Section 2: Concepts of Energy and Entropy

Heat Transfer

Movement of thermal energy from hot to cold.

Thermal Energy

Energy from the motion of particles.

Thermal Equilibrium

State where two objects reach the same temperature.

Conduction

Heat transfer via direct contact; hot particles collide with cool particles. Factors affecting rate include temperature difference, thickness, area, and conductivity.

Thermal Conductivity (k)

How well a material conducts heat; good conductors include metals, while insulators like wood slow heat transfer.

Convection

Heat transfer via fluid movement, including natural (without external forces) and forced (with fans or pumps) convection.

Convection Current

Cycle of rising warm fluid and sinking cool fluid.

Radiation

Heat transfer through electromagnetic waves; includes thermal radiation and emissivity (how efficiently a surface emits thermal radiation).

Thermodynamics

Study of heat and energy transfer; involves systems (part of the universe) and surroundings.

Work and Energy

Work (W) is energy transfer due to force causing motion; energy is the ability to do work.

First Law of Thermodynamics

Energy cannot be created or destroyed; depicted by ΔU=Q−W.

Closed System

Exchanges energy but not matter; includes pressure-volume (P-V) diagrams.

Heat Engine

Converts thermal energy to mechanical work; operates on W=Qh−Qc.

Second Law of Thermodynamics

Heat moves from hot to cold naturally; spontaneous processes cannot revert to original state without energy.

Entropy (S)

Measure of disorder in a system; never decreases in an isolated system, giving time direction.

Efficiency

Ratio of useful work output to heat input; Efficiency=W/Qh.

Energy Transformation

Changing energy from one form to another; includes kinetic energy (KE=1/2mv²) and potential energy (PE=mg*h).

Kinetic Energy (KE)

Energy due to motion; doubling velocity quadruples KE.

Potential Energy (PE)

Stored energy due to position; more height means more gravitational potential energy.

Gravitational Potential Energy

Energy due to height in a gravitational field, described by PE=mg*h.

Elastic Potential Energy

Energy stored in stretched or compressed objects; described by PEs=1/2k*x².

Power

Rate of doing work or transferring energy; Power Formula P=W/t.

Watt (W)

SI unit of power.

Conservative vs Nonconservative Systems

Conservative systems retain energy, while nonconservative forces (e.g., friction) remove it.

Law of Conservation of Energy

Energy changes form; it is not created or destroyed.

Isolated System

No energy enters or leaves.

Pendulum Energy

Max PE at the highest point, max KE at the lowest.

Roller Coaster Energy

PE converts to KE as it goes down.

Work Formula

W=F*d; occurs when force causes displacement.

Positive Work

Adds energy to the system; negative work removes energy.

Zero Work

Occurs when no movement occurs or force is perpendicular to motion.

Living Organisms and Entropy

Maintain order by increasing entropy outside.

Heat Added to a System

Increases internal energy unless work is done.

Work Done by a System

Decreases internal energy.

Heat Pump

Moves heat for heating or cooling.

Refrigerator

Removes heat from its interior.

Efficiency and the Second Law

Not all energy can be converted to work.

Internal Energy (U)

Total energy of particles in a system.

Boundary

Line separating system from surroundings.

Spontaneous Process

Occurs without external energy input.

Irreversible Process

Cannot return to original state without energy.

Reversible Process

Can be reversed without increasing entropy.