Undergraduate
  1. Classical mechanics  1.1. dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. projectile motion  1.1.4. Relative speed  1.1.5. Uniform circular motion  1.1.6. Non-uniform circular motion  1.1.7. Reference frames and transformations  1.2. Newton's Laws of Motion  1.2.1. First law of motion  1.2.2. Second law of motion  1.2.3. Third Law of Motion  1.2.4. Applications of Newton's Laws  1.2.5. Friction and its types  1.2.6. Free Body Diagram  1.2.7. Constraints and pseudo-forces  1.3. Work and Energy  1.3.1. work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy in classical mechanics  1.3.5. Conservative and non-conservative forces  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.4. Speed and collisions  1.4.1. Linear momentum  1.4.2. Conservation of momentum  1.4.3. Impulse and impact force  1.4.4. Elastic and inelastic collision  1.4.5. Center of mass and speed  1.4.6. Rocket Propulsion  1.5. Rotational motion  1.5.1. Torque and Angular Momentum  1.5.2. Moment of inertia  1.5.3. Rotational Kinematics  1.5.4. Rotational Energy  1.5.5. Rolling Motion  1.5.6. Precession and gyroscopic motion  1.6. Gravitational force  1.6.1. Newton's law of universal gravitation  1.6.2. Gravitational potential energy  1.6.3. Orbital mechanics  1.6.4. Kepler's laws of planetary motion  1.6.5. Gravitational field and potential  1.7. Fluid mechanics  1.7.1. Pressure and Pascal's Principle  1.7.2. Buoyancy and Archimedes' principle  1.7.3. Fluid Dynamics and Bernoulli's Principle  1.7.4. Viscosity and Poiseuille's law  1.7.5. Surface tension and capillarity  1.8. Oscillations and waves  1.8.1. Simple Harmonic Motion  1.8.2. Damped and driven oscillations  1.8.3. Coupled oscillations and common modes  1.8.4. Wave properties and types  1.8.5. Sound Waves and the Doppler Effect  1.8.6. Wave interference and superposition
  2. Electromagnetism  2.1. Electrostatics  2.1.1. Electric charge and properties  2.1.2. Coulomb's law  2.1.3. Electric field and electric potential  2.1.4. Gauss's Law  2.1.5. Capacitance and Dielectric  2.1.6. Electric dipole and potential energy  2.2. Electric circuits  2.2.1. Current and Resistance  2.2.2. Ohm's law  2.2.3. Kirchhoff's Laws  2.2.4. RC Circuit  2.2.5. AC Circuits and Reactance  2.2.6. Electric power and energy  2.3. Magnetism  2.3.1. Magnetic Fields and Forces  2.3.2. Ampere's Law  2.3.3. Magnetic dipole moment  2.3.4. Biot-Savart law  2.3.5. Magnetic Materials and Hysteresis  2.4. Electromagnetic induction  2.4.1. Faraday's Law  2.4.2. Lenz's law  2.4.3. Self and mutual induction  2.4.4. Transformers and Inductive Circuits  2.5. Maxwell's equations  2.5.1. Gauss's law for electricity  2.5.2. Gauss's law for magnetism  2.5.3. Faraday's law of induction  2.5.4. Ampere-Maxwell law  2.5.5. Electromagnetic waves
  3. Thermodynamics  3.1. Laws of Thermodynamics  3.1.1. Zeroth law of thermodynamics  3.1.2. First law of thermodynamics  3.1.3. Second Law  3.1.4. Third Law  3.2. Heat and work  3.2.1. Heat transfer (conduction, convection, radiation)  3.2.2. Thermal expansion  3.2.3. Heat engines and refrigerators  3.2.4. Carnot cycle and efficiency  3.3. Statistical mechanics  3.3.1. Maxwell–Boltzmann distribution  3.3.2. Entropy and Probability  3.3.3. Partition function  3.3.4. Fermi–Dirac and Bose–Einstein statistics
  4. Optics  4.1. Geometrical Optics  4.1.1. Reflection and Refraction  4.1.2. Mirrors and lenses  4.1.3. Optical Instruments  4.1.4. Fermat's principle  4.2. Wave optics  4.2.1. Interference in wave optics  4.2.2. Diffraction  4.2.3. Polarization  4.2.4. Coherence and holography
  5. Quantum mechanics  5.1. Wave–particle duality  5.1.1. Blackbody radiation in wave–particle duality in quantum mechanics  5.1.2. Photoelectric effect  5.1.3. Compton scattering  5.1.4. De Broglie wavelength  5.2. Schrödinger Equation  5.2.1. Time-independent Schrödinger equation  5.2.2. Particle in a box  5.2.3. Quantum Tunneling  5.2.4. Potential wells and obstacles  5.3. Quantum States  5.3.1. Wave function  5.3.2. Quantum operators  5.3.3. Heisenberg uncertainty principle  5.3.4. Angular momentum and spin
  6. Relativity  6.1. Special relativity  6.1.1. Lorentz transformations  6.1.2. Time expansion and length contraction  6.1.3. Relativistic energy and momentum  6.2. General relativity  6.2.1. Principle of Equivalence  6.2.2. Schwarzschild metric  6.2.3. Gravitational waves  6.2.4. Black holes and event horizons
  7. Solid state physics  7.1. Crystal structure  7.1.1. Bravais lattices  7.1.2. X-ray diffraction  7.1.3. Band theory  7.1.4. Phonons and lattice vibrations  7.2. Electrical and Magnetic Properties  7.2.1. Conductors, Semiconductors and Insulators  7.2.2. Superconductivity  7.2.3. Hall effect
  8. Nuclear and particle physics  8.1. Atomic Structure  8.1.1. Atomic Model  8.1.2. Nuclear binding energy  8.2. Radioactivity  8.2.1. Alpha, beta, gamma decay  8.2.2. Half life  8.2.3. Nuclear Fission and Fusion  8.3. Particle physics  8.3.1. Standard Model  8.3.2. Quarks and Leptons  8.3.3. antimatter  8.3.4. Fundamental interactions
  9. Astrophysics and cosmology  9.1. Stellar evolution  9.1.1. Star formation  9.1.2. Black holes and neutron stars  9.1.3. White dwarfs and supernovae  9.2. Cosmology  9.2.1. The Big Bang Theory  9.2.2. Dark matter and dark energy  9.2.3. Cosmic microwave background

