات الحرارة العليا والدنيا
مع الحرارة المضافة والمستنفذة،
وذلك مهم حسابياً، لأن هذا يعني
أن في معادلة الفعالية،
تستطيع أن تستبدل Q_H و Q_L
- الحرارة المضافة والحرارة المستنفذة -
بـ T_H و T_L  - درجتا حرارة العمل
العالية والمنخفضة - .
مما قد يكون مفيداً إن كنت لا تعلم حرارة
المحرك المضافة والمستنفذة، ولكنك تعلم درجتا
حرارة عمله. إذاُ! الفعالية المثالية لمحرك
تساوي: 1-حرارته الدنيا/ حرارته العليا.
كلما كانت درجة حرارة عمله الدنيا أقلّ،
كلما ازدادت فعالية نسخة المحرك المثالية.
إذاً، لنقل أنك تحتاج لمحرك ليشغّل سيارة
ماريو بالحجم الواقعي تبنيها لنفسك.
تجد محركاً على الإنترنت، وتفكر بشرائه ولكن
أولاً عليك اكتشاف مدى فعاليته.
موقع المصنع يقول أنه في كل ثانية، حرارة
المحرك المضافة هي 10 كيلوجول إلى 700 كيلفن.
وحرارته المستنفذة هي 2 كيلوجول
إلى300 كيلفن.
معادلة الفعالية تقول أن فعالية المحرك
تساوي:
1-حرارته المستنفذة/حرارته المضافة،
في هذه الحالة 0.8.
سيكون ذلك محركاً فعالاً جداً،
لذا يجب أن تشكّ بالأمر قليلاً.
أعني، هل هذه الفعالية ممكنة حتى؟

English: 
and because the Carnot engine is as efficient as possible, the high and low temperatures are proportional to its input and exhaust heat
which is important math-wise because it means that in the equation for efficiency, you can replace QH and QL, the input and exhaust heat
with TH and TL the higher and lower operating temperatures
which can help if you don't know an engine's input and exhaust heat
but you do know its operating temperatures
So the ideal efficiency for an engine is equal to 1 minus its low temperature divided by its high temperature
The colder that lower operating temperature is, the more efficient the ideal version of the engine is
So, say you need an engine to power a life-sized mario kart
you find an engine online and you're thinking about buying it, but first you want to know how efficient it is
the manufacturer's website says that for every second the engine's input heat is 10kJ at 500K
its exhaust heat is 2kJ @ 300K"
The efficiency equation states that the engine's efficiency is equal to 1 minus this exhaust heat divided by its input heat
In this case, 0.8. That would be a very efficient engine
so you should be a little bit suspicious
is that knid of efficiency even possible?

English: 
And because a Carnot engine is as efficient as possible, the high and low temperatures are proportional to the input and exhaust heat.
Which is important, math-wise, because it
means that in the equation for efficiency,
you can replace Q_H and Q_L – the input and exhaust heat – with T_H and T_L – the higher and lower operating temperatures.
Which can help if you don’t know an engine’s input and exhaust heats, but you know its operating temperatures.
So! The ideal efficiency for an engine is equal
to: 1 - its low temperature / its high temperature.
The colder that lower operating temperature is, the more efficient the ideal version of the engine is.
So, say you need an engine to power a life-size
Mario Kart that you’re building for yourself.
You find an engine online, and you’re thinking about buying it, but first you want to know how efficient it is.
The manufacturer’s website says that for every second, the engine’s input heat is 10 kilojoules at 500 Kelvin.
Its exhaust heat is 2 kilojoules at 300 Kelvin.
The efficiency equation says that the engine’s efficiency is equal to: 1 - its exhaust heat / its input heat – in this case, 0.8.
That would be a very efficient engine, so
you should be a little suspicious.
I mean, is that kind of efficiency even possible?

Arabic: 
تستطيع الإكتشاف، بفحص فعالية المحرك
المثالية أي فعالية كارنوت.
الفعالية المثالية تساوي : 1-درجة حرارة
عمله الدنيا/درجة حرارة عمله العليا
وفي هذه الحالة،
ذلك يساوي 0.4.
من المستحيل لهذا المحرك أن تزيد فعاليته
عن 0.4، إذاً موقع المصنع... يكذب.
إذاً يجب عليك ألا تشتري منهم شيئاً.
وفي الواقع أنت لا ترغب بمحرك فعاليته قريبة
من فعالية محرك كارنوت، لأن محركات كارنوت
بطيئة جداً. خلال هذه العمليات العازلة لدرجة
الحرارة، على درجة الحرارة أن تبقى ثابتة
بينما تنتقل الحرارة، وذلك ينجح
فقط إذا انتقلت الحرارة ببطء شديد.
إذاً على المحرك أن يكون بطيئاً جداً.
إن كان لديك محرك كارنوت في سيارتك، مثلاً،
سيستغرقك الخروج من مدخلك يوماً كاملاً.
المحركات الحرارية الواقعية مفيدة، لأنها
تستخدم تدفق الحرارة من شيء دافئ لآخر بارد
لأداء عمل. ولكن ماذا لو كنت تريد أن تتدفق
الحرارة من شيء بارد لشيء أدفأ؟
هذا ما تفعله مكيفات الهواء والثلّاجات،
وقد اخترعت هذه الأشياء أساساً
باستخدام المبادئ التي تعلمها العلماء
من صنع المحركات البخارية.

