 Physics Honors/AP 1 and 2

#### Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content. Homework

# Physics 15: 7-12 Entropy

## Homework

### Reading Preparation

Text Reading: Giancoli, Physics - Principles with Applications, Chapter 15: Sections 7 to 11.

##### Study Points
• Section 7: Entropy is a measure of order or disorder in a system. Since it is a state function like potential energy, we can only measure its change, not its absolute value. We do this by dividing the amount of heat energy change divided by the temperature at which the change occurs: ΔS = Q/T. In an isolated system, the total entropy can remain the same or increase, but it can never decrease.
• Section 8: Because heat flows from disordered to ordered systems, increasing the heat content of ordered systems and randomizing motion by introducing greater disorder, the tendency is for the universe to move toward a state of greater disorder. Entropy increases.
• Section 9: Every natural process results in some loss of useful energy to heat energy. Useful heat energy is converted to work energy, which lowers temperatures; lost heat energy randomizes motion, which increases temperatures and entropy. When everything is the same temperature, there will be no heat flow, and no further work can be done. The universe will suffer heat death.
• Section 10*: One way to visualize entropy is to look at all the states a system can have, and identifies those that are "ordered". In this type of analysis, it is easy to see that most systems with even a few elements have more "disordered" than "ordered" states. If we increase the number of components in the system, the number of disordered states increases more quickly than the number of ordered states, so the more complex the system, the greater the probability that a random change will increase entropy.
• Section 11*: The tendency to increase entropy can't be avoided, but the rate at which a particular process increases entropy can be used to determine more efficient, lest wasteful processes in energy conversion.

• Entropy

### Web Lecture

Read the following weblecture before chat: Inertia, Acceleration, and Force

### Study Activity

Use the Plink probability simulator to explore probability and statistics in system. Run the introduction several times to get a sense for the distribution of balls. Then use the lab to see how changing the number of rows and the binary probabily shifts the distribution.

Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.

Optional Websites:

Physics for Idiots site gives a very basic definition of the concepts required for thermodynamics and is a useful check for your understanding of these simple but profound ideas.

### Chat Preparation Activities

• Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

### Chapter Quiz

• Required: Complete the Mastery exercise with a passing score of 85% or better.
• Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!

### Lab Work

If you want lab credit for this course, you must complete at least 12 labs (honors course) or 18 labs (AP students). One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!