Temperature and Heat

Temperature

a measure of hotness or coldness, influencing the direction of heat flow.

Heat

the energy in transit caused by temperature differences.

Kelvin Scale

defines absolute temperature, where 0 K represents a state with no thermal energy

Thermodynamics

• the study of energy transformations involving heat, mechanical work, and other aspects of energy and how these transformations relate to the properties of matter.

• Applications: car engines, refrigerators, biochemical processes, and the structure of stars.

Thermal Physics

A broader term of thermodynamics which includes statistical mechanics (microscopic particle models).

Zeroth Law of Thermodynamics

• states that if two systems are in thermal equilibrium with a third system, then they are in equilibrium with each other.

• Two systems are in thermal equilibrium if and only if they have the same temperature.

Temperature

• Everyday experience tells us that objects come to a common “warmth” or “coldness” after contact. This everyday sensation hints at a measurable physical parameter — temperature.

• Scientifically, the concept of temperature arises from the idea of thermal equilibrium. And it can be understood from both macroscopic and microscopic perspectives.

Macroscopic, Macroscopically

• viewpoint that looks at matter from the outside, focusing on quantities we can measure directly, such as pressure, volume, and temperature.

• __________, temperature is what a thermometer reads and tells us how hot or cold something is.

Microscopic, Microscopically

• viewpoint that looks inside matter, focusing on how individual particles (atoms or molecules) move and interact.

• ___________, temperature represents the average kinetic energy of the molecules in a material, that is how fast its particles are moving. The faster the particles move, the higher the temperature.

Celsius and Fahrenheit

units that define fixed points

Kelvin

provides an absolute scale with absolute zero being the theoretical lowest temperature.

Celsius

Daily temperature, general science

Fahrenheit

U.S. weather, some engineering fields

Kelvin

Physics, thermodynamics, scientific research

Thermometers

make use of some physical property that changes with temperature and can be calibrated to make the temperature measurable.

Pressure

measured by the gauge, increases or decreases as the gas becomes hotter or colder.

Thermal Expansion

• refers to the change in dimensions of solids, liquids, and gases with temperature.

• At the atomic level, as temperature increases, the average energy of these particles increases, altering the equilibrium spacing between them.

• This phenomenon is universal across all phases of matter.

Heat

is energy transferred between systems only because they have a temperature difference ΔT. Iftwo bodies are in thermal equilibrium, their temperatures are equal and Q = 0

Energy

what heat morphs into as it is transferred

Specific Heat

When heat flows into a substance, part of the energy raises molecular kinetic energy, causing temperature to change. For a mass m undergoing a temperature change ΔT

Heat transfer

occurs through three distinct physical mechanisms: conduction, convection and radiation

Conduction

occurs within a body or between two bodies in contact. It is heat transfer through collisions and vibrations. It is dominant in solids, particularly metals.

Heat current

rate of heat flow

Insulators

Materials with low thermal conductivity

Thermal Conductivity

depends on the material of the object

Convection

depends on motion of mass from one region of space to another. It involves heat transfer by the motion of fluid (liquid or gas)

Forced Convection

If the fluid is circulated by a blower or pump

Natural Convection or Free Convection

if the flow is caused by differences in density due to thermal expansion, such as hot air rising,

Radiation

is the heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies. All objects emit electromagnetic radiation due to thermal motion of charged particles.

Global Warming

refers to the increase in the Earth’s average surface temperature overtime, largely due to human activities that increase greenhouse gases (such as CO₂) in the atmosphere.