Week 10: October 18th (return to previous unit)

Learning Objective Summary:______

In nature, objects in motion tend to stay in motion in a straight line, unless an unbalanced force acts on them. This chapter illustrates that if we see an object entering a curved path, it is because a force must be acting on it, perpendicular to the velocity. This chapter introduces how students can both determine the magnitude of that force as well as identifying the cause of the force.

New assignments this week

• chpt 5 text problems 4, 6, 7, 8, 10 (page 130)
• Soap on a rope! (aka swinging a mass in a verticle plane)! Click here to see handout.

The Event Horizon Research Project. This is a recording of the press conference describing how astrophysicts were able to create an image of the black hole in the center of the galaxy called M87.

Discussion point: Acceleration is a change in velocity.. up to this point, accelerations were seen as changes in speed only (systems were linear), but now, accelerations are changes in direction and speed is not changing.

Discussion: What forces create centripital accelerations? Note: the equation for centripital force only describes the magnitude of the net, centripital force, not what the cuase of that force is.

Sample problem/demo 1. A coin is placed on a record which is spinning faster and faster. When the record player reaches 20 R.P.M, the coin slides off (i.e., no longer "sticks"). If the coin was placed 15 cm from the center of rotation, what must the coefficient of friction be to have kept in place? (similar to problem 12 in text).

Sample problem/demo 3. Clark stood on desk top and modeled a "tetherball" system. In this case, all that was provided to students was mass at the end of the string and the length of the string itself. Students then observed "the tetherball" swinging around and were challenged to identify (and estimate!) additional values required to determine the tension in the string (several ways to solve, depending on which values the students could pull from observing the system).

Sample problem 2. (problem 18 in text). Rotor-ride, people enter a circular room and are flung against the wall as the system speeds up. If system is spinning at 1/2 rotation per second, what must coefficient of friction be such that folks don't slide down the wall?

Swinging on a rope swing is a study in centripital forces. Which forces create the most fun? If the girl weighs 100 lbs, what force must she hang on with in this picture?

Stephen Colbert speaks with Maurice Sendak about his book idea, I am a pole and so can you. (7 minutes)

Demonstration/discussion: Bucket of water of my head.. what is the tension in my arm as I swing the bucket in giant circle up and over my head? (top and bottom points are the main focus).

Mini-lab: Rock swinging over your head! Given a mass and length of string, determine the slowest speed you can spin it at such that the tension in the string goes to zero at the top but the mass still undergoes a circular path.. Students measured the radius (basically the length of the string with end points being the center of mass on one side and the center of rotation of their hand on the other) Click here to see handout.

Week 2: October 25

New assignments this week.

• Chpt 5 Sample problems: 11, 13, 15, 19, 21.
• Battle of the X planes. (notes on the first hour of the video).

• Meteor impact on Earth. (from A short history of nearly everything). Students were to create an illustration/drawing the students 'vision' of what the last moment looked like!

Clark was out on Monday and Tuesday due to developing cold symptoms.. (which required a mandatory COVID test).

Students watched: Battle of the X-Planes and took notes from the first hour of the film.

Discussion: Banked road curves and determining the ideal banking angle for icy (frictionless) conditions. (described in section 5.3 of text). (youtube: the high banks of Daytona Speedway). (a test drive for a newbie) (Nascar 2015. Austin Dillon Crash at nearly 200 mph) just for fun, a BMW 850 doing ~185 mph

Discussion: Using conservation of energy to determine the "true" velocity of the previous week's "rock in a circle over the head" mini-lab (also, an introduction to chapter 6 in the text: Energy and the Work-Energy theorem). This conversation had students determing the "drop" distance of their verticle plane.. As the mass falls through that distance, d, the mass accelerates by a an easily determined amount. This adjusted value then is added to the original "top of path" value which then allows us to predict the Average Speed at which the rock will traverse the circlular path, in much greater alignment with the measured values seen last week. (see sections 6.1 and 6.3 in text)

All about NASCAR racing

Week 3: Nov 01

No new homework this week. Test on Thursday!

Additional resources:

• The Zero gravity plane
• 2001 a space odyssey station (fictional, as imagined back in the late 1960s)

• running inside the imagined 2001 space station

Class activity: Determine the ideal bank angle for curve on Sir Francis Drake Blvd. We used Google Earth to estimate the radius of curvature of a turn on Sir Francis Drake Blvd.. and the coupled with the "speed limit" speed of 35 mph.. determined the ideal banking angle. (click here for photo of Clark measuring slope of road towards radius).

