Thermal Energy, Laws, Phase Changes, and Buoyancy Concepts

Temperature

Measure of the average kinetic energy of a system's molecules

Thermal Energy

Total internal energy of a substance due to particle motion and interactions

Heat

Energy transferred from a hot object to a cold object due to a temperature difference

Thermal Equilibrium

State in which objects in contact have the same temperature and no net heat transfer

Kelvin Scale

Temperature scale that starts at absolute zero (no molecular motion)

Absolute Zero

Lowest possible temperature where particle motion stops (0 K)

Zeroth Law of Thermodynamics

If A and B are each in thermal equilibrium with C, then A and B are in equilibrium with each other

First Law of Thermodynamics

Energy cannot be created or destroyed, only transferred or transformed

Second Law of Thermodynamics

Heat flows naturally from hot to cold, and entropy always increases

Entropy

Measure of disorder or randomness in a system

Specific Heat

Amount of energy required to raise 1 kg of a substance by 1 K (or 1°C)

Heat of Fusion

Energy required to melt 1 kg of a solid at constant temperature

Heat of Vaporization

Energy required to change liquid to gas at constant temperature

Phase Change

Change of matter from one state to another without temperature change

Why temperature stays constant during a phase change

Energy is used to break or form bonds, not increase particle speed

Solid

Particles vibrate in place; definite shape and volume; lowest entropy

Liquid

Particles move past each other; definite volume, no definite shape

Gas

Particles move freely; no definite shape or volume; highest entropy

Conduction

Heat transfer by direct contact between particles (mostly solids)

Convection

Heat transfer by movement of fluids (liquids and gases)

Radiation

Heat transfer by electromagnetic waves; no contact required

Fluid

Substance that can flow and deform under stress (liquids and gases)

Pressure

Force applied per unit area (P=F/A)

Pascal's Principle

Pressure applied to a confined fluid is transmitted equally in all directions

Bernoulli's Principle

As fluid speed increases, pressure decreases

Archimedes' Principle

Buoyant force equals the weight of the displaced fluid

Buoyant Force (floating object)

Equal to the object's weight

Density

Mass per unit volume; determines whether an object floats or sinks

Viscosity

Resistance of a fluid to flow (higher viscosity = thicker fluid)

Buoyancy

The upward force a fluid exerts on an object placed in it

Buoyant Force

The upward force that opposes gravity when an object is in a fluid

Displaced Fluid

The volume of fluid pushed aside by an object placed in it

Floating Condition

An object floats when the buoyant force equals the object's weight

Sinking Condition

An object sinks when its weight is greater than the buoyant force

Density and Floating

Objects less dense than the fluid float; more dense objects sink

Equal Density Condition

If the density of the object equals the density of the fluid, the object is suspended

Buoyant Force on a Floating Object

Equal to the object's weight, not zero

Buoyant Force on a Submerged Object

Equal to the weight of the displaced fluid

Why larger objects can float

They displace more fluid, increasing the buoyant force

Apparent Weight

The reduced weight of an object in a fluid due to buoyant force

What is the process of solid turning into liquid?

Melting

What is the process of liquid turning into solid?

Freezing

What is the process of liquid turning into gas?

Vaporization (evaporation or boiling)

What is the process of gas turning into liquid?

Condensation

What is the process of solid turning directly into gas?

Sublimation

What is the process of gas turning directly into solid?

Deposition