Homework on atoms and temperature; due Friday, Feb 6

This HW is due at the start of class on Friday (Feb 6), the day of our 2nd quiz. Doing these problems should also be good preparation for the quiz (and for the midterm on Feb 11).

Also, this week there will be an extra homework help section at 2 PM Wednesday in ISB 339.

1. What are atoms made of?

2. What components of an atom are most important in establishing its mass?

3.a) How does the mass of an oxygen atom compare to that of a hydrogen atom? How does it compare to that of a proton?

b) How does the mass of an carbon atom compare to that of a hydrogen atom?

c) How does the mass of an neon atom compare to that of a hydrogen atom?

d) How does the mass of an helium atom compare to that of a hydrogen atom?

4. a) What is deuterium? b) How does the mass of an carbon atom compare to that of a deuterium atom? c) Hydrogen is much more abundant than deuterium, but there is something about H that is a little odd or unconventional, regarding its nucleus, compared to that of other light elements. What is it?

5. What is the mass of an H2O molecule? What is the mass of a D2O molecule?

6. Thinking about the size of atoms:
a) Which is bigger: H or He?
b) Which is bigger: Li or O ?
c) Which is bigger: O or Ne ?

7. Why is it more difficult to explain the size of atoms than it is to explain the mass of atoms?

8. What part of the atom determines its size?

9. Suppose the average speed of an oxygen molecule in air at "room temperature" is 600 m/s. Would the average speed of a nitrogen molecule be the same, less or greater?
How about the average speed of a hydrogen molecule or a helium atom? Explain your reasoning briefly.

10. Suppose the average speed of a helium molecule in a gas is 500 m/s at -73 C. You add heat and observe that the average speed goes up from 500 m/s to 1000 m/s. What is the new temperature of the gas? [Give your answer in both C and K temperature scales.] Explain your reasoning briefly.

11. Suppose the average speed of an oxygen molecule in air at "room temperature" is 600 m/s. What is the average speed of a helium atom in that air?

Matter and Atoms

Most matter is made up of atoms. That includes gases, like He or air, where atoms are free and go zipping around with an average speed proportional to the square root of the temperature of the gas (see post on heat and T); solids where atoms are stuck together on a semi-rigid lattice; and the in between state called liquids where atoms are close together, like atoms in a solid, but have a sense of disorder, freedom and flow reminiscent of the gas state.

All known atoms can be presented in something called the Periodic Table of Elements. This organizes the elements in a profound and amazing way. Some degree of familiarity with the nature of the periodic table and its organizing principles is an essential part of your education.

One of the puzzling things we noticed about atoms has to do with their size. The size of an atom is determined by its electrons, but it does not increase in any simple or systematic way with the number of electrons in the atom. For example, Hydrogen, which has one electron, has a radius of about 0.1 nanometers (nano means 10^-9). Neon, which has 10 electrons, also has a radius of about 0.1 nanometers --about the same as Hydrogen. The graph of atom size (radius) as a function of its number of electrons is very interesting and perplexing. This is a nice graph to be familiar with and to appreciate the subtlety of its origins, which lie in the wave theory of the electron (Edwin Schrodinger, 1928).

This complex and interesting behavior of the size of atoms contrasts with the relative simplicity of the mass of atoms, which is basically equal to the number of protons and neutrons in the nucleus of the atom time the mass of a single proton (or neutron), which is 1.67 x 10^-27 kg. All this mass is concentrated in very tiny nucleus, which is much much smaller than the size of the atom. So an atom consists of a positively charge nucleus which is very tiny but contains essentially all the mass of the atom, surrounded by a light, wave-like electron.

Heat and temperature

"Heat" is the title of Part 3 of our class book which starts with chapter 15. For that chapter (15), I would suggest trying to answer problems 1 ,2 ,3 and 5. For chapter 16, I think review question 1 provides a good point of focus. Heat is energy. Putting heat into something makes it warmer; it increases its energy content and its temperature. Temperature is actually not such a simple concept and it is surprisingly difficult to come up with a general definition for temperature. For gases it is proportional to the kinetic energy of the molecules or atoms that make up the gas. Temperature is something that when it is the same, between two materials, no energy will flow from one to the other. We call that thermal equilibrium. Actually creating such a quantity leads to some subtle and somewhat tricky math involving exponentials, logarithms and Taylor series expansions.

