tag:blogger.com,1999:blog-5088860151651047897.comments2024-03-08T13:57:00.071-05:00Jacobs PhysicsGreg Jacobshttp://www.blogger.com/profile/03854009948036330746noreply@blogger.comBlogger1296125tag:blogger.com,1999:blog-5088860151651047897.post-8642892280461492892024-03-08T11:20:31.570-05:002024-03-08T11:20:31.570-05:00Anonymous, maybe an "example response," ...Anonymous, maybe an "example response," as has been provided on recent AP rubrics, would help? Here's a go.<br /><br />Consider N2L for the two block system. The net force on the system is the weight of the hanging object; that doesn't change, it's still 25 N. But the system mass is bigger. By a=F/m, the same F with bigger m means smaller system acceleration. That means the block on top speeds up by less over the distance to the table's edge, launching the projectile with a smaller speed than before. Finally, the ball is in the air for the same amount of time (because it's launched horizontally, so the vertical kinematics is identical). But horizontally, d=vt applies. Smaller v for the same t means a smaller d, which causes the ball to land closer to the table. Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-19204557688091855532024-03-08T11:13:25.046-05:002024-03-08T11:13:25.046-05:00Hey Greg, could you please go over this question? ...Hey Greg, could you please go over this question? I’m having some trouble with this questionAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-44692409805321866982024-03-05T13:54:48.195-05:002024-03-05T13:54:48.195-05:00Good 👍
Good 👍 <br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-57401255595491863642024-02-29T18:18:40.548-05:002024-02-29T18:18:40.548-05:00I've arranged AP Physics 2 so that the E&M...I've arranged AP Physics 2 so that the E&M portion of the year is a 4-unit mini-course that lasts from approximately December through February. The advantage of doing this is that static electricity experiments and demonstrations work so much better in the winter. I have no other good reason.Willnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-81515907370202710752023-12-21T00:10:53.726-05:002023-12-21T00:10:53.726-05:00This was very helpful, better than my college inst...This was very helpful, better than my college instructors teaching on this.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-63772507152576017112023-12-19T08:17:19.225-05:002023-12-19T08:17:19.225-05:00Completely anecdotal, of course, but I've foun...Completely anecdotal, of course, but I've found momentum bar charts more useful when momentum gets taught before energy. When I used to teach energy before momentum (different school, different year's schedule), I agree that momentum bar charts just confused things. I have no idea why that would be the case, and of course, your mileage may vary.Willnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-68344094852519681102023-12-18T13:01:56.792-05:002023-12-18T13:01:56.792-05:00Gilroy, many teachers do use momentum bar charts i...Gilroy, many teachers do use momentum bar charts in exactly the same way as energy bar charts - as a graphical way of representing the momentum of individual parts of a system, so that equations can be written from the representation. I've tried these, and I stopped using them. Momentum conservation is generally simple enough that even weak students have little trouble communicating with an annotated calculation; and then momentum vs. energy bar charts cause confusion. I'd prefer that students only have one type of bar chart to futz with. :-) But other people do use representations of momentum successfully!Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-82316962889136729082023-12-18T12:45:43.857-05:002023-12-18T12:45:43.857-05:00I'll admit, it's taken me a long time to c...I'll admit, it's taken me a long time to come around to energy bar graphs. Your analogize them to FBDs is a helpful frame for me -- I was hung up on how to use them in calculation, and neglected using them for organizing student thinking.<br /><br />Which leads to me to ask: Is there any corresponding thing for momentum? Any useful ideation tool?gilroy0https://www.blogger.com/profile/13586592076460054599noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-90563999884219894032023-12-17T21:26:39.663-05:002023-12-17T21:26:39.663-05:00I've been reluctant on bar charts for a few di...I've been reluctant on bar charts for a few different reasons. I do teach them, but I impart my cautions to the students as well. My biggest objection is that different books and sources format and use bar charts differently; the system isn't uniform, like scatterplot graphs more or less are, when it comes to what they must include and how things get labeled. AP Physics 1 exams have used a "stacked blocks" representation, whereas our textbook uses rectangles of equal width, whereas a different textbook makes both dimensions of the rectangle vary in each bar (i.e. if there are two forces doing 4 J of work on a system, but one is 1 N over 4 m and the other is 4 N over 1 m, one of these work bars will be 1 unit wide and 4 units tall, while the other one is 4 units wide and 1 unit tall)... And this is before we get to the lack of consistency between terms like "work done by friction" vs. "thermal energy" and so on. So even if students learn the bar charts, they will have to read the instructions next to the problem on how to construct them literally every single time they confront such a chart, because the process isn't consistent.