English: 
you can find out by checking the ideal efficiency of the engine: the Carnot efficiency
the ideal efficiency is equal to one minus its lower operating temperature, divided by its higher operating temperature, which in this case is equal to 0.4
It's impossible for this engine to have an efficiency higher than 0.4, so the manufacturer's website is... well, just lying.
So you probably shouldn't buy anything from them anyway.
And actually, you probably wouldn't want an engine that was close to the efficiency of a Carnot engine
because Carnot engines are very slow
During those isothermal processes, the temperature has to be kept constant while heat is transferred—which only works if the heat is transferred super slowly.
So the engine has to be really slow.
If you had a Carnot engine in your car for example, it would take you a whole day to get out of your driveway
Real life heat engines are useful because they use the flow of heat from something warmer to something cooler to produce work
But what if you want heat to flow from something cooler to something warmer?
That's what things like air conditioners and refrigerators do, and they were originally developed using the principles
scientists had learned from creating steam engines.

English: 
You can find out, by checking the ideal efficiency
of the engine – the Carnot efficiency.
The ideal efficiency is equal to: 1 - its lower operating temperature / its higher operating temperature, which in this case is equal to 0.4.
It’s impossible for this engine to have an efficiency higher than 0.4, so the manufacturer’s website is...well, just lying.
So you probably shouldn’t buy anything from them anyway.
And, actually, you probably wouldn’t want an engine that was close to the efficiency of a Carnot engine, because Carnot engines are very slow.
During those isothermal processes, the temperature
has to be kept constant while heat is transferred
– which only works if the heat is transferred
super slowly.
So the engine has to be really slow.
If you had a Carnot engine in your car, for example, it would take you a whole day to get out of your driveway.
Real-life heat engines are useful, because they use the flow of heat from something warmer to something cooler to produce work.
But what if you want heat to flow from something
cooler to something warmer?
That’s what things like air conditioners and refrigerators do, and they were originally developed using the principles scientists had learned from creating steam engines.

English: 
These cooling machines are a lot like the opposite of heat engines, in the sense that they use work to make heat flow in the opposite direction that it would normally go.
The refrigerator, for example, passes a cool
liquid through the inside of the fridge.
The liquid absorbs heat – that’s Q_L – as
it evaporates.
Then, the fridge uses a motor to do work on the now-warmer fluid, which has turned into a gas.
It’s passed through coils on the outside of the refrigerator, where it releases the exhaust heat – Q_H – and cools to become a liquid again.
Then the cycle starts over.
For heat engines, efficiency is measured by the work produced for a given amount of input heat.
And there’s a similar concept for refrigerators: the coefficient of performance, or COP, which is equal to the amount of heat removed from the lower-temperature zone divided by work.
The more heat the fridge removes for a given amount of work, the higher the coefficient of performance.
Like we did with the efficiency equation, we can rewrite the COP equation just in terms of Q_L and Q_H.
The coefficient of performance is equal to
Q_L divided by Q_H minus Q_L.

English: 
These cooling machines are a lot like the opposite of heat engines in the sense that they use work to make heat flow in the opposite direction that it would normally go
The refrigerator for example passes a cool liquid through the inside of a fridge
The liquid absorbs heat (that's 'QL') as it evaporates
then the fridge uses the motor to do work on the now warmer fluid which is turned into a gas
It's passed through coils on the outside of the refrigerator where it releases the exhaust heat: 'QH'
and cools to become a liquid again
then the cycle starts over
for heat engines, efficiency is measured by the work produced for a given amount of input heat
and there's a similar concept for refrigerators
The coefficient of performance, or COP, which is equal to the amount of heat removed from the lower temperature zone divided by the work.
The more heat the fridge removes for a given amount of work, the higher the coefficient of performance
like we did with the efficiency equation, we can re-write the COP equation just in terms of QL and QH
the coefficient of performance is equal to QL divided by QH minus QL
to find the coefficient for performance for an ideal refrigerator,

