Brownian motion

 the erratic, jerky movement of tiny particles suspended in a fluid caused by the random impacts of individual molecules in thermal motion.

kinetic energy

the energy of motion.

temperature

a measure of the average kinetic energy of atoms or molecules.

random

scattered equally among all possible choices with no organized pattern.

Fahrenheit scale

a temperature scale with 180 degrees between the freezing and boiling points of water; water freezes at 32°F and boils at 212°F.

Celsius scale

a temperature scale with 100 degrees between the freezing and boiling points of water; water freezes at 0°C and boils at 100°C.

thermometer

an instrument that measures temperature.

thermistor

an electronic sensor that measures temperature by detecting changes

in electrical resistance.

thermocouple

 an electronic sensor made of two different metals that detects a temperature-dependent voltage across them.

absolute zero

 the lowest possible temperature, at which the energy of molecular motion is essentially zero, or as close to zero as allowed by quantum theory.

Kelvin scale

a temperature scale that starts at absolute zero and has the same unit intervals as the Celsius scale: TKelvin = TCelsius + 273.

heat

thermal energy, energy resulting from temperature; the total energy in random molecular motion contained in matter.

joule

the fundamental SI unit of energy (and heat).

calorie

 an older unit of heat

British thermal unit (BTU)

a large unit of heat.

second law of thermodynamics

 law of nature that states that energy (heat) spontaneously flows from higher temperature to lower temperature.

system

 a group of interacting objects and effects that are selected for investigation.

open system

a system which can exchange matter and energy with the surroundings.

closed system

a system which can exchange only energy with the surroundings.

isolated system

 a system in which neither matter nor energy can be exchanged with the surroundings.

first law of thermodynamics

law of nature that states that energy can neither be created nor destroyed, and thus the total energy in an isolated system remains constant; all the energy lost by one system must be gained by the surroundings or another system.

thermal equilibrium

a condition where the temperatures are the same and heat no longer flows from one material to another.

specific heat

the quantity of energy, usually measured in J/(g·°C), it takes per gram of a certain material to raise the temperature by one degree Celsius.

conduction:

the flow of heat energy through the direct contact of matter.

thermal conductor

 a material that conducts heat easily.

thermal insulator

 a material that resists the flow of heat.

phase change

conversion of the organization of molecules in a substance without changing the individual molecules themselves, such as changing from solid to liquid or liquid to gas.

melting point

the temperature at which a substance changes phase from solid to liquid; for example, the melting point of water is 0°C.

heat of vaporization

 the energy required to change the phase of one gram of a material from liquid to gas or gas to liquid at constant temperature and constant pressure at the boiling point.

boiling point

the temperature at which a substance changes phase from liquid to gas

heat of fusion

 the energy required to change the phase of one gram of a material from liquid to solid or solid to liquid at constant temperature and constant pressure at the melting point.

evaporation

a phase change from liquid to gas at a temperature below the boiling point.

condensation

a phase change from gas to liquid; a substance in its gas phase may condense at a temperature below its boiling point.

latent heat

 thermal energy that is absorbed or released by a phase change.

triple point

the temperature and pressure at which the solid, liquid, and gas phases of a substance can all exist in equilibrium together.

relative humidity

the actual partial pressure of water vapor in air divided by the saturation vapor pressure at the same temperature.

dew point

the temperature at which air is saturated with H2O vapor (Rh = 100%).