Lecture 15: Temperature and Heat

Vocabulary practice covering temperature scales, heat transfer mechanisms, specific heat capacity, and thermal expansion concepts from Lecture 15.

Temperature ($T$)

A physical quantity that defines the average kinetic energy of an object and quantifies its hotness or coldness.

Empirical Scale

A type of temperature scale, such as Fahrenheit or Celsius, where experiments are performed to derive the upper and lower limits of the scale.

Fahrenheit Scale

An empirical scale proposed in the 1700s using a frozen salt water solution as $0$ and human body temperature as $90$, with $89$ gradations in between.

Celsius Scale

A scientific scale developed in the 1700s where $0\,^\circ\text{C}$ is established by the freezing point of water and $100\,^\circ\text{C}$ is established by the boiling point of water at one atmosphere of pressure.

Absolute Scale

A temperature scale designated by establishing the lower limit based on the physical limitation known as absolute zero.

Absolute Zero

The lowest possible temperature that can be achieved, establishing the lower limit of absolute scales; it is equal to $-273\,^\circ\text{C}$.

Kelvin Scale

The established SI unit for temperature where the zero end is absolute zero and a change in one Kelvin is equal to a change in one degree Celsius.

Celsius to Fahrenheit Conversion

To convert from Celsius to Fahrenheit, multiply the Celsius temperature by $1.8$ and add $32$: $T_{F} = (1.8 \times T_{C}) + 32$.

Fahrenheit to Celsius Conversion

To convert from Fahrenheit to Celsius, subtract $32$ from the Fahrenheit temperature and multiply the result by five-ninths: $T_{C} = \frac{5}{9} \times (T_{F} - 32)$.

Heat ($Q$)

Energy that is transferred from one object to another in response to a difference in temperature, spontaneously flowing only from hot to cold.

Calories

The primary unit used in this class to measure heat energy, although Joules are also a valid unit for energy.

Specific Heat Capacity ($c$)

Often described as thermal inertia, it defines how many calories of heat are required to increase or decrease the temperature of a certain mass of material by a certain amount.

$$Q = mc\Delta T$$

The equation used to relate heat ($Q$) in calories, mass ($m$) in grams, specific heat capacity ($c$), and temperature change ($\Delta T$) in degrees Celsius.

Specific Heat Capacity of Water

A value of $1\,\text{cal}\,\text{g}^{-1}\,^\circ\text{C}^{-1}$, which is high compared to common substances, making it effective for cooling systems and climate moderation.

Thermal Equilibrium

A state where two or more mixed substances reach a constant temperature readout, indicating no further net flow of heat between them.

Conservation of Energy (Heat)

The principle that, assuming no heat is lost to the environment, the heat entering a cold substance must equal the heat leaving a hot substance: $Q_{hot} + Q_{cold} = 0$.

Expansion Joints

Engineering features in long bridges that account for thermal expansion, enabling structures to stretch in the heat without buckling or breaking.

Northeast Blackout of 2003

A historical event where thermal expansion of power lines due to heat and high electrical load caused short circuits when lines contacted tree limbs.

Bimetallic Strip

A device made of two different metals connected together that curls when heated because each metal expands at a different rate, utilized in analog thermostats and cooling systems.

Negative Thermal Expansion

A phenomenon where a substance contracts when heated, such as water when it is below its maximum density temperature of $4\,^\circ\text{C}$.

Thermal Stress

Internal force caused when the molecules in an object are not given enough time to respond to rapid expansion or contraction, often leading to structural failure like breaking glass.

Pyrex

Specially tempered glass used when wide swings of temperature are expected over short periods to prevent breaking due to thermal stress.