Arabic: 
آلات التبريد هذه تشبه المحركات الحرارية
المعكوسة، أي أنها
تستخدم العمل لجعل الحرارة تتدفق في الإتجاه
المعاكس لإتجاهها الطبيعي.
الثلاجة، مثلاً، تمرر سائلاً بارداً
في داخلها.
يمتص السائل الحرارة - وهي Q_L -
وهو يتبخر.
ثم، تستخدم الثلاجة محركاً ليؤدي عملاً
على السائل الذي أصبح أدفأ، وتحوّل إلى غاز.
يمرّ في أنابيب ملتفة خارج الثلاجة، حيث
يطلق حرارة -Q_H - ويبرد ليتحول لغاز مجدداً
ثم تكرر الدورة نفسها.
في المحركات الحرارية، تقاس الفعالية بالعمل
المنتج لقاء كمية معينة من الحرارة المضافة.
وهناك فكرة مشابهة في الثلاجات:
معامل الأداء أو COP،
والذي يساوي كمية الحرارة المزالة من منطقة
درجة الحرارة الدنيا تقسيم العمل.
كلما ازدادت الحرارة التي تزيلها الثلاجة
عند أداء عمل معين، كلما ازداد معامل الأداء.
مثلما فعلنا بمعادلة الفعالية، نستطيع إعادة
صياغة معادلة COP  بمصطلحات Q_L و Q_H فقط.
COP=Q_L/Q_H - Q_L
لإيجاد معامل الأداء لثلاجة مثالية،
نفعل نفس الشيء الذي فعلناه

English: 
To find the coefficient of performance for an ideal refrigerator, we do the same thing we did with the ideal Carnot engine: replace Q_L with T_L and Q_H with T_H.
So, for an ideal fridge, the coefficient of performance would be equal to: the lower operating temperature, divided by the higher operating temperature minus the lower operating temperature.
And of course, a real-life refrigerator can’t have a higher coefficient of performance than an ideal refrigerator.
Now, it may not be surprising that steam engines
and refrigerators are total opposites.
But! Fridges and freezers and air conditioning are all game-changing inventions that were only made possible by our knowledge of steam engines.
Today, you learned about how engines turn thermal energy into work and how to calculate their efficiency.
We also described the Carnot engine.
And finally, we talked about cooling machines,
like refrigerators.
Crash Course Physics is produced in association
with PBS Digital Studios.
You can head over to their channel and check out a playlist of the latest episodes from shows like:
PBS Space Time, Deep Look, and Blank on Blank.
This episode of Crash Course was filmed in
the Doctor Cheryl C. Kinney Crash Course Studio

Arabic: 
مع محرك كارنوت المثالي: نستبدل Q_L بـ T_L
و Q_H بـ T_H.
إذاً، لثلاجة مثالية، معامل الأداء يساوي:
درجة حرارة العمل الدنيا
تقسيم درجة حرارة العمل العليا ناقص
درجة حرارة العمل الدنيا.
وبالطبع، لا يمكن لثلاجة واقعية أن تمتلك
معامل أداء أعلى من ثلاجة مثالية.
والآن، قد لا تتفاجئ بأن المحركات البخارية
والثلاجات طرفي نقيض.
ولكن! الثلاجات والبرادات ومكيفات الهواء
اختراعات ثورية
ممكنة فقط بسبب معرفتنا بالمحركات البخارية
اليوم، تعلمتم كيف تحول المحركات الطاقة
الحرارية إلى عمل وكيف نحسب فعاليتهم.
وصفنا أيضاً محرك كارنوت.
وأخيراً، تكلمنا عن آلات التبريد
مثل الثلاجات.
ينتج Crash Course Physics بالتعاون مع
PBS Digital Studios.
تستطيعون التوجه إلى قناتهم ومشاهدة
قائمة بأحدث الحلقات من برامج مثل:
PBS Space Time, Deep Look,
و Blank on Blank.
صورت هذه الحلقة من Crash Course في استديو 
Doctor Cheryl C. Kinney Crash Course Studio

English: 
we do the same thing that we did for he ideal Carnot engine
replace QL with TL and QH with TH
So, for an ideal fridge, the coefficient of performance would be equal to the lower operating temperature divided by the higher operating temperature minus the lower operating temperature.
and of course a real life refrigerator can't have a higher coefficient of performance than an ideal refrigerator
now it may not be surprising that steam engines and refrigerators are total opposites
but fridges and freezers and air conditioning are all game changing inventions that were only made possible by our knowledge of steam engines!
Today you learned about how engines turn thermal energy into work and how to calculate their efficiency.
Crash Course Physics is produced in association with PBS Digital Studios. You can head over to their channel and check out
a playlist of the latest episodes from shows like PBS Space Time, Deep Look, and Blank on Blank.
This episode of Crash Course was filmed in the Doctor Cheryl C. Kinney Crash Course Studio with the help of these amazing people

Arabic: 
بمساعدة هؤلاء الأشخاص الرائعين
وفريق رسومياتنا الرائع هو Thought Cafe.

English: 
with the help of these amazing people and our equally amazing graphics team, is Thought Cafe.

English: 
and our equally amazing graphics team is Thought Café.
