Absence Monday 1/31

As much as I would like to return my cold germs to whomever of you saw fit to share them with me, my conscience is preventing me from sharing them with the rest of you, i.e. I will be out today. If you read this Monday morning and you are in honors, bring the fusion notes with you, to read in class. There will be a set of questions for you to answer as groups.

AP Section 4, please continue with the harmonic motion lab. Both AP classes will have a worksheet to be done as groups.

Honors Standing Wave Lab

It is a little discouraging to see how many lab reports come in with errors after a post which spells it all out is up on the blog. The next time your failure to get things right the first time compels me to post an explanation of the lab, your grade on resubmitted labs will be mud if you show you failed to read the post.

Honors Labs

There is simply too much similarity between labs, especially considering they contain the same very odd errors. For example, a large number of labs showed graphs of lambda vs c with the title frequency = lambda/c. They all showed the same slope and none of them described what the slope meant. Since they were all wrong in the same very silly way and since none of the labs said why the graph was made or what it meant, I can only assume it had one source and the rest were copies, made by students who could not be bothered figuring things out for themselves. I hope there is an alternate explanation.

You are allowed to do labs together, but you must show individual writing and thinking. If you don't understand it don't copy it and turn it in as your work.

If an incident such as this occurs again it will be treated as plagiarism with appropriate zeros awarded and other action taken. More important, I will just stop trusting you.

By the way, frequency = c/lambda and therefore equals 1/slope of your graph

Another odd thing that turned up in several labs is that c increases by, or perhaps 1.5 x as great if tension is doubled. I am sure your math teachers wold be less than gratified to hear you think square root of 2 = 1.5. I conclude a lot of copying happened here as well.

Honors Fusion Notes

We are beginning our next adventure, the exploration and design of a fusion power plant.

Begin with reading the following notes. Also look for a few wave problems in a post coming soon.

http://h1.ripway.com/DrCherdack/Fusion%20NotesR2.doc

http://h1.ripway.com/DrCherdack/HoffmanonFusion.doc

Honors Sect 2 Mid year Review

I have 3 packages with no name on them.

I am missing packages from Nicole, Brad, Michael, Divya, Billy, Jamie, BonBon and Peter. If you turned one in, email me with a description of your package so I can give you credit.

Missing Assigments

This year has been the worst ever in terms of stuff not being done or turned in. I guess I should be glad to see how many of you don't really care about grades. However, it would be nice for you to do the work in order to learn.

Many labs are still missing. The chart posted on 1/14 showed which labs needed to be turned in.

Study group reports are missing from many of you. Since not giving you a grade will not be feasible in this grade crazy environment, I will just make deductions in the grade you will receive. Required means required not optional.

In one class, the midyear review assignments were not turned in at all. In others many were missing. The equivalent of four home works will be lost.

Honors project reports are missing from about half the groups. There goes about 1/2 of your project grade.

Circular motion

Centripetal force is not a force. It does not belong on free body diagrams. It is merely a label applied to that portion of the net force which points toward the center around which an object is rotating.

Midyear Exams

Results for many were not bad at all. However, most of you continue to make the same fundamental errors. I believe this goes to the very root of what is wrong with the way most of you learn. You are still looking for the simplest combination of numbers to get an answer without understanding the physical relationships behind the equations.

For example, faced with a cart going down a hill most of you stick what is PE initial in an equation which requires delta PE. You may actually write Delta PE in your equation, but you use just PE initial. This is because delta PE requires two numbers and so is too hard for your brain.

When you come down a hill delta PE = mg (h at bottom - h at top). I would hope that high school juniors in AP or honors classes would know that h at the bottom - h at the top is a NEGATIVE number. In other words, I would hope that you would know which way is up! and therefore which way is down.

Another very common error involves acceleration in rotational motion. When at the top of a curve, one can assume that you got there by going up and are leaving by going down. This means that your velocity is changing from up to down which means your acceleration is down or negative. Another instance where you demonstrate whether or not you know which way is up! However, adding a negative sign is apparently an extremely laborious process which you are not willing to undertake.