For this class what you should know two things:
1) the "phenomenological definition": T is the quantity which, when equal between two materials leads to zero heat flow (equilibrium), and when not equal between two materials the amount of heat flow (energy which goes from one material to another per second) is proportional to the temperature difference.
2) for a gas, the temperature is proportional to the average kinetic energy of the molecules of the gas.

Online Work. PLEASE READ!!!

Okay, I know a lot of you have been having trouble with the online work. We've worked out a couple of things.

1) All online quizzes & tutorials assigned thus far will have a new deadline of February 10. If you've done everything ontime already, then you've been prepared for the homework and quizzes, and if you've had trouble, then now you can catch up.

2) Two of the previously assigned tutorials do not have the option to be saved! If you've had trouble with "Newton's Third Law" and/or "Vectors", then it's not your fault.

To summarize:

Tutorials: "Parachuting and Newton's Second Law", "Momentum and Collisions", "Energy", Projectile Motion", and "Orbital Motion".

Quizzes: As far as I know, the quizzes from each chapter ARE recordable. Quizzes assigned so far are from chapters 2, 3, 4, 5, 6, 7, 10.

3) Please make sure you are signed up for our class! On the left-hand side of links, at the top, you might see a link "Join A Class". If you haven't done so, click that, and enter our class code cm799640.

I'm sure there are bound to me more problems, please let me know as soon as possible so I can try and help, thanks.

-Eliot

Quiz Solutions and Discussion (Quiz 1)

These two pages provide a guide to our quiz from last Friday. This much longer than what you were expected to do on the quiz, and provides some insight into the thinking behind the questions and their solutions.

For the first problem the most important thing was go a nice graph for (b), with labels and scales, and, for (a), to realize that being at the highest point of the motion corresponds to having zero speed, and that it takes 1 second to slow down from 10 m/s to zero under the influence of gravity.

The second problem was a conservation of energy problem and you needed to use P.E.= mgh and the expression for K.E. in terms of m and v.

The third problem(extra credit) involves competing considerations --time of flight and launch speed. [It is analogous to the problem regarding the optimal angle for a cannon..., which is governed by the same considerations (time in the air and horizontal speed).] Identifying those two considerations, and the qualitative nature of their dependence on s, is the key thing for problem 3.

Help section tonight, 6 PM -highly recommended!

There will be a very excellent help section this evening at 6 PM. It will help you with your homework and with your preparation for the quiz. I strongly recommend going to that. It is in Nat Sci. (Annex) 101. -Zack

Quiz notes

The quiz will be fairly short; there will be 2 or 3 questions. One will be on conservation of energy. Another will probably be on vertical motion under the influence of gravity. There will be some graphing. When you create graphs it is important to: 1) label your axes, 2) scale your axes, and 3) indicate units next to the label. For example, y (meters) could be the label (with units) for the vertical axis of a graph of y vs time. t (sec) could be the label for the horizontal axis. Scale your axes means put some numbers and tic marks (not too many, just 2 or 3 per axis is usually just right). Typically, the size of your graphs should be about 3x3 inches.

Please feel free to post questions or initiate discussion here.

home work 1 solutions

click on the pages to make larger

Reading - January 17-24

Consistent with the content of this weeks homework, your current reading should emphasize chapters 7 and 10. Those chapters have some very helpful tutorials and interactive figures that I would recommend. The concept of energy plays a central role in physics and related disciplines and is worth a lot of attention.

Looking ahead to the next section of the book --properties of matter-- our emphasis there will be on material related to chapter 11. Chapters 12-14 can just be lightly skimmed.

