Physics 8 — Wednesday, August 26, 2015Welcome!

I Web page: http://positron.hep.upenn.edu/physics8

I Note that this course meets every other year! So Phys 008will next be offered in fall 2017.

I Physics 8 covers a pretty similar set of topics to otherintroductory college physics courses, such as Phys 101 (forpremeds), Phys 150 (for engineers), Phys 170 (for physicsmajors), etc. What makes it Physics for Architects?

I Most (2/3?) of you are ARCH students. Having your owncourse lets us tailor it to your interests and your backgrounds.

I Once we’ve covered the basics, we’ll spend a few weeksapplying what we’ve learned to study topics related toarchitectural structures: trusses, cables, beams, etc.

I Most of you are “visual learners.” Lots of in-classdemonstrations make the physics concepts memorable.

I You’re used to working together. So I encourage a lot ofcooperation and discussion in this course.

I I know how much time you spend on your studio projects. So Ido my best to keep this course low-stress for you.

Instructor: Bill Ashmanskas (me)

ashmansk@hep.upenn.edu

office: DRL 1W15, tel. 215-746-8210mobile: (write on board)

You can stop in any time my door isopen, or else email to set up a time.I’m normally at Penn from 9am–6pm.But my door will probably be closedM,W,F mornings, while I’m hurrying toprepare for class.

I teach physics & electronics here in the Physics Dept., and Idesign electronics for medical imaging in the Radiology Dept.

Course format

I I want to preserve as much classroom time as possible for youto discuss physics with your neighbors (e.g. predicting whatshould happen in demonstrations or in hypotheticalsituations), for us to try working through example problemstogether, and for us to review the ideas that you tell me youfind most difficult. So I try to minimize “lecturing.”

I Instead, we’ll typically have textbook reading due on Mondaysand Wednesdays. That lets us make better use of the classtime, because topics we discuss in class will already have beenintroduced to you in the reading.

I Most Fridays (starting 9/4), you’ll have a set of homeworkproblems to turn in. The only way really to learn physics is bydoing it. Most of what you gain from this course will be theresult of the time you invest in working through these practiceproblems — both at home and in class.

I This problem-solving should be fun and cooperative. We’rehere to help you — and your classmates are too.

I Starting next week, I’ll be in DRL 3W2 Thursdays6pm–8:30pm (or later if need be), to help you with problemsyou find difficult, or to let you double-check your results.(This is just after studio ends.)

I Camilla will host a similar session on Wednesdays: do youprefer (A) 4–6pm, (B) 5–7pm, (C) 8–10pm?

I These HW sessions are totally optional for you. I really enjoythem, as they are a fun way for us to work with you and to getto know who you are. Past students have found them helpful.

Teaching Assistant:

Camilla Schneier(college physics major)

sccami@sas.upenn.edu

Camilla will grade your weeklyhomework and will run theWednesday HW study session.(I’ll do Thursdays.)

Why are you here?I If you’re here just to take a college physics course, that’s

great. Here are my terms: You put in a consistent 10 hourseach week (total) on reading, homework, and in-class work;and I’ll do my best to make Physics 8 fun, informative, andstress-free for you.

I You may be here because Physics 8/9 is required for theIntensive Major program in architecture at Penn.

I . . . or because eventually, to be certified as a practicingarchitect, you will take exams covering structures, heating/cooling systems, plumbing, electrical systems, acoustics, etc.

I . . . or because making a detailed energy model of a buildingdepends on the physics of heat and light.

I But I think more generally you’re here because many of youwill someday design things that will exist, will be seen, andwill function in the physical world that surrounds us. A betterunderstanding of the physical world will make you a betterdesigner. And if you work with engineers on designs, you canask better questions if you all speak the same language.

(why you’re here . . .)

I So in the fall term we’ll focus on mechanics, which shouldprepare you well for the Structures course that many of youwill take as seniors.

I While learning (or re-learning) Newton’s laws of motion, you’llexercise the mathematical side of your brain.

I By the way, how many of you took a physics course in highschool? (A) Yes, (B) No.

I How many of you studied enough calculus to be comfortablewith the idea of a derivative (e.g. dx/dt) as a “rate ofchange?” (A) Yes, (B) No.

I Prof. Farley, who teaches Structures (ARCH 435/436) here,tells me that he wants students to enter his course with asolid understanding of forces, torques, vectors, andtrigonometry. A key goal of Physics 8 is to leave you wellprepared for his course.

