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Conceptual Physics Study Notes & Questions: Heat and Temperature (Chap. 11)

1) Temperature is a measure of thermal energy Temperature is a measure of the average molecular translational kinetic energy in a material. It has three widely used scales: Fahrenheit (F), Celcius (C), and Kelvin (K). (p228)

2) When the average molecular translational KE goes to zero, the temperature goes to absolute zero. This is related to the Ideal Gas Law (p217): PV / T= constant. When a fixed volume of gas is cooled, its pressure go down. Scientists extrapolated at what temperature the gas pressure would go to zero, and defined that as absolute zero.

3) Materials tend to expand when heated. The amount they expand varies from one material to another; each material has its own coefficient of thermal expansion. (p232)

4) Materials have internal energy, bound up in their molecular vibrations and intermolecular attractions. Their molecules also have translational KE, which is available to transfer to other materials. These forms of energy are collectively called thermal energy. The movement of thermal energy from one material to another is called heat. (p234)

5) Simple atoms simply bounce around—their thermal energy is all tied up in their translational KE. Large complicated molecules not only bounce around, they also have many ways their constituent atoms can vibrate relative to one another—their chemical bonds act like springs. These internal vibrations also contain KE, and make up a sizeable part of the internal energy of a material. When an object is heated, the introduced thermal energy gets distributed over all available vibrational modes of the molecules. Heat capacity is a measure of how much thermal energy a material can absorb; this measure varies from one material to another and it called the material’s specific heat (p235), and it tells us how much heat 1 gram of material can absorb before its temperature is raised one degree C.

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6) Heat can also disrupt the molecular attractions that keep solids solid and liquids liquid, causing a material to change from one state to another. The thermal energy needed to change 1 gram of material from one phase to another is called its latent heat. (p238) What is this thermal energy called for melting a solid? …for evaporating a liquid into gas?

7) Heat is transferred by three mechanisms:a) Conduction (p240) –heat transferred by direct contact; that is,

by passing KE vibrations from one atom to another like a bucket brigade.

b) Convection (p241) –heat transferred by molecular motion carrying hot material from one location to another.

c) Radiation (p244) –heat transferred by infrared radiation (IR).

8) Greenhouse Effect (p245): visible light gets absorbed by materials. This EM energy gets redistributed among the many vibrational modes of molecules and re-radiates as infrared radiation. Gasses or other materials (which are transparent to visible light) reabsorb the IR radiation—trapping it in the local environment. In other words, visible light gets converted to IR radiation (i.e. heat) and gets trapped.