General College Physics

Wisconsin Lutheran High School

Week 9

Reading: PSE Chap 6, Circular motion and other applications of Newton's laws

Topics: circular motion and newtons' laws

Lab:

Homework Problems:

Pulley on a platform: Solution. A man stands on a platform that has a pulley rigidly attached to its top surface. A rope is threaded under the pulley. One end of the rope is attached securely to the ceiling; the other end is held firmly by the man standing on the platform. By pulling up on the pulley, the man can cause the platform to rise.

Draw a free body diagram for the platform (mass M = 100 kg). Draw a separate free body diagram for the man (mass m=150 kg).
What must be the tension in the rope so that the platform is suspended in the air without falling or rising.
What must be the tension in the rope so that the platform rises at a constant velocity of 10 cm/second.
What must be the tension in the rope so that the platform rises at a constant acceleration of 10 cm/second squared.

The effect of buoyancy on a falling body: Solution. A pure indium ball having a diameter d = 1 cm is suspended from a tiny thread in a vacuum chamber.

What is the tension in the string? Hint: look up the density of indium (a soft metal).
If the ball is isuspended in a vat of liquid gallium (instead of a vacuum), what is the tension in the string? Hint: look up the density of gallium.
If the thread is now snipped, what is the acceleration of the indium ball as it falls through the liquid gallium? Ignore drag (but not buoyancy) for now.

The effect of drag on a falling body: Solution. In reality, drag reduces the acceleration of a falling body because it exerts a force opposite the direction of motion of the falling body. In the previous problem, as the indium ball accelerates, the drag force exerted by the liquid gallium increases until the sum of the drag and buoyancy balance the ball's weight. At this time, the ball achieves so-called "terminal velocity."

What is the terminal velocity of the ball? Hint: at terminal velocity, the acceleration is zero. Let's assume that the flow around the ball is turbulent, so that the drag force is given by D = 1/2 * (fluid density) * (cross sectional area of sphere) * (drag coefficient of sphere) * v^2. The drag coefficient of a sphere is approximately 1.
Now: repeat this problem for indium ball if it is submerged in liquid mercury (instead of liquid gallium). In particular: what is its terminal velocity? Does the indium ball ascend or descend?

Midterm: Monday Oct. 17

General College Physics

Return to course website.

Course syllabus

Physics: The world around us is in a state of constant change: the sun and moon rise and set, waves crash, mists rise, rain falls, fires burn, rocks form, and mountains crumble. Amidst all of these changes, there are certain patterns; there is a discernible order. In other words: the stars, the seas, the clouds, the rocks, and the earth itself each seem to have a particular nature. Physics is the careful study of the natures of things. In fact, the word physics literally means "natures" in the Greek language.

Course overview: General College Physics is a year-long introductory course for advanced (typically junior or senior level) students at Wisconsin Lutheran High School who want to better understand the natures of the things we see around us. It is a dual-credit course offered at Wisconsin Lutheran High School in collaboration with Wisconsin Lutheran College. For a detailed overview of the topics we will be covering, refer to the course website (www.greatphysics.com) and the tentative calendar on the following page. Emphasis on theoretical topics, careful thinking, laboratory experiments, and problem solving makes this course challenging. My aim is to help you succeed in this course, and to have fun while learning physics. So please do not hesitate to contact me with any problems you may run into this semester!

Advanced Placement credit: While this is not designated as an AP course, students students have successfully taken the AP Physics test at the end of the year for college credit.

Course textbook: The course will be organized around a book: the Pocket Guide to accompany Physics for Scientists and Engineers (4th edition) by Serway. (I’ll call this PSE for short.) I would highly recommend obtaining a copy of this book. It is inexpensive, compact, and well-written. It will make a very handy addition to your home science library. If you don't want to buy it, I will have copies to loan out for the semester.

Course time and location: The course meets every day (Monday through Friday) during the academic year from 2:16 until 3 pm in WLHS 223—in the science wing on the first floor of WLHS. On late start days (such as Wednesdays) the course begins at 2:24.

Professor: Dr. Kuehn from Wisconsin Lutheran College (WLC) is the professor for this course. Contact info: kerry.kuehn[at]wlhs.org

Teaching Assistant contact info: The Wednesday course sections (beginning in September) will be overseen by two teaching assistants. Alyssa Ebeling and Zeke Micheel are upper-level physics majors from Wisconsin Lutheran College. Here is their contact info: alyssa.ebeling[at]wlc.edu, ezekiel.micheel[at]wlc.edu

Course websites: In addition to the course information provided through WLHS’s OnCampus system, we will be also using a website I’ve designed for this course: www.greatphysics.com/WLHS1/

Homework exercises: I will assign weekly homework problems. These are designed to deepen your understanding of lecture material and to prepare you for the quizzes and tests. I do not intend to grade your homework solutions; I will merely give you credit for handing in your best attempt by the due date. Please refer to the late work policy for more details.

Laboratory exercises: Some of our weekly assignments will include laboratory work. Labs will typically take up at least two class periods. Your laboratory notebook pages must be submitted by the assigned due date. More details about the required format and expectations will be discussed before the first laboratory period. You will need to order/purchase a dedicated laboratory notebook. Here are guildlines on what to include in your laboratory notebook.

Quizzes: We will have in-class quizzes almost every week on Monday. To prepare for quizzes, you should read the assigned book chapter (at least once), review the lecture material, complete all of the homework problems, and review the homework solutions.

Tests: We will have a midterm exam before the end of the first (and third) quarters and a comprehensive final examination before the end of the second (and fourth) quarters.

Software: Logger Pro 3.15 Is an excellent data analysis software package. Download for Wndows 10, 8.1, 7, and for macOS 10.14, 10.13, 10.12, 10.11, 10.10. For more details on how to download and install Logger Pro click here.