<br /><br />It hasn't been all bad, though. In a larger, multi-part problem wherein graphs, equations, and bar charts are all demanded separately, it's a particularly good way to force students to check whether their multiple representations of a problem are consistent with each other.Willnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-82331508144846338192023-10-24T10:47:08.570-04:002023-10-24T10:47:08.570-04:00Love the lab idea. Some teachers may want to take ...Love the lab idea. Some teachers may want to take this further and have students solve for the spring constant of the plunger. This doesn't work well unless you know the spring is compressed about 1 cm when the plunger is fully extended. See this thread for details and a way for students to find the initial compression: https://twitter.com/kilroi22/status/1166054371114700800Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-78858375266193374532023-09-14T14:49:25.699-04:002023-09-14T14:49:25.699-04:00I used the simulation as a follow up to the motion...I used the simulation as a follow up to the motion graph activities. I showed the students the experimental setup and had them predict the motion graphs. I would then run the simulation for them to check.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-71565378863417406522023-08-25T15:10:57.865-04:002023-08-25T15:10:57.865-04:00No idea, Louie. AP1 already removed three units i...No idea, Louie. AP1 already removed three units in 2020 from the original course: electrostatics, circuits, and waves. Adding fluids doesn't even come close to bringing the course back to its original breadth. I don't think it's quite accurate to claim that material is added without removing anything. The subtraction and addition has simply been asynchronous. :-)Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-23634557464750976482023-08-25T15:04:46.379-04:002023-08-25T15:04:46.379-04:00Do you know if there will be a recommended amount ...Do you know if there will be a recommended amount of minutes per week of instruction after the changes take place? I'm asking since they are adding material to AP1, but not removing anything.Louienoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-67212431664899810092023-08-15T08:47:51.261-04:002023-08-15T08:47:51.261-04:00"Work hard, take care of one another, get bet..."Work hard, take care of one another, get better every day" – these are life's true goals! 🙌 Your students are lucky to learn from you.Couponsheavenhttps://www.couponsheaven.comnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-84558401934483785432023-08-02T21:57:04.928-04:002023-08-02T21:57:04.928-04:00Oops! Now I see it's 2025.. never mind!Oops! Now I see it's 2025.. never mind!Lisa Zaviehnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-83667509434277575772023-08-02T21:56:11.064-04:002023-08-02T21:56:11.064-04:00Any idea when the College Board will update AP Cla...Any idea when the College Board will update AP Classroom to include Fluids, as we're meant to teach it this school year?<br />Lisa Zaviehnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-49859495846663256022023-07-30T19:52:59.573-04:002023-07-30T19:52:59.573-04:00Over the past 13 years, I have taught most high sc...Over the past 13 years, I have taught most high school sciences (earth sci, bio, chem, ecology). The past two years, I started teaching AP Physics. I first came across Greg by watching him in college board's AP Physics 1 videos. I was immediately struck by his warm, welcoming approach to physics. The past two years, I had success in my classroom whenever I have tried his ideas and strategies from his videos, his blog, and 5 steps to a 5 review book. This coming year I will be teaching my first general level physics, so I knew that I just had to attend Greg's conceptual summer institute. And Greg turned out to be just as amazing in real life as he was in the videos. I was not disappointed. He laid out a plan that I can follow, from the very first activity on the first day of class to the culminating project of the year. Greg shared his labs, classwork sheets, HW, and assessments. Considering how many hours it would have taken me to find/adapt/create my own curriculum, the cost of this conceptual summer institute is an amazing deal. But Greg doesn't