Many of you are showing a complete disregard for what conservation of momentum means by writing m1v1=m2v2. This is almost never true. If total momentum is zero in a system with two objects in it then m1v1= - m2v2 before and after any collisions or other interactions between the two. However, this is not true if the total momentum is not zero. You should start with the full blown m1v1+m2v2= m1v1'+m2v2'.

Many of you still writing Funknown = Mg even when there is acceleration and you should use Funknown =Fnet -(Fknown) [Fknown is -Mg in many vertical cases]. Also Funknown = Fnet is WRONG when there are other forces acting such as gravity. In other words, you frequently use incorrect equations just because they have one term on the right side instead of the two terms the correct equations have.

Finally, for now anyway, is the fact that you incorporate Mg in equations concerning horizontal motion. This is wrong, usually for two reasons. One, Mg is a vertical force and does not cause horizontal acceleration. Two, in those cases where an object is traveling horizontally, there are other vertical forces canceling gravity, such as a normal force, or some combination of normal and tension forces.

AP Schedule

Here are the schedule and support material for Waves and Oscillations
http://h1.ripway.com/DrCherdack/APUnit9OscWavessch11.doc


http://h1.ripway.com/DrCherdack/HmwrkonOscillsWaves2-08a.doc
http://h1.ripway.com/DrCherdack/Notes%20on%20Waves4-09.doc
http://h1.ripway.com/DrCherdack/unit9problemsheetr1.doc

http://h1.ripway.com/DrCherdack/unit9worksheet1r1RNC.doc
http://h1.ripway.com/DrCherdack/unit9worksheet2.doc

http://h1.ripway.com/DrCherdack/MaterialPropertiesandLongr1.doc
http://h1.ripway.com/DrCherdack/NotesonTransverseWaveSpeedR1.doc

AP Midyear review

Review assignments are due day of test. They will go from worth 4 homeworks of credit down to 2 if they are late.

Honors

Reports are overdue for all but four groups. You've lost 5 points off the top.

Your midyear review assignments are due the day of the test. They are worth four homeworks.
I received none from section 2 so far. They are now worth 2 assignments for you (section 2) instead of four if you turn them in by Thursday morning.

Honors Research Reports

Yes they are due tomorrow. No, your slideshows are not reports

AP and Honors

Remember to bring in your equations sheets

Honors Equations Sheets

Please add the following FG =GM1M2/r^2

Please fix the following v =Dx/Dt

a = w^2x for oscillator

Honors Review Corrections

#13 .d. a and v are negative
#27 should be -.46
#44 should be 400 J
# 61 last force is .324 not 3.24N

Honors Definitions and Equations

This should give you what you need. Let em know if you honestly think you need something else as far as this list goes.

http://h1.ripway.com/DrCherdack/midyr%20DefsEqns10-11.doc

Solutions to Number 85

Got through all but vectors. Left a couple of the first 85 unanswered, so I could get this thing posted


http://h1.ripway.com/DrCherdack/Midyrrev10-11hnrsR1sln-1.doc

Honors Review

The solution link from Monday (yesterday) will now get you the latest solutions, up to number 59. I'll try to finish earlier tomorrow

Honors Review

Problem 25 the final equation in the solution should have been Delta p not Delta m

AP Review

So far the one error I found in the solutions is for number 5, the first acceleration is -2m/s^2, but I am only up to question 14.

There will be some questions about oscillations on the exam so remember what we covered Monday. F=-kx, PE = 1/2 kx^2, omega(looks like a wavy w) = sqrt(k/m), vmax = omega A ( A is amplitude, maximum x) KE max = PE max = E total = 1/2 k A^2 = 1/2 Mass * omega^2* A^2 ; Etotal = (PE +KE) [not PEmax+KE max]at any point.

x= A cos(omega t), a=-kx/M, v = - omega A sin (omega t)

Honors Additional Material

Just in case you were looking for something to do. Here are some questions on the other part of electricity and magnetism you should be able to answer.

http://h1.ripway.com/DrCherdack/Midyrrev10-11hnrsAddl.doc

AP Solutions

I believe this link will get you the solutions. I've been working on the honors solutions. I'll get to check yours tomorrow.

http://h1.ripway.com/DrCherdack/APMidyrRev09-10%20sln.xls

Honors Solutions

Here is the first batch. I'll try to update it tonight.

http://h1.ripway.com/DrCherdack/Midyrrev10-11hnrsR1sln.doc

Labs

Do not forget all the labs to be turned in I posted last week.