Discussion: Problem 21 from last week's homework set.

Discussion/ Sample problem: Chpt 6 # 42: At what minimum height, h, must a frictionless block (a hot wheels car?) be released from such that it is able to complete the "loop de'loop" without falling down. (loop of radius r).

video clip/discussion: Hot Wheels "Verticle -loop" challenge . Same problem as above with a twist. How fast must these cars be travelling before they "hit the loop" in order not to die? Follow up: Human "loop the loop".

Week 4: Nov 08

New assignments this week.

• Video Summary: Einsteins Big Idea (the first hour).
• Chpt 6 problems: 2, 7, 8, 13 20 (page 162)
• Spring lab Part 1: Characterizing a Spring.

Additional resources:

• Oumuamua is the first 'interstellar object' we've seen!

Clark was out on Monday, which was a Tuesday bell schedule (Thursday is Vetrans Day)

Video: Einsteins big idea. Students watched the first hour in class, through the sequence with Emilie Du Chatelete. Students were to summarize the key elements of each section.

Discussion: systems that behave like "springs".. Springs exhibit restoring forces which are proportional to their displacement from zero. The stiffness of the spring is described by the spring constant, K. The spring constant can be determined by plotting the force required to displace it (force on Y axis and displacement on x axis). The work required to compress a srping (or the energy stored in that same compressed spring) can be determined by using the formula PEspring = 1/2kx^2. Clark used a bow (as in, a bow and arrow).. as a sample "spring system" (other examples included a meter stick as a diving board, several coil springs, and a plastic cylinder of air)..

characterizing springs involves determining their stiffness (the spring constant, k) and the range of motion they will be operating through. (many objects or systems behave like springs including diving boards, airplane wings, cylinders of air (air shocks), and most rigid materials/systems (they will "flex under load).

Week 5: Nov 15

New assignments this week.

• Lab: Using conservation of energy to determine the height that a mass will get thrown into the air by a compressed spring.

Demo/practice problem: #42 (chpt 6).. A bungee jumper falls 31 meters attache to a bungee chord 12 meters long. Determine K and max acceleration (and max force she feels).

Lab activity: Characterizing race-car springs. . Using a variety of masses to load the spring, students determined the spring constant of the plastic physics, spring-loaded car.. Recording raw data, converting into the frame of reference "of the spring".. determining the slope and the "offset" of the captured spring. How much of the energy can we actually access? (extrapolate the line to find the x-intercept). (click here for the guided worksheet)

Week 6: Nov 22\

Thanksgiving week holiday.

for next year:

• Chapter 6 problems: 36, 42, 58.
• Chapter 6 problems: 40, 45, 48, 49, 50.
• Demo/practice problem: #42 (chpt 6).. A bungee jumper falls 31 meters attache to a bungee chord 12 meters long. Determine K and max acceleration (and max force she feels).

Week 7: Nov 29

New Assigments this week.

• Text Notes: Chapter 7. pages 167-172
• Reading: Meteor Strike. see text at right.
• Video: Europa Report. Students are to take notes on the film as it rolls, then rewrite them in the 'correct order' of events. (the film plays in a scrambled order). Also, students should reflect on which parts seem reasonable and which parts seem fictitious.

Week 8: Dec 06

New Assignments:

Chapter 7.1-7.3 notes.

Chapter 7.4-7.6 notes.

Chapter 7 problems. 4, 5, 6, 7, 10.

Week 1 (of new semester). Jan 03.

New Assignments this week.

• Lab assignment: Using "smart cars".. to create a collision, and then show that momentum is conserved and to determine the force of the collision based on the impulse (change in momentum x duration of collision).

School started on Wednesday (which was a Monday schedule).

Class only met one full day this week (Friday).

Review of the concept of momentum and Newtons original statement of F = ma.

Discussion: Momentum WITHIN A SYSTEM is always conserved.

m1v1 + m2v2 = m1v1' + m2v2' (with the number of terms equaling the number of elements in the system).

Lab assignment: Using "smart cars".. to create a collision, and then show that momentum is conserved and to determine the force of the collision based on the impulse (change in momentum x duration of collision). Details include; determining where in the data set the 'moment of interest' is displayed, correcting for the 'reverse' velocity data for the car facing backwards and adding the momentum of the two cars to show the summation is constant through the collision event.

