Physics of Technology PHYS 1800

1. Physics of TechnologyPHYS 1800 Lecture 22 Temperature

2. PHYSICS OF TECHNOLOGYSpring 2009 Assignment Sheet *Homework Handout

3. Physics of TechnologyPHYS 1800 Lecture 19 Temperature Temperature on an Atomic Scale

4. Describing Motion and Interactions Position—where you are in space (L or meter) Velocity—how fast position is changing with time (LT-1 or m/s) Acceleration—how fast velocity is changing with time (LT-2 or m/s2) Force— what is required to change to motion of a body (MLT-2 or kg-m/s2 or N) Inertia (mass)— a measure of the force needed to change the motion of a body (M) Energy—the potential for an object to do work.(ML2T-2 or kg m2/s2 or N-m or J) Work is equal to the force applied times the distance moved. W = F d Kinetic Energy is the energy associated with an object’s motion. KE=½ mv2 Potential Energy is the energy associated with an objects position. Gravitational potential energy PEgravity=mgh Spring potential energy PEapring= -kx Momentum— the potential of an object to induce motion in another object (MLT-1 or kg-m/s) Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT-1 or kg/s) and (MLT-2 or kg m/s2 or N) Pressure— force divided by the area over which the force is applied (ML-1T-1 or kg/m-s or N/m2 or Pa)

5. Dennison’s Laws Thermal Poker(or How to Get a Hot Hand in Physics) • 0th Law: Full House beats Two Pairs • 1st Law: We’re playing the same game (but with a wild card) • 2nd Law: You can’t win in Vegas. • 3rd Law: In fact, you always loose. • 0th Law: Defines Temperature • 1st Law: Conservation of Energy (with heat) • 2nd Law: You can’t recover all heat losses (or defining entropy) • 3rd Law: You can never get to absolute 0.

6. Heat • What is heat? • What is the relationship between quantity of heat and temperature? • What happens to a body (solid, liquid, gas) when thermal energy is added or removed? Thermal Energy solid Solid: Atoms vibrating in all directions about their fixed equilibrium (lattice) positions. Atoms constantly colliding with each other. Liquid: Atoms still oscillating and colliding with each other but they are free to move so that the long range order (shape) of body is lost. Gas: No equilibrium position, no oscillations, atoms are free and move in perpetual high-speed “zig-zag” dance punctuated by collisions. liquid gas

7. Heat + + + + + + + + + kB is Boltzmann’s constant =1.38 10-23 J/K

8. Physics of TechnologyPHYS 1800 Lecture 19 Temperature Measuring Temperature (0th Law of Thermodynamics)

9. What is Temperature? • If two objects are in contact with one another long enough, the two objects have the same temperature. • This begins to define temperature, by defining when two objects have the same temperature. • When the physical properties are no longer changing, the objects are said to be in thermal equilibrium. • Two or more objects in thermal equilibrium have the same temperature. • This is the zeroth law of thermodynamics. • Corollary: Heat flows from hot to cold (DUH!!!)

10. Temperature and Heat • When two objects at different temperatures are placed in contact, heat will flow from the object with the higher temperature to the object with the lower temperature. • Heat added increases temperature, and heat removed decreases temperature. • Heat and temperature are not the same. • Temperature is a quantity that tells us which direction the heat will flow. Heatis a form of energy. (Here comes conservation of energy!!!)

11. The first widely used temperature scale was devised by Gabriel Fahrenheit. • Another widely used scale was devised by Anders Celsius. • The Celsius degree is larger than the Fahrenheit degree: the ratio of Fahrenheit degrees to Celsius degrees is 180/100, or 9/5. • They are both equal at -40.

12. Temperature Ranges

14. The zero point on the Fahrenheit scale was based on the temperature of a mixture of salt and ice in a saturated salt solution. • The zero point on the Celsius scale is the freezing point of water. • Both scales go below zero. • Is there such a thing as absolute zero?

15. What is absolute zero? • If the volume of a gas is kept constant while the temperature is increased, the pressure will increase. • This can be used as a means of measuring temperature. • A constant-volume gas thermometer allows the pressure to change with temperature while the volume is held constant. • The difference in height of the two mercury columns is proportional to the pressure.

16. Absolute zero • We can then plot the pressure of a gas as a function of the temperature. • The curves for different gases or amounts are all straight lines. • When these lines are extended backward to zero pressure, they all intersect at the same temperature, -273.2C. • Since negative pressure has no meaning, this suggests that the temperature can never get lower than -273.2C, or 0 K (kelvin).

17. Absolute zero and the 3rd Law of Thermodynamics • Can anything ever get colder than 0 K? • No. • Can absolute zero ever be reached? • No.

18. Physics of Technology Next Lab/Demo: Fluid Dynamics Temperature Thursday 1:30-2:45 ESLC 46 Ch 9 and 10 Next Class: Wednesday 10:30-11:20 BUS 318 room Review Ch 10