Honors Section 3 turned in only 3 standing wave labs by Friday. The rest of you are down 5 points in your grade on this lab.

Re Tests

I am considering retests for AP fluids and thermo. If I can get to writing them at all, they'll be given next week.

HAC

I posted grades on the HAC. The only numbers that are relevant are the 1/13 figures for tests, labs, and homework. Nothing else counts. A few of you still need to make up tests, while the grade shown is only for tests you have taken. Lab grades try to approximate what you have and do not accurately reflect labs to be turned in. If you do labs regularly, I did not penalize you much for pending see me s, resubmits, etc.

All Students: Understanding Cause and Effect

Think about the physics of phenomena, don't blindly quote equations. You don't make someone run faster by reducing the time your stop watch shows for a race. It is quite the other way round.

I got a bunch of labs in that indicated that cause and effect are being inverted. Please reason correctly. For example, you make the acceleration greater by increasing the force on the object not the other way round. You make a wave go faster by increasing tension in rope, you don't increase the tension by making the wave go faster.

Group Reports

Every individual must submit her or his own group report for regular work. Only project reports ( honors only) are one per group. All I require is where, when ( date and time), and who, and one or two lines on subjects covered - not generic such as homework, must include the topic and Unit number.

Here is a reminder from the past.

Group reports

Reminder AP group reports once a week or no grade. Honors, once a unit or no grade.

Honors Standing Wave Lab

The majority of these were bad to awful, and most are being returned without grades. Here are some samples of why.

1) Purpose. Almost every lab is designed to confirm something we proposed as an hypothesis. You have been told this many times, most recently with your pendulum labs where you proved omega = sqrt(g/L) without most of you realizing you did it. In this case I spent more than a period trying to establish that, c (wave speed) of a transverse wave is given by c= sqrt(Ftension/(Mass per meter). We then discussed standing waves and established the hypothesis that a standing wave must contain n/2 wavelengths (i.e.n/2 lambdas), where n was any whole number. From this and the fact that a loop was half a wavelength we got number of loops = 2L/lambda

using lambda = cT = c/f we get number of loops (i.e. n loops)= 2L/(c/f) or number of loops =2 Lf/c which can be rewritten as c= 2Lf/number of loops. Substituting sqrt(Ftension/(mass per meter) for c and squaring both sides and then multiplying by (mu i.e. Mass/meter) gives you an expression for the Ftension required for n loops.

Proving the bold equations are correct are what the purpose of this lab was. Vague statements such as exploring relationships or determining relationships applicability are useless if the relationships you are trying to demonstrate are not stated. Most of you blindly quoted FT = 4L^2F^2(mu i.e. mass/meter)/ n loops with no explanation of where it came from. If you are going to use something like that, derive it and show you understand where it comes from and what it mean, or its just a formula that a child can plug numbers into and get answers.

2) Understanding of math is a rare commodity around here. Here are some typical bits of math from your labs:

"We proved 4L^2F^2(mass/meter, or mu))/ n loops is a correct equation." No equal sign, no indication at all of what it is supposed to equal, but still you were sure it was a correct equation.

"The speed = sqrt(FT/mu) therefore doubling the FT will increase c by 1/3."

"The speed is given by mu c^2 = FT/mu therefore doubling FT would quadruple c"

"Since lambda = cT increasing c by 1/3 increase lambda by 1/4"

By now the fact that you do not know that that the Sqrt( 2FT/mu) = sqrt(2) x (sqrt(FT/mu) is a scandal. Doubling FT alters c by a factor of the sqrt of 2 or 1.414. The new c = 1.414 x the old one and since lambda = cT = c/f, then if cnew is 1.414 c old then lambda new is 1.414 lambda old.

