Thermodynamics Lab
Explore the fundamental rules of Energy, Entropy, and Engines.
Zeroth Law
"If A = B and B = C, then A = C (in temperature)."
First Law
"Energy cannot be created or destroyed."
ΔU = Q - W. Energy doesn't vanish; it just changes from heat to work.Second Law
"Entropy (disorder) always increases."
Third Law
"Entropy approaches zero at 0 Kelvin."
You Can't Win, You Can't Break Even.
A famous joke summarizes Thermodynamics:
1. You can't win (Conservation of Energy).
2. You can't break even (Entropy).
3. You can't quit the game (Absolute Zero).
Entropy is "Time"
Most physics equations work forwards and backwards. Gravity works the same if you play the video in reverse. Thermodynamics does not.
You can turn an egg into an omelet, but you can never turn an omelet back into an egg. The Second Law gives the universe a "direction" (Time's Arrow).
Why 100% is Impossible
To turn heat into work, heat must flow from a hot place to a cold place.
If the Cold Sink (Tc) warms up to match the Hot Source (Th), the flow stops. The engine dies. You ALWAYS need a cold sink to dump waste heat into.
η = 1 - Tc / Th
Why car engines only get ~30% efficiency.
Frequently Asked Questions
What are the 4 Laws of Thermodynamics?
Zeroth Law: Defines temperature. First Law: Energy is conserved (cannot be created/destroyed). Second Law: Entropy always increases (time flows forward). Third Law: Absolute Zero cannot be reached.
What is Entropy?
Entropy ($S$) is often described as 'disorder', but more accurately it is a measure of the number of possible microscopic configurations a system can have. A smashed egg has higher entropy than a whole egg. The universe constantly moves towards higher entropy.
Is Perpetual Motion possible?
No. A 'perpetual motion machine' violates either the First Law (creating energy from nothing) or the Second Law (operating at 100% efficiency without waste heat). It is physically impossible.
What determines the efficiency of an engine?
The efficiency depends only on the temperature difference between the heat source and the cold sink. The greater the difference, the higher the max specific efficiency. This is the Carnot Limit.
Why does heat flow from hot to cold?
Because it is statistically overwhelmingly more probable. Fast-moving particles (hot) collide with slow-moving particles (cold) and transfer energy. The reverse (randomly bunching all fast particles together) is so unlikely it never happens.
Who was Maxwell's Demon?
A thought experiment by James Clerk Maxwell. He imagined a tiny demon who opens a door to let only fast molecules through, separating hot from cold without doing work (decreasing entropy). It was later proven that the act of 'measuring' or 'remembering' the molecule's speed generates enough entropy to save the Second Law.
What is the 'Heat Death' of the universe?
If entropy always increases, eventually all energy in the universe will be evenly spread out. There will be no hot or cold spots, meaning no work can be done. The universe will be a cold, dark, uniform soup.
Why can't we reach Absolute Zero?
The Third Law states that it takes an infinite number of steps to cool something to exactly 0 K. We can get to 0.000000001 K, but never exactly zero.
What is the First Law formula?
$\Delta U = Q - W$. The change in Internal Energy ($U$) equals Heat added ($Q$) minus Work done by the system ($W$).
Are living things violations of Entropy?
No. Life creates order (low entropy) locally, but only by creating a massive amount of disorder (heat/waste) in the surroundings. The total entropy of the universe still increases.