Undergraduate → Thermodynamics ↓


Heat and work


Understanding the concepts of heat and work is fundamental to thermodynamics and important for a variety of applications in physics and engineering. These concepts help us describe how energy is transferred within a system and between systems.

Introduction to thermodynamics

Thermodynamics is the study of energy transfer and transformations. It is primarily concerned with the three main types of energy transfer: heat, work, and the internal energy of systems. Heat and work are the two primary forms in which energy is transferred across the boundaries of a system.

Key definitions

  • System: The part of the universe we are focusing on. This could be as small as the gas inside a piston or as large as the Earth.
  • Environment: Everything outside the system that can interact with it.
  • Boundary: A real or imaginary line that separates a system from its surroundings.
  • State of a system: The state of a system, described by its properties, such as temperature, pressure, and volume.
  • Heat (Q): Energy transferred from one system to another without mechanical work. It flows due to temperature differences.
  • Work (W): Energy transferred when a force is applied over a distance or when a displacement occurs within the boundary of a system.

Heat

Heat is a form of energy transfer that is driven by temperature differences between systems or system components. If there is a temperature gradient, heat will naturally flow from the hotter medium to the colder medium until thermal equilibrium is reached.

Example of heat transfer

Consider a cup of hot coffee placed on a table. Over time, the coffee cools down. This cooling occurs because the heat energy from the coffee is transferred to the surrounding cooler air. In this scenario, the coffee is the system, and the air around it is the surroundings.

Mathematical representation of heat

Q = m * c * ΔT

Where:

  • Q is the heat transferred.
  • m is the mass of the substance.
  • c is the specific heat capacity of the substance.
  • ΔT is the change in temperature.

Visual example

Heat flow Cold Warm

The diagram above shows heat flow from a hot object to a cold object. The energy arrows indicate the direction of heat transfer.

Work

In thermodynamics, work is energy that is transferred over a distance by applying a force. For example, when you push a piston in a cylinder, you are doing mechanical work on the system by transferring energy to it.

Example of work

Imagine a gas in a cylinder with a moving piston attached to it. As the gas is heated, it expands and pushes the piston outward, doing work on the surroundings.

Mathematical formulation of work

W = P * ΔV

Where:

  • W is the work done by the system.
  • P is the pressure.
  • ΔV is the change in volume.

Visual example

Work done

This diagram shows a piston being pushed by an expanding gas, and visually demonstrates how the motion of the piston performs work.

Difference between heat and work

While both heat and work are forms of energy transfer, they are fundamentally different in terms of how they are transferred and how they affect a system. Heat flows due to temperature differences, while work involves force and motion. Furthermore, processes that involve heat transfer may not always produce work, and vice versa.

Text example

Consider baking a cake in an oven. The heat from the oven is transferred to the cake batter, cooking the cake. While energy is transferred (heat), no additional work is done on the cake batter. Compare this to a steam engine, where the steam does work on the pistons to drive the engine.

First law of thermodynamics

The first law of thermodynamics, also called the law of conservation of energy, relates changes in internal energy to the heat added to the system and the work done by the system. It is represented mathematically as:

ΔU = Q - W

Where:

  • ΔU is the change in the internal energy of the system.
  • Q is the heat added to the system.
  • W is the work done by the system.

This law ensures that energy is conserved in a closed system. It also highlights that both heat and work can change the internal energy of a system.

Applications and examples

Heat and work are fundamental concepts that apply to a variety of real-world scenarios, from engines and refrigerators to biological systems.

Engine

Engines are a classic example of work produced from heat. In an internal combustion engine, heat is produced by burning fuel, which expands gases that do work on the engine's pistons. This mechanical work is what powers vehicles.

Refrigerator

Refrigerators work on the principle of extracting heat from a cold space and releasing it to a warm space, which requires work input. This process involves a cycle of refrigerant compression and expansion.

Biological systems

Our bodies are biological systems that also manage heat and work. The food we eat provides energy that our bodies convert into work (metabolism, physical activity) and heat.

Text example

Imagine you are using an air conditioner in the summer. The air conditioner transfers heat from inside the room to the outside, thereby cooling the room. This process involves work done by the air conditioner's compressor which moves the refrigerant around its internal cycle.

Conclusion

Heat and work are two important components of thermodynamics, which provide the framework for understanding and manipulating energy transfer. By applying these principles, we can solve practical problems in various fields, optimize energy use, and develop new technologies.


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Heat and work

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