Graphing and slope is still a mystery to many of you. Graphs should be titled as vertical coordinate vs horizontal. Many of you labeled your lambdas as c and your c s as lambda. The slope of c vs lambda is f. You should have made this graph and your slope would have come out close to 60, the frequency supplied by the oscillator. Some of you graphed c calculated from c=sqrt(FT/mu) vs (sqrt(FT/mu) and came up with the not very surprising result that slope =1.

You were supposed to graph c calculated or ideal from c= sqrt(FT/mu) vs c measured from c = lambda (measured) x frequency known = (2Lstring /n loops) x 60. Then a slope = 1 would mean our equations was right.

Discussion sessions are not supposed to be just answers to questions. Just providing minimal answers to questions is the work of a child and will earn 20 points off in the future. At the very least the percent difference between ideal and measured should be discussed.

Conclusions should state concrete results, confirming or denying the validity of those identified in the Purpose while citing the evidence for your conclusion.

Silly words and thoughts continue to be common. One group told me that the number of half periods that pass from a wave passing through a node and returning to the node would have to be odd to keep the node moving. Nodes have no displacement and do not move. In a standing wave all nodes and antinodes maintain their locations. The string moves up and down at an antinode but the location of the antinode does not change. This why they are called standing waves NOT traveling waves. The number of half periods must even by the the way because the outgoing wave after passing through the node is reflected from a fixed end as an inverted wave and it if comes back to the node an even number of periods later it will be just in time to cancel the displacement caused by another outgoing (uninverted) wave; exactly what you need to have a node.

Fix these up and do your next labs as if you know why you are doing them and as if you know a little mathematics.

AP Review and Oscillation Homework

Here it is. Watch for some additional problems. Do first 11 problems for class Monday. Do 18 each night thereafter.

http://h1.ripway.com/DrCherdack/APImidyrRev09-10.doc

Assignment on Oscillations: Read Chapt 14 sections 1 through 4 Read notes on circular and harmonic motions

http://h1.ripway.com/DrCherdack/NotesonCircHarmonic2-09.doc

Do Chapt 14 probs 1,3,7, 17, 21

Lab Reports

Lab Reports

There are several of you who have labs missing or have had labs returned to you without grades other than the remarks see me, resubmit, etc. Also I have returned many labs with pretty low grades in the hope that you would correct them and resubmit these labs. All these must come in by Tuesday of next week or you will receive horrible grades on them. There may also be some instances where your grades are simply missing. Please straighten these out ASAP, but by Tuesday the latest.

Here is a list of the problem labs as of Tuesday: [sm means see me, rs means I am waiting for a resubmission, ng means a I need to see the lab to record a grade, ml means I have no indication the lab was turned in]

http://h1.ripway.com/DrCherdack/labs1-14.xls

Honors Review for Midyear exam

Here it is. We will go through it in order do 1-30 by Monday through 60 by Tuesday and try to finish up by Wednesday. We'll review in class but obviously we can't do them all so you need to tell me which ones we have to go over. Preferably by email the preceding evening.

http://h1.ripway.com/DrCherdack/Midyrrev10-11hnrsR1.doc

Honors Homework

For homework

1) look through your notes from the group presentations and my notes on waves, waves speeds, etc. and try to catch up on what you haven't done in the last week. Make sure you understand the electric force equation, it's just like gravity only k= 9E9 instead of G= .667E-10, and charge instead of mass.

2) Look over the subtopics I identified for your group and address as many as you can in your project presentation and report. However, just reciting them is not useful, creating understanding of where they come from and what they mean is. Keep in mind that doing a good job on just a few items is much better than just brushing on many.

Honors Project Groups

My apologies to the project groups whom I did not get to work with yesterday. I needed to address a few lab related issues. Then, with the midyear exams on the horizon, I thought it would be best to go over the last test again for the benefit of several students before getting to the projects. That cost us about another 30 minutes. Finally, the folks working on the NJ Physics Olympics have been putting lots of time with little attention from me, so when they asked for some time, I felt it was the right thing to give it to them.