I For a long time, architects have been designing structures tospan spaces. Is physics relevant to this pursuit?

I Let’s make a model of a bridge. (Physics often uses modelsto simplify problems.)

I The two supports are spring scales that read kilograms. The5 kg block represents a truck crossing the bridge.

I If I put the “truck” in the middle of the bridge, what will eachscale read?

I What if the truck is off-center, i.e. somewhat closer to theright side? What can we say about the two scale readings?

I What if the truck is all the way on the left or right side?

I These three points might inspire us to make a hypotheticalmodel for what the scales read for other positions of thetruck. We might draw a graph to represent that model.

I What if the truck is 1/3 of the way across, i.e. 2x fartherfrom the right side than it is from the left side? Can you andyour neighbor predict what the left and right scales will read?

I The two supports are spring scales that read kilograms. The5 kg block represents a truck crossing the bridge.

I If I put the “truck” in the middle of the bridge, what will eachscale read?

I What if the truck is off-center, i.e. somewhat closer to theright side? What can we say about the two scale readings?

I What if the truck is all the way on the left or right side?

I These three points might inspire us to make a hypotheticalmodel for what the scales read for other positions of thetruck. We might draw a graph to represent that model.

I What if the truck is 1/3 of the way across, i.e. 2x fartherfrom the right side than it is from the left side? Can you andyour neighbor predict what the left and right scales will read?

I The two supports are spring scales that read kilograms. The5 kg block represents a truck crossing the bridge.

I If I put the “truck” in the middle of the bridge, what will eachscale read?

I What if the truck is off-center, i.e. somewhat closer to theright side? What can we say about the two scale readings?

I What if the truck is all the way on the left or right side?

I These three points might inspire us to make a hypotheticalmodel for what the scales read for other positions of thetruck. We might draw a graph to represent that model.

I What if the truck is 1/3 of the way across, i.e. 2x fartherfrom the right side than it is from the left side? Can you andyour neighbor predict what the left and right scales will read?

I The two supports are spring scales that read kilograms. The5 kg block represents a truck crossing the bridge.

I If I put the “truck” in the middle of the bridge, what will eachscale read?

I What if the truck is off-center, i.e. somewhat closer to theright side? What can we say about the two scale readings?

I What if the truck is all the way on the left or right side?

I These three points might inspire us to make a hypotheticalmodel for what the scales read for other positions of thetruck. We might draw a graph to represent that model.

I What if the truck is 1/3 of the way across, i.e. 2x fartherfrom the right side than it is from the left side? Can you andyour neighbor predict what the left and right scales will read?

I The two supports are spring scales that read kilograms. The5 kg block represents a truck crossing the bridge.

I If I put the “truck” in the middle of the bridge, what will eachscale read?

I What if the truck is off-center, i.e. somewhat closer to theright side? What can we say about the two scale readings?

I What if the truck is all the way on the left or right side?

I These three points might inspire us to make a hypotheticalmodel for what the scales read for other positions of thetruck. We might draw a graph to represent that model.

I What if the truck is 1/3 of the way across, i.e. 2x fartherfrom the right side than it is from the left side? Can you andyour neighbor predict what the left and right scales will read?

By the way, these two scales report values in kilograms. What doesa spring-based scale (like this one) really measure, anyway?

(A) mass

(B) weight

(C) inertia

(D) What’s the difference?

I All materials deform (change shape) when you push or pull onthem. In November, we’ll study how the beams (or joists)beneath a floor bend in response to the “load” (the downwardpush) imposed by e.g. heavy furniture in the middle of thefloor. (Illustrate with ruler.)

I The scale measures how far an internal metal spring bends inresponse to an object’s pushing down on the scale’s platform.

I Usually(*) that downward push exerted by the object on thescale is equal to the downward pull that Earth’s gravity exertson the object. We call that downward pull of gravity theobject’s weight. Weight is usually measured in Newtons (aunit of force), while mass is usually measured in kilograms.

I (*) Assuming that the object and scale are not accelerating.

I But weight is proportional to mass. The constant ofproportionality is smaller e.g. on the Moon than it is on Earth.

I By the way, inertia is the same thing as mass. It measures anobject’s tendency to resist being accelerated.

I After a few weeks, this vocabulary will feel much more familar.

By the way, how is it possible that the two scales read zero when Iremove the “truck” from the bridge?

(A) The plank that forms the bridge deck is extremely lightweightin comparison to the “truck.”

