PHY100S - The Magic of Physics - Class 6 - Wednesday January 25, 2006

Announcements

Debra Wunch's Monday Tutorials

Debra Wunch's Monday tutorial, previously meeting in Ramsey Wright RW229 at 6 PM, now meets in McLennan MP606 at 6 PM. This room is on the sixth floor of the tower of McLennan.

Pre-Class Quiz #2

This quiz has been marked and loaded into STORM. The class average was 88%. Well done!

Six students entered student numbers that do not correspond to students enrolled in this course according to STORM:

993356707
992984543
992420448
994417886
993357292
981899430

These people, and any other people who believe they have a problem with their mark on this quiz, should see April Seeley, afternoons in MP129.

Reminders

• On Monday January 30, Homework #3 and the Short Paper are due in the Drop Box for your tutor by 5 PM.
• The class on Monday January 30 will begin with Pre-Class Quiz #3
• This Friday is the last day to see April Seeley in MP129 about any problems with your mark on Pre-Class Quiz #1.
• Please bring a soft-lead pencil to class on Monday.

Today's Class

We continue to be about one textbook section behind the syllabus' schedule. We still have to talk about §7.4.

An Analogy to Conservation of Energy

As you probably know, from 1985 to 1995 a very popular comic strip was Calvin and Hobbes by Bill Watterson. It is currently being re-distributed. In the comic a little boy named Calvin specialises in being bad. His best friend is a toy tiger named Hobbes, who only becomes alive when alone with Calvin. Let us imagine that Calvin has a collection of toy blocks, and every night after he goes to bed his parents pick up the blocks scattered all over the house and put them in the toy box. They notice that every night they end up with the same number of blocks. So they begin thinking about a concept of conservation of blocks.

One night after they have collected all the blocks they notice that they are 2 blocks short. But they look out the window and see 2 blocks in the back yard. So they now have 2 terms in their definition of the number of blocks:

Each night the number in the toy box and the number in the back yard may change, but their sum is always the same number. So the principle of conservation of blocks is preserved.

A couple of weeks later the number of blocks in the toy box plus the number in the back yard is one less than the previous night. But they notice that Hobbes' stomach is a little distended. Of course they can't cut Hobbes open and see if he has swallowed a block. But they are clever (for parents) and weigh him. His weight has increased by the weight of one block. So now there is a third term in their calculation of the number of blocks:

Note the analogy to the concept of Conservation of Energy. We started out saying that the kinetic energy KinE, one-half of Leibniz's vis viva, was conserved in some collisions. We then added a second term, the gravitational energy GravE, and said that GravE plus KinE was conserved. In the 1840's a third term was added to the total energy, thermal energy ThermE. As time goes by we keep adding terms to our equation, but the overall conservation law is preserved. Also note that each term in the equation involves a measurement and perhaps a calculation.

Chapter 7 - Thermodynamics

We played a 2-minute fragment of a song by Flanders and Swann that appeared on the album At The Drop of Another Hat (1964). The full version is available in mp3 format via the button; running time is 4:13 and the file size is 3.9M.

Other Class Materials

We asked some questions in class, available via the button. Separate window.

Here is today's Journal file in pdf format. Separate window.