As it was, one group and another student ended up staying and we were worked til about 5 PM, making some real progress. I congratulate them for their endurance. As for the rest of you, please don't let yesterday's experience discourage you. Also, recognize, as I think many of you are doing now, spending long hours while coming to grips with something hard to understand or achieving something difficult can lead to a very satisfying sense of accomplishment and even profound happiness.

Honors Assignment

We will still deal with waves this week so once again read the material posted November 1 on waves.

For Tuesday, do the standing waves worksheet posted November 1.

For Monday do the following:

Waves:

Find the wave speed for a transverse wave on a 5 m long clothes line with a mass of .2 kg ( for the whole 5 m) with a tension 160 N. How long does It take a wave to get from one end to the other?

A sound wave is traveling through a metal with a modulus of elasticity, Y, of 4 E11N/m^2 and a density, rho, (i.e. greek r), of 8,000 kg/m^3. What is the speed of the sound?

Answer the following questions from presentations. ( Numbers in [ ]represent section which must answer)

[ 2,3]What is the expression for the Coulomb force between charges. What is the force between a negative 1E-6 Coulomb charge and a negative 2E-6 Coulomb charge 2 m apart? Is it attractive or repulsive?

[2,3] Does the magnetic force occur to motionless charged particles or only moving ones?

[3] When ocean waves approach the shore do they speed up or slow down? Do they get taller? Does their frequency change?

[2,3] What causes normal waves (not tsunamis) in the ocean.

[2] What is the relationship between photon frequency and photon energy?

[2] Lasers require more electrons in ground state then normal or more electrons in excited state?

[2] Ocean wave energy is proportional to sqrt of height, height, square of height?

[3] How many types of quark are there? How many types of antiquark?

[3] How many quarks of what type are in each proton? each neutron?

[3] The force between quarks is related to their________

[3] are there quarks in leptons

[2] How many nodes are there on a guitar string for the fundamental (also called the first harmonic)?

[2] What does shortening the string do to the frequency?

Honors Assignment and projects

1) Work on the Satnding wave lab. Section 3 find the needed tension for 5,6, and 7 loops using mu = 9.17E-4, L=1.71, and f= 60 cycles/sec. Use the relationship between tension and n squared we ended up with in class today.

I asked you to repair the December Assignment. I meant to tell you to record your answers on the assignment so you could correct your errors without my returning what you handed in. Since I didn't do that and I still have them. Review the December assignment solutions, with corrections in prior posts, and see if you know can solve all the problems. If you can congratulations. If you can't then fix it so that you can. If you need help you know where to get it. If I don't here from you I will assume we do not need to address it in our pre midyear exam review.

2) Projects. Presentations so far have been mixed with several disappointments. Many do not reflect enough time invested or an attempt to understand rather than copy.

This is a course in concepts which ideally can be tested with quantitative predictions. What occurs, why it occurs, and an equation describing the relationships among quantities are what we are after here, not just a bunch of facts and formulas. Some things, like force between charges is a fact of the universe, but how that leads to magnetism can and should be explained. Why sound moves at a certain speed can also be explained and why wave speeds and lengths determine resonant frequencies can also be explained as can the energy in a wave.

Lasers are governed by quantitative behavior, etc.

I am hoping by next Friday every group will have done some real teaching and explaining.

Honors Homework

AP Homework

You really have to do the gas problems on the fluids review sheet from the fluids unit.

Honors Break solutions

PE for 2000 N/m spring should be .4J

Honors Solutions to Break Packet

Eagle eyed Emily Lopez noticed my error on the hanging mass cart problem. I wrote .84 instead of .804 m/s^2 for the acceleration and .804 should have been used to calculate the tensions.

Also see saw problem had no solution so here it is: d of 20 kg kid = 2.2X350N/200 N= 3.85 m

Honors Break solutions

Problem 5 b' efficiency = out/in

Honors

You should be able to answer the questions on the schedule using what we did today in 3rd period and what is on the notes on wave speed. Try your best

Honors December Packet

Here are the solutions:the methods are right but a few careless errors may have crept into the calculations

http://h1.ripway.com/DrCherdack/HnrDecember%202010Asgnsln.doc

Honors Sect2 and 3

Sect 2 The electrifying group with the magnetic personalities and the special ops present tomorrow; surfers present on Friday.

