Overview of Physics 102 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

Tentative schedule Chapter 15: Temperature, heat and expansion Chapter 16: Heat transfer Chapter 17: Change of phase Chapter 18: Thermodynamics Midterm 1 Chapter 19: Vibrations and waves Chapter 20: Sound Chapter 21: Musical sound Midterm 2 Chapter 22: Electrostatics Chapter 23: Electric current Chapter 24: Magnetism Midterm 3 Chapter 25: Induction Final 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 Macroscopic view Potential Energy contribution Kinetic Energy contribution Macroscopic view As part of internal energy Thermal energy ≠ temperature Examples

Temperature Microscopic view Macroscopic view Temperature scales 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 Newton Heat and work are both forms of energy, and we can measure both in Joules. 1 cal = 4.2 J

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 http://nooomaaas.wordpress.com/2011/10/23/the-tip-of-the-iceberg/ 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 http://www.frca.co.uk/images/bimetallic_strip.jpg 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 pearson

Thermal expansion of water Which of these statements are true? As temperature increases between 0°C and 4°C, volume is decreasing because molecules are speeding up At 4°C, the effect of ice crystals collapsing is balanced by the molecules speeding up Above 4°C, volume increases because ice crystals are collapsing. All of the above None of the above pearson

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 Specific heat table 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