stop there. He makes a convincing argument for teaching conceptual physics to your students, regardless of whether you teach a general or advanced physics class. Greg shows how his approach fosters independence and confidence for students (and first time physics teachers!) And just as important, Greg shares how to approach student (and parent) complaints about grades, what to do when students bring a blank page to you asking for help starting a problem, and responding to poor behaviours. If you've read Greg's blog, you probably recognize some of these topics. But even if you've read every single one of his blog posts and sorted them by topic or unit for future reference (guilty...), attending Greg's class to hear how he weaves together his pedagogy, philosophy, and curriculum is absolutely worth it. Even if you don't teach physics, there's a lot in this class to think about adapting to other science classes. The only two things that could make this course even better would be if everyone could do the class live (instead of virtual) and if the class was a day or two longer. Greg expects his own students to work hard, get better every day, and take care of each other. As a student in his conceptual summer institute, I got to experience all three of those.Mark Mailhotnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-77629053500100947512023-07-12T15:31:31.794-04:002023-07-12T15:31:31.794-04:00Oh! I see this many years later. Answer is, I wo...Oh! I see this many years later. Answer is, I would recommend. Chris knows his business. I've not used the book myself, but it is well aligned with the P2 exam.Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-27666000620572517462023-07-11T10:03:39.166-04:002023-07-11T10:03:39.166-04:00Will, I encourage you to come to the reading. I p...Will, I encourage you to come to the reading. I personally love to talk about the AP Physics 1 rubrics - I've been leading their design and implementation since 2015. The fundamental design goal of a rubric is to consistently award credit for good physics, and to consistently avoid awarding credit for poor physics. Most of the P1 rubrics have been quite successful on this account. <br /><br />When you join us at the reading, you'll have the chance to see the elegance of how a rubric applies consistently and appropriately to hundreds of thousands of responses. And, you'll be able to talk directly to the people who design the rubrics. I think you'll find your concerns addressed appropriately - and that you don't have so many concerns once you see first-hand how the process works. Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-81908772395641259812023-07-11T00:23:55.784-04:002023-07-11T00:23:55.784-04:00Oh, I'm not concerned with the graders, per se...Oh, I'm not concerned with the graders, per se; physics teachers are very good in general at spotting actual knowledge vs. rote recitation. It's more about the grading rubric they're working with. And I know that's not the part we like to talk abut---we'd much rather talk physics knowledge. But it's been the achilles heel of the AP1 exam. The 2018 FRQ5 is a good example. The first part is at least 2 mathematical steps, but only earns 1 point. And the paragraph earns 6 points, all of which are instantly lost if the student doesn't recognize the inelastic collision. On 2023 FRQ1 the problem is different, only slightly; if a student says the underlying principle is conservation of energy but does not clarify the difference between "same energy" and "energy is conserved," they're in trouble.<br /><br />If the rubrics were qualitative--e.g. 5 points for a completely correct answer, instead of parsed out point by point for each learning objective met--then I'd have more confidence in the process, because it would be more about the student showing what they know and less about trying to "hit" every point.Willnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-82209235172273692262023-07-10T19:30:47.444-04:002023-07-10T19:30:47.444-04:00Will, the first two answers you quoted each earn f...Will, the first two answers you quoted each earn full credit. And I don't believe this question is in any way "splitting hairs" about language. Would we accept a student calling any old equal and opposite forces a N3L pair? It's the same thing. The question is expressly testing the misconception that I describe in the post.<br /><br />Now, if you're worried about pedantic grading, please don't! The AP exam is graded by physicists, not robots. A student who first explained that the total energy depends on the unchanged spring stretch, THEN explained that conservation of energy keeps the graph identical at each position, earns credit. They talked about conservation of energy correctly. But a student who says that the total energy is the same in the new case than the old case "by conservation of energy" is not demonstrating understanding of the situation. And a student who quotes the old saw that "energy can neither be created nor destroyed" without applying said saw correctly in context is not communicating physics understanding. Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-44205324530309836042023-07-10T19:07:37.975-04:002023-07-10T19:07:37.975-04:00My one li'l gripe about this problem is that t...My one li'l gripe about this problem is that the answer comes out a little too close to, "Because this here formula says so," for my liking; an answer along the lines of, "dropping the second block on top of the first doesn't change how stretched the spring was" or "doesn't change the amplitude of the oscillation" is a stronger causal argument for there being the same total energy in the system before and after the second block arrives. Alternately stated, that means there is "zero change in the system's total energy." Which, if you're going to split hairs about using the words "conservation" in an introductory physics course, is a wee bit pedantic. I was just happy if they didn't copy the 2018 paragraph answer and say "the collision slows it down because kinetic energy's lost in an inelastic collision." Or similar.Willnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-82084577911125900672023-07-10T12:21:06.139-04:002023-07-10T12:21:06.139-04:00Ryan, before I answer, I just want to point out to...Ryan, before I answer, I just want to point out to readers that the actual 2023 P1 question asked for a graph of KE vs. PE for the spring-cart system. No energy bar chart was necessary. Your question is really fascinating, but was NOT part of the AP Physics 1 exam in 2023!<br /><br />Okay, here's what I see. At the max extension, the spring-cart has 4 J of potential energy and no KE. At the equilibrium position, the spring-cart has 1 J of kinetic energy and no potential energy. <br /><br />The question that I suspect Ryan is really after is, how do we account in an energy bar chart for the remaining 3 J? Yes, they have become kinetic energy of the block, but the block is external to the system, and thus can't be included on the bar chart for the spring-cart. Nor can these 3 J be chalked up to internal energy - again, because the block is not part of the system, so nothing involving the block can be "internal."<br /><br />There must be an external force doing negative 3 J of work on the cart-spring system in order to reduce its mechanical energy from 4 J to 1 J. That conclusion comes straight from the energy bar chart and "bars + bars = bars", that is, conservation. But what is that force?<br /><br />While the cart and block move from maximum spring extension to equilibrium, they both speed up together. Consider a free body diagram of just the block on top of the cart. The cart exerts a (probably frictional) force in the direction of motion, causing the block's acceleration. By Newton's third law, the block also exerts a force on the cart opposite the direction of motion. <br /><br />And there you go. The cart experiences four forces. The normal force and the weight are perpendicular to the direction of motion, so do no work. The spring is part of the cart-spring system, so is not considered in the "external work" column in the energy bar chart. The force of the block on the cart is opposite the direction of motion, so does negative work. And since the block is not part of the cart-spring system, this work is represented in the "external work" column.<br /><br />TLDR: The bar chart for the cart-spring system looks like:<br /><br />* At maximum spring stretch: 4 bars potential energy, 0 bars kinetic energy.<br />* Work done by external forces: -3 bars, due to the force of the block on the cart.<br />* At equilibrium: 1 bar kinetic energy.<br />Greg Jacobshttps://www.blogger.com/profile/12121422726610824760noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-49790809035097917162023-07-10T09:16:09.859-04:002023-07-10T09:16:09.859-04:00Great points about using conservation laws correct...Great points about using conservation laws correctly, Greg. <br /><br />For part (cii), how would you draw an energy bar chart representing the system of only the cart and the spring when the block now has 3/4 of the spring's energy but it's not in the system?Ryan Martinhttps://www.blogger.com/profile/05563131371690680957noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-52473479491043698272023-06-27T07:20:51.989-04:002023-06-27T07:20:51.989-04:00I highly recommend this institute. I am new to te...I highly recommend this institute. I am new to teaching and taught AP Physics for the first time last year. I attended Greg's APSI and then followed up with this institute to help reinforce the methods, information, etc. Greg's institutes made so much difference for me in all levels of physics that I taught last year. Time with him is time well spent!!! Pat Lukernoreply@blogger.com