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transfer is a crucial concept in physics, involving the movement of thermal energy between objects. It occurs through , , and , each with unique characteristics and applications in everyday life and technology.

Understanding heat transfer is essential for grasping , which explores the relationship between heat, energy, and work. This knowledge helps explain various phenomena, from phase changes to thermal expansion, and has practical applications in engineering and everyday life.

Heat and Energy Transfer

Energy transfer through heat

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  • Heat transfers thermal energy from a hotter object to a colder object
    • Thermal energy flows from high temperature to low temperature until is reached where both objects have the same temperature
  • Heat transfer occurs through three main mechanisms
    • Conduction transfers thermal energy through direct contact between particles in solids, liquids, and gases at a rate depending on the material's (metals)
    • Convection transfers thermal energy through the movement of fluids as heated fluid expands, becomes less dense, and rises, while cooler fluid sinks, creating a convection current (boiling water)
    • Radiation transfers thermal energy through electromagnetic waves without requiring a medium and can occur in a vacuum with emission and absorption depending on the object's temperature and surface properties (sunlight)
      • The describes the total energy radiated per unit surface area of a black body across all wavelengths per unit time

Conversions between heat and work

  • The relates the amount of work done to the amount of heat generated as demonstrated by showing a specific amount of work always produces the same amount of heat
  • The relationship between heat and work is given by Q=WQ = W where QQ is the heat generated and WW is the work done, both measured in joules
  • The cc of a substance relates the amount of heat required to change its temperature using the equation Q=mcΔTQ = mc\Delta T where
    1. QQ is the heat transferred in joules
    2. mm is the mass of the substance in kilograms
    3. cc is the specific in joules per kilogram per kelvin
    4. ΔT\Delta T is the change in temperature in kelvins

Effects of heat on substances

  • is the sum of the kinetic and potential energies of the particles within a substance which can change by heat transfer altering the kinetic and potential energies of its particles
  • When heat is added to a substance, its particles gain kinetic energy, resulting in an increase in temperature with the amount of change depending on the substance's specific heat capacity (water vs. metal)
  • Phase changes occur when a substance absorbs or releases heat without a change in temperature
    • Melting changes a solid to a liquid and requires heat input known as the (ice melting)
    • Vaporization changes a liquid to a gas and requires heat input known as the (boiling water)
    • Condensation changes a gas to a liquid and releases heat (steam condensing)
    • Freezing changes a liquid to a solid and releases heat (water freezing)
  • The energy required for phase changes depends on the substance's
    • is the energy required to change a substance from solid to liquid or released during freezing (ice)
    • is the energy required to change a substance from liquid to gas or released during condensation (steam)
  • Thermodynamics is the study of heat, temperature, and their relation to energy and work
  • is a measure of the disorder or randomness in a system, which tends to increase in natural processes
  • Heat capacity is the amount of heat required to raise the temperature of an object by one degree, related to but distinct from specific heat capacity
  • Thermal expansion is the tendency of matter to change its shape, area, and volume in response to a change in temperature

Key Terms to Review (24)