The physics of traffic collisions website.

Week 2: Jan 10.

New Assignments this week.

• Chapter 7 problems: 12, 15, 16, 19, 21
• Lab: Determining the impulse in a collision.
• center of mass mini-lab:

Demo problem: 13. A two-stage rocket separates after launch. The 'separation' velocity is given. Students are to determine the absolute velocities of each 'stage' after the separation.

Lab: Determining the impulse in a collision. This lab has students collecting velocity and force data for one car only. The student then plots the momentum for the car through the collision event and measures directly, the change in momentum.. and then plots the force data as a function of time to generate a force/time graph. The student then writes a function to determine the area under the curve..(integrates the function) which also reprsents the impulse and compares that to the graph of delta P.

Demo problem: 14

Discusssion: Center of mass. .with mini-lab.

Introduction to Center of mass (section 7.8 in Text): Discussion: Newton's ideas re: gravity, distributed mass systems and his deveopment of the equation for the force of gravity. Mathematically, distributed mass systems can be treated as if all of the mass exists at a geometric point. Demo's of how objects naturally rotate about their center of mass including throwing a tennis ball (symetrical) and a hammer (asymetrical) into the air. Finally, an introduction to equation for Xcm of a linearly distributed-mass system.

Mini-lab: Students placed weights on meter sticks and suspended the "system" from a giant binder clip. Students then used the equation for Xcm to determine the center of mass (balance point) and compare to their observations.

Discussion of Impulse (delta P) on systems and force vs time graphs as a tool to determine changes in momentum.

Introduction to rotating systems (chpt 8.1 and 8.2 in text). Radians as a unit of measurement as well as how to describe rotational accelerations were explored.

Week 3: Jan 17.

just for interest: Volcanic eruption near Tonga

New Assignments this week.

• mini lab: Sit and Spin.
• Chapter 7 problems: 46, 49, 50, 51, 52.
• mini lab: Feel the torque!

Monday was a holiday! (MLK day)

Discussion: Problem 21 in text (chpt 8). From what height can a dude jump and not break his legs!

Discussion: (Continued from last class) How to calculate Center of mass when mass is spread over an X/Y plane.. (short version; calculate along one axis at a time).

Introduction to chapter 8 and rotational dynamics..

• Units.. Theta, omega, alpha.. what is a radian?
• Mini-lab: Sit and Spin. Students took turns sitting on rotating lab stools.. first trying to determine their 'max comfortable' rotating speed (omega, rads/sec) and then the deceleration of the system due to bearing friction (alpha, rad/sec^2)

Introduction to Torque.. (chpt 8.4 in text). Units, basic principals, etc. use of wrenches and "cheater pipes")

Mini-lab: Feel the torque! students placed weights at (3) different positions on a meter stick and determined (and experienced!) the torque produced. Additionally, students fixed a single weight onto the end of the meter stick and held it at three different angles (as measured from the horizontal) ranging from "flat" to "verticle" and once again, determined and experienced the torque produced.

The biggest jet engine

Week 4: Jan 24.

Test Announcement: This Thursday! covering the following sections:

• 7.1 Momentum and Force
• 7.2 Conservation of momentum
• 7.3 Collisions and impulse
• 7.4 Conservation of energy and momentum in collisions
• 7.5 Elastic collisions
• 7.6 Inelastic collisions
• 7.8 Center of mass
• 8.1 Angular quantities
• 8.2 Constant Angular acceleration
• 8.4 Torque.

New assignments this week.

• Mini-lab: Feel the moment.

Derivation of various moment of inertia

Discussion/introduction: Moment of rotational inertia. In linear systems, F=ma, mass is easy to measure AND remains constant. In rotating systems, Torque = I (alpha). The term I, called the moment of inertia of a rotating system is a function of both a systems mass AND its distribution. The main question is, how far is the mass from the axis of rotation. Each geometry has a unique expression (function) for the moment of inertia and students will use tables (such as this one) to calculate.

Mini-lab: Feel the moment. (aka: Rotating symnetrical objects about different centers). For each of the following, four scenarios, students calculated the moments of inertia and then wrote short haikus or poems describing how the changing moments of inertia "felt" in comparison to each other.

1. An aluminium rod about its center and about one end
2. A 1 kg mass held at arms length and again with your elbow close to your body (rotating your forearm back and forth).
3. A text book around one edge (axis is parallel to edge) and spun about it's center (like spinning a basketball)

TEST ON THURSDAY!

