20171020

Online reading assignment: interesting Midterm 1 physics topics

Physics 205A, fall semester 2017
Cuesta College, San Luis Obispo, CA

"2017-07 Phys 205A confusing"
Waifer X
flic.kr/p/ZC7p6g

Wordle.net tag cloud for interesting topics covered in Midterm 1, generated by responses from Physics 205A students at Cuesta College, San Luis Obispo, CA.

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

List at least three words describing interesting subjects covered in class (up through this midterm). (Graded for completion.)

These raw responses were subsequently edited to consolidate related common subjects.
How forces act on objects, the effects it causes on each force and the interaction between those forces.
projectile motion, Newton's laws
I'm not sure what this is asking.
Centripetal, Newton's first law, displacement
Centripetal force, centrifugal force, elastic energy
Projectile motion and free fall calculations.
Newton's laws of motion
static friction force
friction, projectile motion , kinematics
Newton's laws, different types of forces, acceleration and speed, velocity, mass, momentum, weight
Anvil, Newton's laws, projectile
uniform circular motion, friction, and Newton's laws
challenging, exciting, new
acceleration is imense, projectile motion is now more calculated to me, precise force
acceleration, pulleys, stiction
Newton's laws, velocity, accleration
Newton's laws, Uniform Circular Motion, and friction.
newton laws projectile motion
force, direction, magnitude
Projectile motion and motion graphs
Circular motion phenomena
Newton's laws, force, suspension
Distance vs. displacement, centripetal force, Newton's laws
Vectors, kinetic and static friction, Uniform circular motion
Describe your most interesting subject, and briefly explain why this subject confused you. (Graded for completion.)

The following are all of the student responses to this question, verbatim and unedited.
"Maybe uniform circular motion, because it is harder to understand compared to all the other subjects, the forces act differently."

"I like projectile motion problems because it is like a puzzle and the problems are concrete."

"None is particularly that interesting."

"Calculus chain of pain."

"Centripetal force is the most interesting as I never once thought there was a pull towards the center of any circular motion."

"Projectile motion because I ride mountain bikes and use this conceptually every time I jump down a trail."

"Projectile motion, because it’s real life applications are interesting."

"Newton's laws were the most interesting because they apply to other classes that I am taking."

"Projectile motion because it can be applied to everyday life."

"I find it interesting that things hit the ground at the same time when one is dropped versus the other being horizontally moved somehow. not always the case im sure but its interesting. I go to the range with my grandpa and shoot guns and for some reason it makes me think of bullets and when they will hit the ground in a way. Not exactly the same type of thing im sure but yeah. The most interesting subject for me in this class so far is anything that has a strong, easily perceptible application to a real-world situation. Abstract mathematical physics problems are not only boring to me, they become useless when I don't really learn them - which is what happens when it is difficult to translate what is happening in the equation/problem to real life."

"Newton's second law of uniform circular motion is pretty interesting to me because it's not as intuitive as some other concepts."

"I found that the labs were very interesting, but that's about it."

"Learning that it takes more force to get something moving than it does to keep it moving was interesting because I had never thought about it that way before."

"The most interesting subject to me so far is projectile motion. The idea of an object free falling and eventually reaching a constant terminal velocity was hard to grasp for a second. It was interesting to think that if you free fell from a certain height, even a mile higher you would not hit the ground any harder."

"Stiction is by far the most interesting aspect of this unit for me. Different materials have different static friction coefficients, which relates directly to molecular bonding and partial charges."

"I think the using the forces were most interesting to me because I like the idea of biomechanics."

"I think that uniform circular motion was the most interesting because it is one of those things I never really thought about how it worked before and now it makes sense."

"I personally like projectile motion because the ability to calculate the path of a thrown object is very helpful as a programmer with an interest in games."

"I thought that uniform circular motion was fascinating; something that I was able to observe in the real world was finally explained. The practice problem involving water in a bucket was especially interesting, as it tied net force and normal force together in a new way that was especially great for a visual learner like myself."

"I feel like the projectile motion will be the most interesting to me, because my brain works on seeing things that way. I am currently learning how to fly airplanes and this is one thing that we constantly have to take into consideration especially as we are climbing to avoid obstacles or coming in to land."

