Everyone

Well, I was going to start this note with some remarks about some lab reports, but I thought it might be better to let that wait.

So instead:

I hope you have a very Happy New Year with lots of joy and success - especially when it comes to physics.

Everyone

1) The attendance today was very disappointing. It reflects an attitude toward our class that I am sorry to see. To those who did attend class, thanks. I hope you enjoyed and benefited from it.

2) Break Assignment. AP you already have yours.

Honors: Here it is. Counts as 4 homeworks. Present answers on clean sheets not the assignment. Show work for problems. Problems can count as a take home test for you if you declare it so. You can use notes, texts, and even help each other but you must understand what you did. I will question at least some of you and if I believe you just copied I will disallow the test for everyone.


http://h1.ripway.com/DrCherdack/December%20Assign.doc

3) Honors projects: Be prepared to present at least one forty minute class on your topic by January 3rd. A second presentation and written report covering all items in your outline will be required by January 11.

4) We raised about $430 for the Smile Train. Nice work everyone.

5) Enjoy your holidays, be kind to your friends and relations and do something good for strangers. See you next year.

Simple Harmonic Part 3 data

If your part 3 data was poor and led to ks much different from parts 1 and 2, use these data

Amplitude m Time of card through gate Velocity max m/s

.05_________ .103_________________ .1844

.1 __________.051__________________ .3725

.15________ .033 _____________________.5758

.2 __________.025 ____________________.76

.25 ___________.020 __________________.95

Physics Tee Shirts

Get your orders in tomorrow for the shirt of the decade - The Ridge Physics Tee shirt.

Check payable to Ridge Activities - Physics or cash.

Follow the link to see it in full color and print an order form. (You don't need the order form; any paper with your name, size and teacher's name will do)

http://h1.ripway.com/DrCherdack/PHYSICS%20TEE%20SHIRT.doc

Charity Jar

Today's donations were pretty thing except for continued outstanding generosity from Joey. Let's dig in and make a real difference in some kids life.

AP Break Assignment

Your Break Assignment is in the out folders. It comprises three parts : a set of ten problems ( if I counted correctly - don't laugh, it could happen) -do not write on this; a graph for completing question1 - you can write on this; a set of equations for your use throughout the rest of the course.

The assignment will count as five homeworks. Problems are to be solved on clean sheets with all work shown. Booklets are to be kept clean and unmarked.

All Classes Units

I found lots of errors in choosing units, especially in the Simple Harmonics Lab (AP you'll be doing this soon enough).
The dimensions of a quantity are easily found. For example k is used in

Force (N) = k* displacement (m). Since k* (m) = N k must have units of (N/m).

Newtons are also (kg m/s^2) so k also has the units of (kg/s^2)

A graph of period squared vs Mass has a slope with units of time squared/mass or (s^2/kg)

A graph of v vs Amplitude must have a slope of (m/s)/(m) = (/s).

In another lab I asked what the units of energy /mass were, these are ( kg m^2/s^2)/kg =m^2/s^2

Pendulum Lab

We spent a precious period seeing that pendulum motion has an acceleration proportional to the displacement from equilibrium, so the motion should be harmonic.,and for a pendulum omega squared =g/L or omega =. Your lab was supposed to demonstrate that T ( which you measured) should equal 2 pi/sqrt(g/L) , your expected value of T based on our hypothesis about omega = restoring acceleration/displacement.

Power Lab

I am still getting in labs that miss the main point, viz. that power increases with decreasing time to perform the work. While the KE did increase with reduced time as speed has to increase, the real major effect comes from the change in PE, which is much larger than the KE, comes about in a shorter time.

Tis the Season

Remember the collection jar in 506 and always think of helping others.

Archimedes Lab

I am concerned that many of you will soon, if not already, confuse the reading of the scale with the object submerged with the mass of the beaker+ mass water + mass of object. This is NOT the case.

the reading of the scale with the object submerged IS the mass of the beaker+ mass water + the force of the object on the water. This last quantity, the force of the object on the water, is the buoyant force.(except it's down where Fb is up)

Labs

1) The Rotational and Translational KE lab asked two questions that received a large number of incorrect answers.

1) Would the velocity be affected if the mass of the ball changed. The correct answer is no, because both the KE and PE are proportional to the mass so that increasing the mass would increase the PE converted to KE sufficiently to keep v the same, or in equations

.7M vfinal^2 = Mg h initial

3) What would be the velocity if the ball just slid without friction instead of rolled. Since the final KE would still equal the initial PE we have PEi =.7Mvroll^2 = 0.5Mvslide^2

so vslide^2 = .7/.5 vroll^2 or

vslide = sqrt(.7/.5) vroll

Honors Test

Section 2 please return your tests. I need to correct one of he answers.

Honors Projects

Your assignment for the tonight and the weekend is to produce a detailed outline of what you will present to the class and in a report. The outline must include addressing the subtopics I indicated for your area. One outline per group.

Labs will be a real plus, demos are also important. Contact me immediately with any needs in this regard.

It should be annotated with sources.

In must be in on Monday. It will be graded.