Here comes a fast ball!

Discussion/Demo: Angular momentum (defined) and how it is conserved within systems. Discussion began with a review of conservation in linear systems, highlighting that the concept is most valuable when "events" such as collisions or explosions occur.

Demo/discussion: Using vectors to represent angular quantities.

• (1): Vectors represent angular speed, torque, momentum and acceleration.. Vector math allows us to understand why a spining bike wheel doesn't fall down when suspended by a rope on one side.
• (2) vectors represent angular momentum, which must be conserved with-in systems. A student holding a spinning bike wheel horizontally rotates it 180 degrees. As a result, the student starts to rotate.. the two-component system must maintain the system, rotational inertia. Vectors allow us to easily predict this.

Week 5: Jan 31.

New assignments this week.

• Fixed torque accelerates rotating platform. (see description at right). Formal write up, no more than 3 to a group.
• Lecture rewrite: A spinning wheel doesn't fall. (see text at right).

Test was on Tuesday.

Lab (w/blue-tooth devices). Fixed torque generates acceleration of rotating system..Students modeled rotating systems using basic geometric distributions of masses (plates rotating about a center and a single mass rotating a fixed distance away from the center of mass, etc.). Then, using a known torque (a known weight connected via a threa to a known radius pully) captured high frequency data of rotational velocity which, when plotted in excell, gave acceleration data (the slope of the graph). With this information, students were able to determine the "measured" intertia of the system which was then compared to the predicted inertia of the system.

Lecture rewrite: Spinning wheel doesn't fall. The discussion began with the importance of using pictures to 'visualize' each problem. This is especially challenging with vector math describing rotating systems. Clark then proceeded to 'walk through' an explanation of why a spinning wheel doesn't fall.. and revisited how we use vectors in these circumstances. The students then had the challenge (the assignment) of taking careful notes, and then 'repackaging them' as if they were writing an 'illustrated text book' discussion of this demonstration.

Discussion for next week: Why don't we fall? (answer! Vector math!)

Week 6: Feb. 07.

New assignments this week.

• Chapter 8: problems 26, 30, 54, 56, 78.
• One page essay: Hidden Figures. (assignment at right).

Additional resources:

• Extra Credit! Listen to this Podcast on the science of friction and write a one-page summary! (5 pts ec).
• Angular momentum humor (and explanation)

Demonstration/class discussion: Why does a rolling and wobbling wheel 'straighten' itself out? (Clark rolled the bike wheel down the hallway and intentionally got it 'wobbling'.. as the wheel rolled along, the wobbles dampened out and the wheel rolled straight and true. As a group challenge, the students attempted to use rotational dynamics vectors to explain the 'self-leveling' effect of the wheel.

Introduction to fluid dynamics with Physics Girl! This video explores the formation of vorteces in fluids, which are the result of rotational momentum imparted to the fluid itself.

Video/History: Hidden Figures. This video portrays the lifes and times of four African American women who worked for NASA in the 1960s during a time of tremendous civil unrest. (the film is on Amazon Prime Video). Students were to write up a one page response to the following questions: (1) What were the circumstances that allowed these women to work for Nasa during a time of tremendous discrimination? (2) Why did it take so long for this story to come out?

Introduction to vibrations, waves and accoustics.. and the upcoming Guitar Project..

Week 5: Dec 02

New assignments this week.

• Text notes: Example 5-14: Determine the height above the surface of the Earth such that a satelite will stay in a geosynchronous orbit. (pg 123).

• Chpt 6 questions: 2, 3, 4, 9, 11
• Chpt 6 problems 21, 36.
• reviewing sections :6.1 Work done by a constant force, section:6.3 Kinetic Energy and the Work Energy principal and section:6.4 Potential Energy due to gravity.

New assignments this week.

• Chpt 6, probs: 36, 40, 42, 45, 48.

Video: Car Crash physics. This History Channel documentary reviews the history of safety improvements in automobile and road design following years of horrific crashes. Tons of great footage of the early days, when there were no 'rules of the road', cars were made of wood, seatbelts weren't included in cars. (notes for extra credit).

Review of energy transformations/demo: Clark threw a book across the table. The book skidded to a stop over a distance (of approximately 1.5 meters). Using conservation of energy, students determined the intiial velocity of the book.. comparisions were made to the CHP which uses length of skid marks to determine "speed of vehicle" before the accident (CHP officers are trained to estimate the coefficient of friction for different situations)..Students also estimated the coefficient of friction for this situation (~.3) as part of the solution discussion.