Do the following given L=1.71 m, mu = 9.17^10-4 kg/m find the tension needed to produce 7 loops i.e. n = 7 [use what we did today about c of a wvae on a string and relationship of tension, n, L and mu.]


Sect 3 will be electrified magnetized and enlightened tomorrow. Cosmology and Particles on Friday. Music can go on Monday( but we need to meet)

Honors Section 3

Print out first two pages of Lab on standing waves and bring to class tomorrow and Thursday

AP Section 5

We are a day behind so do your best to do the homework using notes and reading, but we'll go over it in class tomorrow.

AP problem Sheet N0.1

The beta should be an alpha. No matter what symbol you use, the coefficient of linear expansion for mercury is 1.8 x10^-4. Also the answer appears to be wrong. I believe it should be 13.5 cm. ( I probably used 10 Celcius as delta T instead of 30.)

AP Thermo

One more. Notes on Kinetic Molecular Theory ( KMT to its may friends). Reda them before we get to it in class.

http://h1.ripway.com/DrCherdack/NotesonKineticMoleculaR1.doc

AP Fluids

Too many of you sank. We'll have to go over the quiz tomorrow.

Labs!

Pendulum lab, purpose was to prove our derivation was correct, i.e. that omega = sqrt(g/L). This says omega does not depend on Mass or phi max.If omega doesn't depend on phi max (maximum angle from vertical) or Mass, period won't either. You should have calculated expected omega from above equation and compared it with 2 pi/Tmeasured and found percent error. Tmeasured is the period you measured with your stopwatch. Note T is one tenth the time t for ten cycles.

Archimedes lab. Prove FB is density of fluid x g x volume by using Vol = change in force from scale/(density x g) to find density of object and then compare that with known densities from values I gave you. If they match then your calculated volume is correct so the equation for FB is correct. Only then do you see if density x g x change in height x area = FB as it should. While the first part should give very accurate results the second part may have large errors since change in height can be hard to get correctly.

Many of you still confuse grams and kg etc. in your work. GET OVER IT.

Schedules for AP and Honors

Back to work guys. Actually, if you did your assignments you've never stopped working. To make up for that, no assignments for you folks for July this year. Don't thank me, I just can't help myself sometimes.

AP, somewhere in these problems there may be a couple of wrong answers. I'll try to catch them (for the eighth time - before you get to them)

http://h1.ripway.com/DrCherdack/APUnit8Thersched10-11.doc
http://h1.ripway.com/DrCherdack/Heat%20and%20Energy%20Conversionr2.doc

http://h1.ripway.com/DrCherdack/NotesonThermoR6.doc

http://h1.ripway.com/DrCherdack/Notes%20on%20Basic%20Gas%20Thermofor%20nmoles.doc
http://h1.ripway.com/DrCherdack/Notes%20on%20Steam%20Cycles.doc

Honors: A lot of stuff here. I think we will slow down for a week or so after the midyears. Give you a chance to catch your breath; but for now a three week push.

I don't expect you to do more than the simpler stuff on electricity and magnetism. Just get the basics. Also get a real feel for how light is emitted and what it is - waves and photons, but the problems will be simple.

We may do the standing wave lab as a class. We'll see how the timing looks, but in any case look it over by Tuesday or Thursday depending on your lab day.
http://h1.ripway.com/DrCherdack/HonorsUnit8Projects10-11.doc

http://h1.ripway.com/DrCherdack/Notes%20on%20Waves11-10.doc

http://h1.ripway.com/DrCherdack/NotesonTransverseWaveSpeedR1.doc

http://h1.ripway.com/DrCherdack/Notes%20on%20magneticsR8.doc

http://h1.ripway.com/DrCherdack/NotesElectrostatic3-08r1.doc

http://h1.ripway.com/DrCherdack/Lab%20on%20Standing%20Waves-09.doc