Structure:•Phys 101 not needed for this class •Focus on concepts• Lecture/lab format• Interactive: experiment and observation

Exams:• 3 midterms, 1 comprehensive final• Lowest exam score dropped• Chance to make up some points through exam review

Homework:• Reading questions: due online day before class• Problems from book: due the class period after we finish chapter

Overview of Physics 102

Tentative schedule

Chapter 15: Temperature, heat and expansionChapter 16: Heat transferChapter 17: Change of phaseChapter 18: ThermodynamicsMidterm 1

Chapter 19: Vibrations and wavesChapter 20: SoundChapter 21: Musical soundMidterm 2

Chapter 22: ElectrostaticsChapter 23: Electric currentChapter 24: MagnetismMidterm 3

Chapter 25: InductionFinal exam

Activities

• Do “Initial Ideas on Heat and Thermodynamics”

• Do “Initial Questions about temperature, heat, entropy, thermal energy”

• Do Assignment 1

(see PH 102 folder on G drive)

Perspective on heat and thermodynamics

(see Course Outline page 5)• Aspects of motion• Consequences of vast numbers of constituent parts

•Instead of keeping track of the trajectory of each atom, a substance can be described in terms of macroscopic properties such as temperature, pressure and volume.

• Three basic concepts to define and differentiate:•Thermal energy•Temperature•Heat

Thermal Energy

•Microscopic view•Thermal energy

•Potential Energy contribution•Kinetic Energy contribution

•Macroscopic view•As part of internal energy

•Thermal energy ≠ temperature•Examples

Temperature

•Microscopic view•Proportional to average random translational kinetic energy per particle (absolute, e.g. Kelvin)

•Macroscopic view•There is a qualitative notion of hot and cold, which we measure with temperature

•Temperature scales•History•Definitions °C, °F, K•Thermometers

Do: Predictions/Notes Kinetic Theory of Gases,

Simulation: http://phet.colorado.edu/en/simulation/gas-properties

Thermal expansion

•Material expansion due to temperature increase•Reasons for•Mathematical definition•Examples

•Bimetallic strips•Metal rods•Holes (recall Assignment 1)

•Exceptions

•H20

•Long chain molecules

Heat

•Definition: energy transfer by virtue of a temperature difference between units•Heat ≠ Temperature•Specific heat

•Heat exchange and existence of specific heat•Reasons for differences in specific heats•High specific heat of H2O•Specific heat related phenomena

•Weather•Common experiences

•Heat ≠ thermal energy•Do “specific heat” lab•Examples

Energy units

Heat energy is traditionally defined in calories.

1 cal = heat needed to raise the temperature of 1 gram of water by 1°C.

1 Cal = 1000 cal

If you capitalize calorie, it means something different. These are called food Calories. You need to eat about 2000 Calories per day.

Work is defined in physics as energy required to move a massive object or substance. Work is traditionally measured in Joules.

1 J = work done in moving 1 meter against a force of 1 NewtonHeat and work are both forms of energy, and we can measure both in Joules.1 cal = 4.2 J

http://antwrp.gsfc.nasa.gov/apod/image/0711/aurora_mcvay.jpg

Kinds of motion

There are a lot of ways molecules can move. They can change their positions (translation). They can also rotate, vibrate, twist and move in other complicated ways.

Temperature involves translation only. When molecules are moving faster on average, the temperature is higher. It is an intensive property - it does not depend on the amount of the substance involved.

Internal energy involves all kinds of motion of molecules, including rotation, etc. It is an extensive property - it does depend on the amount of the substance involved.

Temperature vs. Thermal Energy

Temperature does not measure the total thermal energy of a substance. A swimming pool and a goldfish bowl can be the same temperature but the swimming pool has much more thermal energy. In both cases, the total thermal energy is the sum of the kinetic and potential energies of all of the molecules.

Temperature vs. Thermal Energy

Which has higher temperature, an iceberg or a cup of tea?

Which has higher thermal energy, an iceberg or a cup of tea?

Temperature scales

Three temperature scales are in use today. Celsius (or Centigrade) is based on water. The freezing point of water is 0°C and the boiling point is 100°C. The Kelvin scale uses the same size for its degrees but shifts its zero to absolute zero (-273°C). On the Fahrenheit scale, the freezing point of water is 32°F and the boiling point is 212°F.

Thermal expansion

Most substances expand with heat. When they expand, they retain their proportions. The amount of expansion for a given change in temperature is a property of the substance - different substances expand different amounts. This explains why heating a jar lid will make it easier to open the jar. The metal lid expands more than the glass jar under the hot water.

Bimetallic strip

Bimetallic strips bend because one metal expands more than the other for a given change in temperature. They are often used in thermostats.

Thermal expansion of water

Thermal expansion of water

Which of these statements are true?

A. As temperature increases between 0°C and 4°C, volume is decreasing because molecules are speeding up

B. At 4°C, the effect of ice crystals collapsing is balanced by the molecules speeding up

C. Above 4°C, volume increases because ice crystals are collapsing.

D. All of the aboveE. None of the above

Heat vs. temperature

In everyday language, heat and temperature mean roughly the same thing. In physics, these two commodities are quite different. Temperature is related to the average speed at which molecules move. It is an intensive property - it does not depend on the amount of substance present. If something is hot, it means the molecules are moving fast. Something cold has slowly moving molecules.

Heat

Heat is energy transferred because of temperature differences. It is neither intensive nor extensive - it is the quantity of energy in transit.

Heat exchange

When two materials are in contact, they exchange heat until they come into thermal equilibrium. The heat lost by one is gained by the other until they are the same temperature.

Specific heat

Specific heat capacity is defined as the amount of heat needed to raise the temperature of a substance by 1 degree Celsius. Different substances have different capacities for storing internal energy, so applying the same heat to two substances can result in them having different temperatures, even if they have the same mass.

Specific heat of water

Water has a very high specific heat - it takes a lot of heat to raise its temperature. This is especially important for life on Earth. Water must lose a lot of heat to lower its temperature. That means oceans are very hard to freeze.

Specific heat table