Week 6: Dec 09

• Bungee Jumping.. with adjustable "depth" of plunge into water..
• Throwing people in wheel-chairs off of bridges (shouldn't there be a law against this?
• German dude isn't having fun.

Discussion/video clip: History of science. Emilie du Chatlier (in the 1700s). This clip (starts at the 55 minute mark) explores how a 17 year old girl in the year 1780 promotes the new ideas of kinetic energy.

Week 1 (Spring Semester). Jan 08.

New assignments this week.

Week 2 (Spring Semester). Jan 15.

No School on Monday. MLK day.

New assignments this week.

• Chpt 7 probs: 7, 10, 13, 21.

Wednesday is all periods (Monday schedule)

Pass back final exams and final grade reports from last semester.

How long does it take to orbit the moon or Earth?

Week 6: Dec 05

New assignments this week.

• lab activity: Push the go button: See text at right. Students may work in groups of up to 3 students to document, illustrate the car accelerating up the ramp. The objective is to compare kinetamic models to models based on conservation of energy.
• Chapter 6 problems: 40, 45, 48, 49, 50.
• Test corrections, last week's quiz.

What you should also be working on.

• Chapter 6 problems: 36, 42, 58.

Additional resources: (speaking of fast cars)

• Mercedes engines, super efficient, modern, fuel injected engines. biturbo, even cooler!
• History of jet engines: Modern Marvels.
• Inside the 1000 mph car..

Demo/practice problem: Clark placed a mass (200g) on a meter stick at the 80 cm mark. He then balanced/suspended it by hanging it from a thread at the 71 cm mark. Students then determined the mass of the meter stick based on this "balance problem".

Discussion/introduction: Conservation of momentum in elastic and inelastic collisions. When can we also use conservation of energy? Only during elastic collisions. Clark set up a series of "collisions" on the aluminimum track in front of the class room.

Lab: Car down ramp crashes into book. Students loaded a toy car with weights and then rolled it down a ramp into a parked book. The combination then slid a distance before coming to rest. Momentum was conserved during the collision so students were able to determine the speed at which the combination started off at and then, using conservation of energy, conservation of momentum and the "work done by friction", were able to determine the coefficient of friction between the book and the table. Lab summary due next week.

Review of using MS Excell to plot datta and determine the slope and function of the line.

Discussion/lab activity: Push the go button:. How will that energy be unleashed? When does the work happen? What will be the speed of the car be as piston hits the end of its range? Given this speed and the slope of the plane, what does kinematics say the max distance up the ramp will be? How does this compare to what conservation of energy predicts? Students loaded their springs, measure the angle of their ramp, predicted and measured the distance up the incline plane (and total, change in altitude). Students may work in groups of up to three people to illustrate, discuss how kinematic forces models compare to conservation of energy models.

Video: Car crash physics.. this history channel film discusses the evolution of automotive safety standards both in the design of roads (i.e., banking turns and the structures of road signs and guard-rails) and the designs of cars themselves (including seatbelts and "crumple zones"). Introduction to momentum: P = MV.,, demos.. of same..

Week 1: Spring semester! (week of Jan 09)

New assignments this week.

• Chpt 7 probs: 46, 49, 50, 51
• Center of mass mini-lab(cut out shape plus weights on meter stick, see text at right).

Week 2: Jan 16.

New assignments this week.

• Chpt 8 HW Probs: 4, 15, 18, 22, 24
• Mini-lab: Radians per second.
• Mini-lab: Feel the torque!
• Torque basics worksheet. (click here to download). (choose two problems to illustrate)

What you should also be working on.

• Chpt 8 HW Probs: 3, 8, Questions: 4, 6, 8

Additional resources

• History Channel: Cranes..
• Crane Fail compilation

Mini-lab/Radians per second: determining a comfortable speed of rotation in rad/sec and RPM.. AND.. determining the decleration value in radians per sec^2. Due end of period.

Video: Einstein's big idea. This video illustrates early scientists ideas of energy and how energy is conserved.. Micheal Faraday, Sir Humphry Davey, Anton La Voisier, Emily Du Chatelet are all introduced as major contributors to Einsteins work. (first 20 minutes today, focusing on Micheal Faradays work with electricty).

In-class time to work on torque basics worksheet. (click here to download). Due end of week.

