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What is AP Physics 2 Thermodynamics?
AP Physics 2 Thermodynamics is the study of heat, energy, and work in physical systems. It includes understanding how energy moves, how gases behave under temperature and pressure, and how heat affects matter.

This guide is designed to answer key questions, simplify complex ideas, At the end of this guide, you’ll get a free downloadable PDF cheat sheet to help you review and revise anytime.

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Table of Contents

1. What is Thermodynamics in AP Physics 2?

2. What are Thermodynamic Systems?

3. The Four Laws of Thermodynamics Explained

4. Understanding the Ideal Gas Law and Thermal Equilibrium

5. Modes of Heat and Energy Transfer

6. Work, Pressure, and Volume in Thermodynamics

7. Thermodynamics and Forces

8. Collisions and Molecular Behavior

9. Entropy, Disorder, and Thermal Equilibrium

10. AP Physics 2 Thermodynamics Formula Cheat Sheet

11. Conclusion and Free Download

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What are Thermodynamic Systems?

A thermodynamic system is a part of the universe chosen for study. Everything outside this system is called the surroundings.

Types of Thermodynamic Systems:

Type	Definition	Real-Life Example
Open System	Exchanges both energy and matter with surroundings	A boiling pot without a lid
Closed System	Exchanges energy but not matter	A sealed gas container
Isolated System	No exchange of energy or matter	A well-insulated thermos

These systems help in analyzing physical changes using the laws of thermodynamics.

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What Are the Laws of Thermodynamics?

There are four laws of thermodynamics, and each plays a role in how heat and energy behave.

Zeroth Law of Thermodynamics

• Definition: If object A is in thermal equilibrium with B, and B with C, then A and C are also in equilibrium.
• Why it matters: This law makes temperature measurement possible.

First Law of Thermodynamics

• Definition: Energy cannot be created or destroyed; it only changes form

Second Law of Thermodynamics

• Definition: In any energy exchange, entropy (disorder) increases.
• Implication: Heat flows from hot to cold, never the other way.

Third Law of Thermodynamics

• Definition: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.

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What Is the Ideal Gas Law and Thermal Equilibrium?

Ideal Gas Law

The Ideal Gas Law connects pressure, volume, temperature, and number of particles in a gas:

$$PV = nRT$$

Use: Helps describe behavior of gases in closed systems like pistons.

What is Thermal Equilibrium?

Two objects are in thermal equilibrium when they are at the same temperature and no heat flows between them. This is important when applying the Zeroth Law and understanding heat transfer.

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How Is Heat Transferred?

Heat moves in three main ways. Understanding this is essential for solving AP Physics 2 problems.

Mode	Description	Example
Conduction	Heat moves through direct contact	Metal spoon in hot tea
Convection	Heat moves through fluid motion	Warm air rising in a room
Radiation	Heat moves through electromagnetic waves	Sun warming your skin

Heat Transfer Formula:

$$Q = mc\Delta T$$

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How Does Work Relate to Pressure and Volume?

In thermodynamic systems, work is done when gas expands or compresses.

Work Formula:

$$W = P\Delta V$$

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Process Types and Work Done:

Process	Constant Variable	Work Done?
Isothermal	Temperature	Yes
Adiabatic	No heat exchange	Yes
Isobaric	Pressure	Yes
Isochoric	Volume	No (ΔV = 0)

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How Do Thermodynamics and Forces Interact?

Force and pressure in a gas result from collisions of molecules against container walls.

• Pressure (P) = Force (F) per area (A):
  $$P = \frac{F}{A}$$ 

This microscopic view helps connect thermodynamics to Newtonian physics.

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What Is the Role of Collisions in Thermodynamics?

In thermodynamic models, particles collide elastically (no energy lost). These collisions:

• Cause gas pressure
• Distribute energy
• Explain temperature as average kinetic energy

The more frequent and energetic the collisions, the higher the temperature and pressure.

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What is Entropy? How Does It Relate to Thermal Equilibrium?

Entropy is a measure of disorder. Systems move naturally toward higher entropy.

Key Points:

• Entropy increases in isolated systems.
• Reaching thermal equilibrium means maximum entropy.
• More microstates = higher entropy.

Example State	Entropy Level
Ice cube (solid)	Low entropy
Steam (gas)	High entropy

This explains why you don’t see heat flow from cold to hot — it would decrease entropy.

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AP Physics 2 Thermodynamics Formula Sheet

Here’s a handy reference table for quick review:

Concept	Formula / Notes
Heat Transfer	$Q = mc\Delta T$
Ideal Gas Law	$PV = nRT$
Work done by gas	$W = P\Delta V$
First Law of Thermodynamics	$\Delta U = Q – W$
Entropy	Always increases in isolated systems
Pressure	$P = \frac{F}{A}$
Efficiency of Engine	$1 – \frac{T_C}{T_H}$
Adiabatic process	$Q = 0$so $\Delta U = -W$
Isochoric process	$W = 0$so $\Delta U = Q$
Thermal Equilibrium	No net heat flow between systems

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Get your free AP Physics 2 Thermodynamics Review PDF here

AP Physics 2 Thermodynamics Review PDF

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Thermodynamics can seem abstract, but once you understand the flow of energy and how systems respond, it starts to click. This guide provides not just a cheat sheet but a structured way to master the concepts for your AP Physics 2 exam.

✅ Use this page for quick reviews
✅ Bookmark it before your next test
✅ Practice problems to reinforce the ideas