What is temperature?

It is different than heat and thermal energy.

Temperature is what thermometers measure. It is an indication of the internal kinetic energy of the object.

The kelvin scale uses 0 K as the absolute zero temperature. It is related to the celsius scale by

Thermal energy is the sum of the internal potential and kinetic energies of all the atoms and molecules of a body.

We measure energy in the SI unit of joules. In more common use is calories.

cal = calories

J = joules

1 cal = 4.186 J

1 calorie is the amount of heat required to raise the temperature of 1 g of water by 1 ⁰C.

1 Calorie = 1 kcal

Calorie is the food energy unit.

Specific heat capacity refers to the ability of a substance to store thermal energy.

Units: cal/g ⁰C

See table on page 300

How is energy transferred?

Conduction

Convection

Radiation

Phase Changes

As we go up the temperature scale:

Melting, evaporation (or vaporization).

As we go down the temperature scale:

Condensation, freezing (or solidification).

Some substances skip a phase: sublimation goes from solid to gas like CO₂.

Latent heat of fusion is the energy required to transform from solid to liquid. 80 cal/g for water.

Latent heat of vaporization is the energy required to transform from liquid to gas. 540 cal/g for water.

When the phase change goes in the opposite direction, negative values of energy occur. When water freezes, energy is released.

Evaporation is not the same as boiling. Evaporation takes place at the surface of the liquid. It takes energy to evaporate the molecules, and the object then feels cooler. That is why we sweat.

 Zeroth law: Two bodies in thermal equilibrium with a 3^rd body are in thermal equilibrium with each other.

First law: Energy is conserved in all transformations in an isolated system.

Second law: Within an isolated system, some (but never all) heat from a source can never be converted into work or mechanical energy.

Heat input = work output + waste heat output

Heat engines extract heat from a hot reservoir, does work, and expels part of the heat to a colder reservoir.

See figure on page 339.

Maximum Efficiency = (T_hot - T_cold)/T_hot

can never be 100%

Internal combustion car engines are examples of heat engines.

Second Law has several forms: heat flows spontaneously from a hotter body to a colder body, never the other way around.

Heat pumps require work to take heat from a cold body and remove it to a warm body. Refrigerators, freezers, and air conditioners do this.

Entropy: the entropy of an isolated system never decreases.

 Conceptual Ideas

Difference between Temperature and Heat

 Temperature Equalization

 Development of a Model

 Characteristics of a Model

 Specific Heat

 Latent Heat of Fusion

 Latent Heat of Vaporization

 Increasing Disorder

 Heat Conductors and Insulators

 Other Forms of Energy