Week 3: Jan 23.

New assignments this week.

• Chpt 8 HW problems: 25, 26, 30, 33, 35.
• Cornell notes: Infinite secrets. (see text at right)
• Lab: Determining the moments of inertia for various shapes (see text at right)
• Lab: Determining the breaking torque of a classroom stool.

What you should also be working on.

• Chpt 8 HW questions: 5, 9, 16, 22
• Chpt 8 HW problems: 38, 40

Additional resources

• derivation of function for asymetric system

Video: Einstein's big idea. (continuing into Anton La Voisier discovering that mass is conserved in chemical reaction and Emily Du Chatelet disovering that squaring the velocity more precisely reflects the conservation of energy)

Demo: Rolling round things down an incline.

New assignments this week.

• chpt 8 probs: 39, 51, 54, 56, 60

What you should also be working on.

• Chpt 8 problems 34, 41.

Studying for next week's Quiz ON THURSDAY

• 7.8 Center of mass
• 8.1 Angular Quantities
• 8.2 Constant Angular Acceleration
• 8.4 Torque
• 8.5 Rotational Dynamics
• 8.6 Solving problems
• 8.8 Rotational Momentum
• 8.9 Vector Nature of angular quantities

Quiz 1: Basics of center of mass, torque, rational dynamic equations radial measurements.

Demo: The total inertia is the sum of the inertias.. (class table top demos).. Disc with a ring on top, bar with a mass on one end.. (using tables).

Discussion/demo problem: Putting torque, moment of inertia and acceleration all together. Accelerating the bike wheel with a fixed force. Question: How much force do I need to apply to accelerate the wheel at "alpha" radians per second? If I were able to give that force, how long would I need to exert it in order to get the wheel up to 100 rpm? (unit conversions)

Discussion/ demonstration: Conservation of angular momentum.Angular momentum is conserved! Just like in linear systems, once a mass "gets moving" (whether in a straight line or rotating), they don't want to slow down. Analagous to P= MV for linear systems (momentum is the product of mass and velocity and remains CONSTANT, rotating systems have Angular momentum (L) = Moment of inertia x omega. (same as mass times velocity in a linear system).

Sample problem/discussion: Chpt 8 problem #41. The "atwood" machine. Two masses are attached by a rope to a pulley. The entire system accelerates at a constant rate. Determine the rate of acceleration. (the key is translating the linear acceleration of the edge of the wheel to the angular acceleration due to the applied torques).

lab: Determination of braking torque in our "rotating stools". Students were tasked with determining the torque that our lab-stools apply to them as they rotate. To accomplish this, students must first calculate their "moment of inertia" by modeling their bodies as a collection of simpler parts. Once that is done, students simply got themselves spinning up to a "fun" speed, and measured the time it took to coast down to a stop, providing "alpha" (the angular deceleration) so that they could use the equation torque = I alpha. (students were to work with groups of UP TO three (3) students).

Test 1: rotational dynamics

extra credit, follow up pop quiz: Why are bicycle's "self correcting" (when riding with no hands?). Groups of three.. vectors are required to answer.

Discussion: The physics, engineering and "trade offs" in competing in the famous, 24-hours of LeMons race in France. Its all about horsepower, weight, aero-dynamics and tires.

• Typical, rear engine GTP cars (most, modern exotic Ferraris, Audies, Maseratis, etc.. are based on this design).
• The Nissan GT-R LM Nismo.. a front wheel drive, "hyrbrid" car driven by a video-game winner.
• The local, low-buck version of the race called 24-hours of Lemons.. (hosted yearly at Sonoma Race Way, formerly called SEARS POINT racetrack).

Additional resources

• bionic eyes! (contact lenses with built in telescopes)
  

Demo-problem/discussion: #30 from text: A potter's wheel is slowed by the friction of the potters hand. Determine the time it takes to come to rest.

Sample problem (generic version of #60). A wheel is rotating and a second mass is dropped on top. using conservation of angular momentum, determine the new angular velocity?

Modeling systems Part II. Students sat in the "spinning lab stools", holding heavy books at arm's length.. and attemped to determine the "braking torque" of the stool's bearing packs. To do so required placing a rotational transducer in their lap to record changing velocity and building a model of inertia of the student's (and chair's) mass distribution. Standard Lab Summary format (limited to three people per write up).. describing solution. Since there is no "answer key", different groups attempted to model the same chair, to compare answers.