Change in entropy: Change in entropy is the measure of the disorder or randomness in a system as it undergoes a process. It quantifies the energy dispersal and unavailability for doing work.
Conduction: Conduction is the transfer of heat through a material without the involvement of any bulk motion of the material. It occurs when heat flows from a region of higher temperature to a region of lower temperature within a material or between materials in direct contact, without any displacement of the material itself.
Convection: Convection is a mode of heat transfer that involves the movement of a fluid, such as air or water, to transport thermal energy from one location to another. It occurs when the temperature difference between a surface and the surrounding fluid causes the fluid to circulate, transferring heat in the process.
Entropy: Entropy is a measure of the disorder or randomness in a system. It represents the unavailability of a system's energy to do useful work and the natural tendency of the universe towards increased disorder and chaos. This concept is central to the understanding of thermodynamics and the second law of thermodynamics, which governs the flow of energy and heat in physical systems.
Heat: Heat is a form of energy transfer between systems or objects with different temperatures, moving from the higher temperature system to the lower temperature one. It is measured in joules (J) or calories (cal).
Heat Capacity: Heat capacity is a measure of the amount of energy required to raise the temperature of a substance by a certain amount. It quantifies how much heat a material can absorb or release without undergoing a significant change in temperature. This concept is crucial in understanding the thermal properties of materials and their behavior during various thermodynamic processes.
Heat of Fusion: The heat of fusion is the amount of energy required to change a substance from a solid state to a liquid state without changing its temperature. It is the latent heat associated with the phase transition from solid to liquid.
Heat of Vaporization: The heat of vaporization is the amount of energy required to transform a substance from a liquid state to a gaseous state at a constant temperature and pressure. It is a fundamental concept that connects the topics of humidity, evaporation, boiling, heat, temperature change, heat capacity, and phase change.
Internal energy: Internal energy is the total energy contained within a thermodynamic system, arising from the kinetic and potential energies of its molecules. It is a state function and depends only on the current state of the system.
Internal Energy: Internal energy is the total kinetic and potential energy of all the atoms and molecules within a thermodynamic system. It represents the total energy contained within a system, excluding any external energy sources or work done on the system. This term is central to understanding various topics in thermodynamics, including the relationship between heat, temperature, and energy transformations.
Joule's Experiment: Joule's experiment was a groundbreaking scientific investigation conducted by James Prescott Joule in the 1840s that helped establish the relationship between mechanical work and heat, laying the foundation for the concept of the conservation of energy.
Kilocalorie: A kilocalorie (kcal) is a unit of energy equal to 1,000 calories, commonly used to measure the energy content in food and the amount of energy expended through physical activity. In physics, it is often used to quantify heat transfer.
Latent Heat: Latent heat is the energy released or absorbed by a substance during a phase change, such as the transition from solid to liquid or liquid to gas, without a change in temperature. It is the energy required to change the physical state of a substance while maintaining a constant temperature.
Latent heat coefficients: Latent heat coefficients represent the amount of heat required to change the phase of a unit mass of a substance without changing its temperature. They are crucial in understanding phase changes like melting, freezing, boiling, and condensation.
Latent Heat of Fusion: Latent heat of fusion is the amount of energy required to change a substance from a solid state to a liquid state at its melting point, without changing its temperature. It represents the energy needed to overcome the intermolecular forces that hold the solid structure together, allowing the transition to a less ordered liquid phase.
Latent Heat of Vaporization: Latent heat of vaporization is the amount of energy required to transform a substance from a liquid state to a gaseous state at a constant temperature and pressure. It represents the energy needed to overcome the intermolecular attractive forces and break the bonds between molecules during the phase change from liquid to gas.
Mechanical equivalent of heat: The mechanical equivalent of heat is the amount of mechanical energy needed to produce an equivalent amount of heat. It establishes a relationship between mechanical work and heat, quantified as 1 calorie being equal to approximately 4.184 joules.
Radiation: Radiation refers to the emission and propagation of energy in the form of waves or particles through space or a medium. It is a fundamental concept that underpins various physical phenomena and processes, including heat transfer, electromagnetic waves, and nuclear reactions.
Specific Heat Capacity: Specific heat capacity is a physical property that describes the amount of heat required to raise the temperature of a unit mass of a substance by one degree. It is a measure of a material's ability to store thermal energy and is an important concept in understanding heat transfer and temperature changes.
Stefan-Boltzmann law: The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature. This fundamental principle connects temperature and radiation, showing how hotter objects emit more energy, which is crucial for understanding heat and radiation transfer in various contexts.
Thermal Conductivity: Thermal conductivity is a material property that describes the ability of a substance to conduct heat. It quantifies the rate at which heat flows through a material when a temperature difference is applied across it, and is an important factor in understanding and predicting heat transfer processes.
Thermal equilibrium: Thermal equilibrium is the state in which two or more objects in contact do not exchange heat, meaning they are at the same temperature. No net heat flow occurs between them.
Thermal Equilibrium: Thermal equilibrium is a state where two or more objects or systems have the same temperature and no net heat transfer occurs between them. This concept is fundamental in understanding the behavior of temperature, heat, and thermodynamics.
Thermodynamics: Thermodynamics is the branch of physics that deals with the relationships between heat, work, temperature, and energy. It explores how energy is transformed and transferred within physical systems, governing the principles that dictate the behavior of matter in various states. The laws of thermodynamics play a crucial role in understanding how energy flows and changes form, influencing everything from engines to biological processes.
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Glossary
Glossary
14.2 Temperature Change and Heat Capacity