Physics — Thermal Science

The Science of Heat, Work & Energy

Thermodynamics governs everything from the engine in your car to the CPU in your laptop. Master the four laws, explore real applications, and test your knowledge.

Begin Learning → Take the Quiz
4
Fundamental Laws · from Zeroth to Third
5
Thermodynamic Processes · Isothermal, Adiabatic & more
∞
Real-world applications · engines, CPUs, refrigerators
Q = Heat added to system W = Work done by system ΔU = Change in internal energy S = Entropy T = Temperature (Kelvin) η = Efficiency P = Pressure · V = Volume
Module 01
The Four Laws of Thermodynamics
These four laws define how energy behaves in the universe — from temperature measurement to the arrow of time itself.
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Zeroth Law

Thermal Equilibrium
Foundation
A 90°C C Reference B 90°C =T =T ∴ A and B are also in equilibrium
If two systems are each in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. This law defines temperature as a measurable property.
Mathematical Statement
If T_A = T_C and T_B = T_C  →  T_A = T_B
Real-world examples & deeper context
Example 1

A thermometer works because of the Zeroth Law. When you put a thermometer in contact with your body, they reach thermal equilibrium — and the thermometer reading equals your body temperature.

Example 2

Two rooms connected through a wall will eventually reach the same temperature — thermal equilibrium with the surrounding environment.

Why "Zeroth"?

It was named after the First and Second laws were already established, yet it is more fundamental. Scientists added it retroactively as "Zeroth" to preserve the existing numbering.

⚡

First Law

Conservation of Energy
Core Law
System ΔU Heat (Q) +In Work (W) Out Radiation
Energy cannot be created or destroyed — it only changes form. The change in a system's internal energy equals the heat added minus the work done by the system.
Mathematical Statement
ΔU = Q − W
Real-world examples & deeper context
Combustion Engine

Burning fuel (Q in) drives a piston (W out). The engine converts chemical potential energy → thermal → mechanical. Some ΔU heats the engine block.

Human Body

Food calories (Q in) power your muscles (W out) and keep your body warm (ΔU). You can't get more work out than the energy stored in food.

Key Insight

A perpetual motion machine of the first kind — producing work without any energy input — is physically impossible under this law.

🌊

Second Law

Entropy Always Increases
Direction of Time
HOT T_H = 600K COLD T_C = 300K Natural Flow → Reverse requires work
The total entropy of an isolated system always increases or stays constant. Heat flows spontaneously from hot to cold — never the reverse without external work input.
Clausius Inequality
ΔS_total ≥ 0  for any real process
Real-world examples & deeper context
Refrigerator

A fridge moves heat from cold (inside) to hot (room) — but only by consuming electrical work. It doesn't violate the Second Law; it uses external energy to drive heat "uphill".

Arrow of Time

The Second Law explains why time has a direction. A broken egg never reassembles; dissolved sugar never spontaneously crystallises — because the disordered states have vastly higher entropy.

Heat Engine Limit

No heat engine can be 100% efficient. Some energy is always lost to entropy increase in the cold reservoir — this is why the Carnot limit exists.

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Third Law

Absolute Zero
Limit
0K ∞ Ordered (S→0) Disordered
As a system's temperature approaches absolute zero (0 K / −273.15 °C), its entropy approaches a minimum constant value. A perfect crystal at 0 K has exactly zero entropy.
Nernst Statement
S → 0  as  T → 0 K
Real-world examples & deeper context
Superconductors

Near absolute zero, certain materials exhibit superconductivity — zero electrical resistance — a direct consequence of quantum states becoming ordered.

Why Can't We Reach 0 K?

The Third Law implies that it would take an infinite number of steps to cool a system to exactly absolute zero. It is an asymptotic limit — you get ever closer but never arrive.

Coldest Place

NASA's Cold Atom Lab aboard the ISS has cooled atoms to 100 pico-Kelvin (0.0000000001 K) — a billionth of a degree above absolute zero.

Module 02
Thermodynamic Processes
Each process holds a different variable constant, leading to fundamentally different behaviour of a gas system.
Isothermal
Constant: T
Temperature held fixed. Heat absorbed equals work done. Follows PV = const. Examples: slow compression in a water bath.
Adiabatic
Constant: Q = 0
No heat exchange with surroundings. Work changes internal energy only. Air rising rapidly in atmosphere cools adiabatically.
Isobaric
Constant: P
Pressure held fixed. Most common in everyday life — boiling water at atmospheric pressure is isobaric.
Isochoric
Constant: V
Volume is fixed; no work done (W = 0). All heat goes into internal energy. Pressure cooker explosions occur at isochoric-like conditions.
Polytropic
PV^n = const
Generalised process encompassing all the above (n = 0 isobaric, n = 1 isothermal, n = γ adiabatic, n = ∞ isochoric).

P–V Diagram: All Four Processes

V P Isothermal Adiabatic Isobaric Isochoric Initial state
Module 03
The Carnot Cycle
The most efficient heat engine theoretically possible. Invented by Sadi Carnot in 1824, it sets the absolute upper limit on engine efficiency.
V P 1 2 3 4 Isothermal (T_H) Adiabatic Isothermal (T_C) Adiabatic W_net (shaded area)
1→2
Isothermal Expansion
Gas expands at constant temperature T_H. Heat Q_H is absorbed from the hot reservoir. Work is done by the gas.
2→3
Adiabatic Expansion
Gas expands with no heat exchange. Temperature drops from T_H to T_C. Work is still done by the gas.
3→4
Isothermal Compression
Gas is compressed at constant temperature T_C. Heat Q_C is rejected to the cold reservoir.
4→1
Adiabatic Compression
Gas is compressed with no heat exchange. Temperature rises back to T_H, completing the cycle.
Carnot Efficiency
η = 1 − (T_C / T_H)
50.0%
Maximum possible efficiency between these temperatures
Module 04
Entropy Particle Visualizer
Watch disorder increase in real-time. Entropy is not chaos — it's the statistical tendency towards more probable states.

Live Particle System

Particles confined to a partition. Release the barrier to watch entropy increase.

Order
100%
Entropy S
0.00
Temperature
298 K
298K
Module 05 — Applied
CPU Thermal Management
Thermodynamics in your PC. Control the CPU, thermal paste and fan to see the Second Law in action.
HEATSINK AIR GAP CPU IDLE MOTHERBOARD MAX MIN
30°C
CPU Temp
28°C
Heatsink
—
Status
System idle — CPU at ambient temperature (30 °C).
System Log
[00:00]System initialised. Ambient: 30°C.
THERMAL RESISTANCE PATH
CPU → Air Gap ≈ 30 °C/W → Heatsink → Still Air → Ambient
Module 06 — Tools
Formula Calculator
Solve common thermodynamics problems. Select a formula, enter your known values, and get the result instantly.

Thermodynamic Calculator

Result appears here

Common Constants

Universal Gas Constant (R) 8.314 J/(mol·K)
Boltzmann Constant (k_B) 1.38 × 10⁻²³ J/K
Absolute Zero 0 K = −273.15 °C
Water specific heat (c) 4186 J/(kg·K)
Stefan-Boltzmann (σ) 5.67 × 10⁻⁸ W/(m²·K⁴)
Avogadro Number (Nₐ) 6.022 × 10²³ mol⁻¹
Module 07 — Test
Knowledge Quiz
10 questions covering all four laws, processes, and real applications. See how well you've mastered thermodynamics.

Thermodynamics Assessment

Select the best answer for each question

0/10
Quiz Complete
Module 08 — Reference
Glossary of Terms
A quick-reference dictionary of essential thermodynamic concepts, symbols, and definitions.