Glossary
Atomic Collisions
The microscopic interactions where higher-energy atoms or molecules transfer kinetic energy to lower-energy atoms or molecules, leading to heat transfer.
Example:
In a hot metal rod, energetic atoms vibrate and collide with less energetic neighbors, transferring energy through atomic collisions.
Conduction
The transfer of thermal energy through direct contact between particles, without any net movement of the material itself.
Example:
If you touch a hot metal spoon, the heat transfers to your hand primarily through conduction.
Convection
The transfer of thermal energy through the movement of fluids (liquids or gases) that carry heat with them.
Example:
A radiator heats a room by warming the air, which then circulates throughout the room, demonstrating convection.
Cooling
The process by which energy leaves a system via thermal processes, typically resulting in a decrease in the system's temperature.
Example:
An ice cube melting in a drink causes the drink to experience cooling as the ice absorbs thermal energy from it.
Direction of Energy Transfer
Thermal energy always spontaneously flows from a region of higher temperature to a region of lower temperature.
Example:
When you open a refrigerator door, cold air doesn't flow out to warm the room; instead, warmer room air flows in, illustrating the direction of energy transfer.
Fourier's Law
A fundamental law describing the rate of heat transfer through conduction, stating that the rate is proportional to the negative temperature gradient and the cross-sectional area, and dependent on the material's thermal conductivity.
Example:
Fourier's Law can be used to calculate how quickly heat escapes through a window pane on a cold day, given its material properties and temperature difference.
Heating
The process by which energy enters a system via thermal processes, typically resulting in an increase in the system's temperature.
Example:
Placing a pot of water on a stove burner causes the water to undergo heating, as energy is transferred from the burner to the water.
High Thermal Conductivity
A characteristic of materials that allow heat to transfer through them very efficiently and quickly.
Example:
Metals like aluminum exhibit high thermal conductivity, making them ideal for heat sinks in electronics.
Linear Expansion Coefficient (α)
A material-specific property that quantifies how much a material's length changes per unit of original length per degree Celsius or Kelvin change in temperature.
Example:
Steel has a specific linear expansion coefficient (α), which engineers use to design railway tracks with appropriate gaps to prevent buckling.
Linear Thermal Expansion
The change in length of a material due to a change in temperature, proportional to its original length and the temperature change.
Example:
A long metal bridge will undergo linear thermal expansion, becoming slightly longer on a hot summer day compared to a cold winter day.
Low Thermal Conductivity
A characteristic of materials that resist the transfer of heat, making them good insulators.
Example:
Styrofoam cups have low thermal conductivity, which helps keep your hot drinks warm and your cold drinks cool.
Radiation
The transfer of thermal energy through electromagnetic waves, which does not require a medium.
Example:
The warmth you feel from a campfire, even from a distance, is primarily due to radiation.
Thermal Conductivity (k)
A material property that quantifies its ability to conduct heat; a higher 'k' value indicates a better conductor of heat.
Example:
Copper has a high thermal conductivity (k), which is why it's used in cooking pots to quickly and evenly distribute heat.
Thermal Contact
A state where two systems are able to exchange energy through thermal processes, allowing heat to flow between them.
Example:
When you place a cold can of soda on a warm table, they are in thermal contact, and heat will begin to transfer from the table to the can.
Thermal Equilibrium
A state where two or more systems in thermal contact have reached the same temperature, resulting in no net transfer of thermal energy between them.
Example:
After a hot cup of coffee sits on a table for a long time, it eventually reaches thermal equilibrium with the surrounding room, becoming room temperature.
Thermal Expansion
The tendency of matter to change in volume, area, or length in response to a change in temperature.
Example:
Concrete sidewalks often have gaps between sections to allow for thermal expansion on hot days, preventing cracking.
Thermal Processes
The fundamental mechanisms by which thermal energy is transferred between objects or systems: conduction, convection, and radiation.
Example:
The warmth you feel from the sun is due to thermal processes, specifically radiation, while boiling water involves convection.
Volumetric Expansion Coefficient (β)
A material-specific property that quantifies how much a material's volume changes per unit of original volume per degree Celsius or Kelvin change in temperature.
Example:
The volumetric expansion coefficient (β) of mercury is why it was historically used in thermometers; its volume changes predictably with temperature.
Volumetric Thermal Expansion
The change in volume of a material due to a change in temperature, proportional to its original volume and the temperature change.
Example:
When a balloon filled with air is heated, the air inside experiences volumetric thermal expansion, causing the balloon to inflate slightly.