NOTES 22 - Topic 3 - Thermal Physics

1. NOTES 22 - Topic 3 - Thermal Physics ------------------------------------------------------------------------------------ 3.1.4 Temperature and Heat 3.1.1a Temperature...property that determines the direction of thermal energy transfer between two bodies in thermal contact 3.1.1b Temperature is a measure of the average kinetic energy of the molecules of a substance A.TEMPERATURE • Macroscopically...measured with a thermometer and quantified with a temperature scale; • Microscopically...a measure of the average kinetic energy of the molecules/atoms of a particular substance; B. HEAT (Q)... - natural energy transfer due to a difference in temperature (T); - transferred (moves) from a higher T to a lower T...sometimes referred to as HEATING; - may be added a system, artificially, using fire or special machinery(eg., furnace, electric heater, microwave oven, etc.); - may be removed from a system, artificially, using special machinery (eg., refrigerator, air conditioner, freezer, etc.); - measured in Joules (1.000 J = 0.2389 cal), calories (1 cal = 4.186 J), and Calories (1 Cal = 1 kcal = 4186 J ); [ There is no such condition as cold (a hit list word; also on list: cool, cooler, warm, warmer, hot, hotter, and any derivative) ...only a condition of lower temperature, less heat, or where heating has not occurred.]

2. 3.1.2 Temperature Scales...the relation between the Kelvin, Celsius, and Fahrenheit scales of temperature • The melting point (MP) of water (ice) is one major reference point; • The boiling point of water (BP) is another major reference point; • The distance between the MP and BP is divided into a “scale” of degrees; - In 1709, Daniel Fahrenheit (German physicist), marked the melting point of ice, normal human body temperature, and the boiling point of water. He then divided the span from melting to boiling into 180o. Setting the normal human body temperature as 96o resulted in the freezing point and boiling point being 32o and 212o, respectively; - In 1742, Anders Celsius (Swedish astronomer/geographer), 50 years before the advent of SI, set MP of ice @ 0o, BP of water @ 100o, and divided the distance between into 100o; - In 1848, William Thomson (Lord Kelvin) of England proposed the Absolute Temperature Scale (Kelvin Scale) which adds a 3rd reference point, absolute zero (-273 oC) and sets that as 0 K; in Kelvin scale, water’s MP = 273 K and BP = 373 K; a Kelvin degree is the same “size” as a Celsius degree; - In 1859, William Rankine (Scottish physicist), proposed an absolute temperature scale based on the Fahrenheit scale that established Absolute Zero as -459.67oF; MPwater = 491.67°R and BPwater = 671.67°R;

4. 3.1.3 Internal Energy...total of potential and kinetic energies of the atoms/molecules of a substance INTERNAL ENERGY... - includes the energy associated with the motions (KE) of the atoms/molecules; - includes vibrational KE of atoms/ molecules in a solid; - includes translational (straight-line) KE of atoms/molecules in liquids and gases; - includes potential energy of atoms/molecules due to forces between atoms/molecules (ie., state of matter...solid, liquid, gas, plasma); 3.1.4 Summary...Temperature, Internal Energy, Heat TEMPERATURE...measure of the average KE (translational) of the atoms/molecules of a substance; INTERNAL ENERGY...the sum of KE (due to all molecular motions) and PE (due to phase); HEAT...energy which naturally transfers from a higher temperature object to a lower temperature object when they are in contact;

5. 3.1.5 Define the terms mole and molar mass – 1 mole (mol) = 6.02 x 1023 molecules or atoms of a substance or element; the number of molecules or atoms needed to have a macroscopic (measureable) mass of the substance; – Molar Mass = number of grams numerically equal to the molecular or atomic mass of a substance or element when Avogadro’s number of molecules/atoms are present; 3.1.6 Define Avogadro’s Number NA= 6.02 x 1023 molecules or atoms = number molecules/atoms needed for mass of material to equal atomic mass in grams;

6. EXTRA NOTES How much volume would 1.00 mole of marbles occupy? (dmarble = 1.65 cm = 0.0165 m) 6.02 x 1023 marbles = ____________________________ m3

8. EXTRA NOTES If all the marbles were collected in space, and assumed a spherical shape because of gravity, what would be the diameter of the sphere of marbles? diametersphere = _____________________________ km diametermoon = 3480 km

9. Notes 24 3.1.7-3.1.8 Conduction, Convection, and Radiation; CONDUCTION • High T (high KE) molecules/particles collide elastically with low T (low KE) molecules/particles; • Some KE is transferred from the high T to the low T molecules/particles, causing their speed to increase; • As these collisions continue, heat energy is transferred from higher T material to the lower T material; • The result is an increase in KE and T in the second material.

10. CONVECTION • The transfer of heat energy by the mass movement of a material with a higher T (KE) over considerable distances to a region of lower T (KE); • Once transferred, further transfer of heat energy may occur through conduction;

11. RADIATION • The transfer of energy in the form of electromagnetic radiation (EMR) which does not require the presence of matter; • All bodies produce EMR in an amount directly proportional to the fourth power of their Kelvin T and their surface area; EMR α T4*A • EMR includes heat and infrared radiation; Ultraviolet radiation (UV) can cause an increase in molecular speed, KE, and T in materials which contain water.