Please feel free to post any comments or questions here.
-Zack

Homework 2

For homework 2, please do the following book problems:
Ch 6: Problems 5 and 7
Ch 7: Problems 4 and 9 and
*Calculate how much energy it requires to ride a very efficient bicycle up a hill for which the elevation change is 300 meters. Assume the bike has a mass of 10 kg and the person has a mass of 50 kg. Extra credit if you calculate this in joules (the default) and then convert that into kilocalories, which are what is conventionally refer to as calories when describing the energy content of food.
Chapter 8: Problems 4 and 5 (see interactive figure 8.18, Torque and Equilibrium)
Ch 10: Excercises 2, 3, 11, 34 and Problems 1 and 3*
*double credit for "the bike problem" and problem 3

as well as the following on-line work at the Pearson "10e" site:
tutorial on energy (Ch 7)
tutorial on projectile motion (Ch 10)
tutorial on orbital motion (Ch 10)
the tutorials on Black Holes and on Tides are extra credit. (They seem very interesting.)

Also at the Pearson site please do the END OF CHAPTER quizzes (these are under "chapter features").
Chapter 7 ( the answer to 7 is 0.25)
Chapter 10: (the answer to 7 is "yes both would increase)

This is due next Friday. Please post any questions here for quick, cogent answers and discussion. Questions, and responses to questions, are appreciated.

Homework 1

Homework 1 includes both book problems and online work at the Pearson web site. The online work must be completed by 11:30 AM on Friday, Jan 16th. For your solutions to the book problems please show your work and make it very neat and well-organized. Clarity and good presentation is required. These are due in-class that same day (Jan 16). The book problems are as follows:
Chapter 3: Excercises 20, 21, 34 and 45 and Problems 3, 4 and 5.
Chapter 4: Problems 2, 6 and 7.
Chapter 5: Problem 3.
Chapter 6: Excercise 45 and problem 6.
Please feel free to post any questions regarding the book problems here and to answer, discuss or nuance other peoples posts.

The online work includes:
the end of chapter quizzes from chapters 2 through 6,
the tutorials associated with chapters 2-6, i.e., Newton's 2nd Law, Newton's 3rd Law, Vectors, and Newton's 3rd Law and Momentum.

Questions, comments and discussion regarding the online work is also welcome here.

Powerpoint from Jan 10th class

Here are images of a powerpoint related to what we will cover in today's class.

Textbook/Website Information

Here's some info on registering for the website regarding the textbook.

To register, go to
http://wps.aw.com/wps/media/access/Pearson_Default/5632/5768114/login.html
or just google "media 10e" (and select the 1st result), and follow the steps to register.

You'll need an Access Code to complete this.
If you've purchased the Media Update 10e copy of the textbook, the code is included there.
If you have any other edition of the text, that's fine. You can purchase the Media Update without the book online:

https://register.pearsoncmg.com/reg/buy/buy1.jsp?productID=34427

This is only $30, and includes an e-copy of the book online.
However, be aware. Homework problems Zack assigns from the text will correspond to 10th Edition. If you use an older version, you'll need to look at the e-copy to find the correct problem.

You'll also need the class number to register, which is:
Class ID: cm799640

If there are any questions with this, whatsoever, please post them, as you can be sure you're not the only one having the same problem.

-Eliot

Reading

Our first classes will deal with material from Chapters 2-10, the chapters on motion (mechanics). Reading from those chapters, in that order, should be relevant to what we will cover in class over the next week. Also, I have found the interactive online figures to be excellent, for the most part, and recommend playing with those. Additionally there are online tutorials available (e.g., Newton's 2nd Law, Newton's 3rd law, ... and Momentum, Energy...), which i think are helpful (and will be part of the first HW (wich will be officially posted tomorrow)). The first HW will also include the quizzes from most of these chapters. Please feel free to pose questions about the material, raise discussion topics, and contribute generously to discussions via "comments" to this post.

Welcome to Physics 1

Hi. Welcome to Physics 1, Conceptual Physics. The first jpeg document here has some basic information and a brief discussion of the class. The second one is an image of the powerpoint from our 1st class meeting.