AP Problem Sheet for Fluids

Here it is, no excuse for not doing it now.

http://h1.ripway.com/DrCherdack/Unit%207%20AP%20Prob%20Sh-06R2.doc

Governor's Schools Science and Engineering

Governor's schools are opportunities to study science or engineering at the college level this summer. A good way to learn and also looks good on applications, for those few of you thinking of going to college.

Read about them on Miss Donlevie's website.

Food Drive last Day

We need a really big push for this. We are still about 20 bags short of what we should be doing.

AP Section 5

Please return your tests to me. I made an error in my answer sheet and you may be getting a few more points, and we both know you can use them.

Tee Shirts

Due to popular demand ( Irwin Popular demanded it) tee shirt orders will be accepted until Thursday 12/16 This probably kills Christmas delivery but they will make great Valentines gifts (don't quote me).

Food Drive

You've got the weekend to purchase food and bring it in on Monday. We are still way short of one bag per person and the drive ends Wednesday

Honors Schedule

Here is the schedule for the remainder of harmonic oscillations. Note the quiz on Thursday.



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


http://h1.ripway.com/DrCherdack/HonUnit7sched10-11.doc

Lab Cleanup

Lab cleanups have been nearly nonexistent. The lack of care and courtesy shown by you has been appalling. For example, I have just put away all but one of the springs from the harmonics lab. Stopwatches are all over the room. Cardboard flags and weight sets are also all over the place. This is typical. Do not allow this to happen again. W hen you finish a lab you ask if it should be put away and do what you are told.

Rotational KE Lab

Here is the link:

http://h1.ripway.com/DrCherdack/Rotating%20and%20trans%20KE%20lab.doc

Honors Schedule

Here is your assignment for tonight. I would have had a full blown schedule for you but the Rotational Motion Group from Honors 2 took up all my time so here is tonight's assignment for now.

Work on Harmonic Motion Lab
Fix whatever you did wrong on Rev sheet prob 4 and 5 and spread sheet on Harmonic Motion.

AP Sect 5

When you left the room today there were two text books laying on the floor along with two markers and a white board. This is an indication of poor manners and lack of consideration. Please do not let this sort of thing happen again. I would like to continue thinking I am fortunate enough to have fine young people as students.

AP Fluids Schedule

Here is your schedule for fluids. Note that the same physics principles continue to apply to fluids. Work still is the transfer of energy, momentum is still conserved or changed by F from external sources x Dt, and Win = D PE + D KE + losses. In some very real sense all that has changed is that we are dealing with a volume of material instead of individual objects. Fg is still -Mg on earth. Do not be intimated by the new vocabulary we will use to discuss the physics of collections of particles instead of single objects.

Make sure you read and understand the lab (see link below) before we actually do it.

http://h1.ripway.com/DrCherdack/APUnit7Fluidsched-10-11.doc


http://h1.ripway.com/DrCherdack/Notes%20on%20FluidDynamic%203-10.doc


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


http://h1.ripway.com/DrCherdack/Archimedes%20Lab%2012-08.doc

Honors Corrections

Sorry, there were a couple of typos in recent posts.

KE is Mv^2/2 as you all know and

a = -omega^2 x

Use these corrected equations in the spread sheet and work sheet assignments due yesterday and today.

Tee Shirts, Food Drive

Just do it.

Honors

Honors 3 will not have the computers tomorrow and Friday. Sorry, you'll have to listen to me. We'll do the simple Harmonic Lab. You should have a copy of the 09 version. I posted the '10 version earlier this week. Look it over.


All groups try you best to complete last night's assignment as well as tonight's. Remember that omega =sqrt of (k/M) v =-omega A sin(omega t) and a = -omega^2 x. PE = kx^2/2 create a column next to KE and see if KE + PE is constant.

Tee Shirts

Think how confident you'll feel starting the new year wearing your Ridge Physics T shirt. Orders are due Thursday.

Honors Assignment

Make sure you did the examples posted over the weekend and then try this worksheet. Section2 should be able to do this. Section 3 here is the information you need:

Theta = omega t use this in all the circular equations for x position, vx, and ax, and they are now the right equations for an oscillator, provided omega = sqrt(k/m) and the radius = A = xmax ( maximum displacement from the equilibrium point x=0).



http://h1.ripway.com/DrCherdack/oscprobA4-09.xls

To find the KE just use mass times v^2/2 and for PE use kx^2/2

AP Power in Rotation

Problem 3 in the Rotational Energy WS asked you to find power using torque x omega at 15 and 30 seconds. Try finding the power from the rate of change of rotational KE , i.e. the rate of change of I omega^/2.

To do this remember I is constant so we have I/2 (omegaf^2- omegai^2)/delta t. Approximate omegaf as omegai + alpha delta t. Carry out the (omegai + alpha delta t)^2. Then cancel terms where appropriate and divide the numerator through by delta t . Then let delta t get infinitesimally small so any term with a delta t goes to zero. Use omega at 15 and see if the power matches the one found from torque x omega.