(B) I used the “tare” feature of the scales to zero out the weightof the plank.

What do you expect the scales to read if instead of putting my5 kg “truck” in the middle of the bridge, I put this hollow cubethere, filled with water?

You and your neighbor can probably figure out how to answer this.

And what if instead of filling that little cube with water, we insteadfilled a roughly-cubic milk crate with water? Maybe we can find away to estimate what the scales should read then.

I If we neglect the weight of the plank itself, then there arethree things pushing or pulling on the plank.

I We’ll see, a few weeks from now, that these pushes and pullsare called “forces.”

I If we don’t neglect the weight of the plank, then there’s onemore pull: that of Earth’s gravity on the plank itself.

I One job of an architect is to find ingenious ways to appear todefy gravity. To do that, you’ll often work out all of the forcesexerted on a given piece of a structure, and make sure thatthe given materials are capable of supporting these forces.

I I have another example that we’ll look quickly at now, for fun,then come back and look at more carefully after we’ve studiedforces. It will be a few weeks before we get to forces.

Class meeting format . . .

I Spend a moment thinking of something that you are good at:something you do well enough that you really enjoy the timeyou spend working on it.

I Now turn to your neighbor and share your ideas on thesethings you’re really good at.

I Ask your neighbor how he or she learned that favorite skill.

Class meeting format . . .

I Spend a moment thinking of something that you are good at:something you do well enough that you really enjoy the timeyou spend working on it.

I Now turn to your neighbor and share your ideas on thesethings you’re really good at.

I Ask your neighbor how he or she learned that favorite skill.

Class meeting format . . .

I Spend a moment thinking of something that you are good at:something you do well enough that you really enjoy the timeyou spend working on it.

I Now turn to your neighbor and share your ideas on thesethings you’re really good at.

I Ask your neighbor how he or she learned that favorite skill.

Class meeting format . . .

I Ask your neighbor how he or she learned that favorite skill.I How many of you said . . .

(A) By doing it / practicing?(B) By working with other people who share that interest?(C) By reading?(D) By asking questions after trying it yourself?(E) . . . other methods? . . .

I How many of you learned to do what you do best byListening to lectures?

Class meeting format . . .

I Ask your neighbor how he or she learned that favorite skill.I How many of you said . . .

(A) By doing it / practicing?(B) By working with other people who share that interest?(C) By reading?(D) By asking questions after trying it yourself?(E) . . . other methods? . . .

I How many of you learned to do what you do best byListening to lectures?

Class meeting format . . .

I I want you to learn as much as possible from the time wespend together in class.

I So I plan to make the class meetings as interactive aspossible, so that you are actively thinking about, discussing,and doing physics during class time, rather than passivelywatching me write equations on the blackboard.

I So normally I won’t “lecture” very much. Instead, you’ll doreading the night before and come to class prepared. In class,I’ll summarize the key ideas, and we’ll spend much of the hourworking on them together.

I As with a coach, a trainer, a piano teacher, etc., I’ll provide asmuch guidance as I can, but I can’t do the learning for you.

I Now let’s look at the course web page:http://positron.hep.upenn.edu/physics8

Online response formsAfter skimming Chapter 1 and reading Chapter 2, go tohttp://positron.hep.upenn.edu/wja/jitt/

Click “sign in.” Enter ID number. Click “email new PIN.”

Click “sign in.” Enter ID number. Click “email new PIN.”

Your PIN should arrive by email.

Now log in. If you click “remember on this computer,” then youdon’t have to bother logging back in next time.

You should see yourself signed in now. Click on today’s assignment.

Fill out the form and then click “submit.”

Fill out the form and then click “submit.”

This should generate an email to me, CC to you. If you have anytrouble, just email your answers to ashmansk@hep.upenn.edu

I do this so that the reading-response emails are automaticallyformatted in a way that is easy for me to process and search.

Physics 8 — Wednesday, August 26, 2015

I Course web page is athttp://positron.hep.upenn.edu/physics8

I PDFs of textbook chapters for the first few readingassignments are on Canvas, in case you don’t have your bookyet https://canvas.upenn.edu/courses/1295130/files

I Skim Chapter 1 as soon as you can, e.g. by the weekend.

I Read Chapter 2 before Friday’s class.

I Remember to fill out online response forms for both readingassignments athttp://positron.hep.upenn.edu/wja/jitt

I PDFs of these slides and other handouts can be found athttp://positron.hep.upenn.edu/physics8/files