Food Drive

If every student brought in 1 full bag of groceries it would represent a small expenditure per student but a magnificent food drive. Right now 506 has totaled about 12 bags . Figuring all of honors 2 plus all those who are not doing anything in their first period classes we should end up at near 40 bags. Let's get a move on. Place a bag of groceries next to your book bag tonight. Mark a big 506 on it.

All Students - Homework

Put the DUE DATE as given in the schedule and/or blog as well as your name on each assignment. Otherwise you will not get the credit your wonderful efforts deserve.

Simple Harmonic Motion Lab

Here is the link to the updated version. Look it over and see if there are any differences. I know about the fact that it specifies 500g for Parts 3 and 4.

http://h1.ripway.com/DrCherdack/Simple%20Harmonic%20Motion%20Lab-10.doc

AP Assignment

Finish Energy and efficiency you started in class and then do this


http://h1.ripway.com/DrCherdack/Rotational%20Energy%20Worksheet.doc

Honors Schedule

Better late than ...oh. never mind

http://h1.ripway.com/DrCherdack/HonorsUnit6Rot2sch10-11.doc

These are tough but do 4 and 5 on Wednesday [and Thursday only if we don't get to energy on Wednesday.]
http://h1.ripway.com/DrCherdack/RevProbRotandHarmR2.doc

All

1) Tee shirts: bring cash or check but bring money and order sheet. Buy several you can where one each day of the week

2) Food Drive - need I say more. Well I will any way. We are not among the top two classrooms yet. Let's fix that!!

Honors new stuff

1) Make sure you read the previous post and do the reading and assignment

2) Be prepared to do research Thursday and Friday, Look at the list of items I supplied and make sure you can discuss them intelligently by a week from this Thursday.

3) We are moving into oscillations starting Tuesday. We will begin with a comparison of something bouncing back and forth on a spring and something going in a circle. Make sure you read the following by Monday night.

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

Here are some questions to answer by Wednesday

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

We will also look at conservation of energy in an oscillator. Thus make sure you are familiar with KE and the PE of a spring with a mass attached( k DeltaL^2/2)

4) Here is the lab we will do this week. Read it over by lab day.

http://h1.ripway.com/DrCherdack/Simple%20Harmonic%20Motion%20Lab-09.doc

Honors On Rotational Motion

Here are up to date notes on torque and angular momentum.

http://h1.ripway.com/DrCherdack/NotesonTorquerev12-5-10.doc

They cover some of what the Rotational Motion Group will present tomorrow in period 2 and I will present in period 7. Read them so you will be able to follow it.

For tomorrow answer the following questions based on all you have ( or should have) learned about rotational motion so far.

A solid disk of radius R =50 cm and mass 10 kg is at rest. A tangential force of 10 N is applied at 25 cm from the center of this disk. Note that for a solid disk I = MR^2/2. Also note that 50 cm does not equal 50 m. Find the following:

aplha ( rotational acceleration)

atangential of a point at the edge of the disk i.e. r =50 cm.

After 20 seconds what is:

omega

vtan at the edge

the KE of the disk

the L of the disk

the work done by the torque

the distance traveled by a point on the edge.

the acentripetal of a point on the edge.

Four Words

Food Drive

Tee Shirts

AP Power and Eficiency

You should finish the Power and Efficiency worksheet tonight.

Here it is for those who lost it.
Power and Efficiency Worksheet

Power equals the rate at which work is done or the rate at which energy is transferred from one system or object to another. it is measured in Watts (W)

Power = Work/Dt.

Power x Dt = energy

Power provides an indication of how rapidly work can be done. If you must raise a large mass quickly, you need a more powerful motor to raise it then you would need if you needed to raise it slowly.

Efficiency is the ratio of useful work obtained to the work or energy put in to the effort. This is also described as work out /work in

eff = Woutput/Winput one symbol used for efficiency is , the Greek letter eta.

Examples: a) What is the power required to lift a 1kg mass 15 m in 5 sec?


b) The motor receives 45 W from the power company. What is the efficiency of the motor and the lifting machine? Since the useful power obtained is 30 W and the input power is 45 W, the efficiency is 30/45 = 0.67 or 67%.

1) What power is required to lift 20 kg 25 m in 30 sec?

2) How much power is required to change the kinetic energy of a car by 1,200,00J in 3 seconds? (ignore friction, etc.)

3) How much power is required to accelerate a 1400 kg car from 15 m/s to
20 m/s in 3 seconds?

4) If the engine actually delivers a power of 120,000 W during this time and the increase in kinetic energy is considered the only useful work, what is the efficiency of the process?

5) A light bulb receives 60 W of power for 20 minutes. How many J of energy did it receive?

AP Collision derivation

Read this for tomorrow

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

Honors assignment

Do the following use torque = alpha I and the kinematic equations supplied earlier

A torque of 40 Nm is applied to a wheel at rest with an I of 3. What is alpha? What is omega after 3 seconds, 20 seconds;what is delta theta after 3 seconds, 20 seconds?

Using I omega squared/2 = KE rotational, what is the KE after 3 seconds and 20 seconds?

If torque equals work per radian traveled what is the work done in 3 seconds, 20 seconds? (Please, please, please know that delta theta is radians traveled in this application). Does this match the change in KE?