"Circular motion, because its applicable in many real-life situations."

"I find suspension and the forces that are involved in suspension to be interesting. I think the reason is because I am highly afraid of elevators so it's interesting to see how they work regarding physics."

"I thought the discussion of Newton's laws was very interesting. I only briefly learned about them in high school but once I got to learn about them in depth, it was very interesting."

"Vectors--due to a failure in the online enrollement system, I finished all my engineering classes before doing any physics, I loved working on vectors and tension."

Online reading assignment: confusing Midterm 1 physics topics

Physics 205A, fall semester 2017
Cuesta College, San Luis Obispo, CA

"2017-07 Phys 205A confusing"
Waifer X
flic.kr/p/ZC7p5K

Wordle.net tag cloud for confusing topics covered in Midterm 1, generated by responses from Physics 205A students at Cuesta College, San Luis Obispo, CA.

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

List at least three words describing confusing subjects covered in class (up through this midterm). (Graded for completion.)

These raw responses were subsequently edited to consolidate related common subjects.
Uniform Circular motion, is by far the most confusing
circular motion problems
Again, not sure what this is asking.
Calculus chain of pain
Horizontal vs. vertical, truncating-to-one-uncertain-sig-fig
Circular motion was tricky to grasp but I am figuring it out now.
Uniform circular motion
Uniform circular motion
newtons laws, forces, projectile motion
figuring out the best equation to use; assuming things that aren't stated, and just word play when talking about forces acting upon objects. Sometimes I think that could have been worded differently to make it less confusing.
Air resistance, circular motion, normal force free body diagram
To be honest I'm a little lost on the whole concept.
challenging, difficult, a lot of information
stubborn Newtons's laws, jumbled constant acceleration equations, and plentiful SI prefixes
sums, centripetal, stiction
Projectile motion, Newton's third law was a little confusing in the beginning, static friction was a little confusing as well.
Newton's second law
Newton's laws, static, kinetic
Describing the forces, uniform circular motion
Newton's laws applications
Projectile motion, velocity components
Centripetal force is something that I am having a lot of trouble on. I don't get the core concept nor am I able to do example problems relating to it.
Wording Newton's laws, understanding the questions that ask for reasoning rather than solving problems."
Describe your most confusing subject, and briefly explain why this subject confused you. (Graded for completion.)

The following are all of the student responses to this question, verbatim and unedited.
"I think uniform circular motion is the most confusing because, it is something I had never learned before and it combines a bunch of different ways in which the forces act."

"Circular motion is the most confusing because we did not spend much time on it."

"How to apply everything in a situation."

"Newton's third law, I have trouble with how it differs from Newton's first law."

"The difference between horizontal and vertical velocities. It took me a bit to fully understand this concept."

"Circular motion and the forces that are involved seemed to be the hardest part of this midterm material. From real-life experiences, I would have though the forces would be the opposite of what they actually are mathematically."

"Free body diagrams for uniform circular motion or really most motions get really confusing for me and I get lost on where to go with them."

"I struggled understanding the sum of forces for uniform circular motion because I did not understand how they differed."

"Newton's laws were confusing because the first law and the third law are hard to distinguish for me."

"When I look at the problems and use common sense and can figure out which law or object is less or more, I know the answer but it's hard for me to explain why I know that's the answer."

"I am not entirely sure why, but the concept of circular motion was a hard one for me understand. It was confusing to me that the arrows would all be pointing inward on a diagram."

"I'm just not that good at drawing free body diagrams. "

"I'm a little rusty on Newton's laws."

"The different frictions are the most confusing to me because I get lost when we start talking about the applied forces and how many newtons it takes to get something to slide."

"The most confusing was friction force at the beginning as well as uniform circular motion."

"For me, it was the centripetal force and that the sum of the forces point inward."

"Projectile motion was the most confusing for me until I really looked into my trigonometry again since it has been a few years since I took trigonometry."

"Newton's second law because actually knowing when to use it instead of Newton's first law is still difficult for me for some reason, and I don't even know why."

"I'm still so 'stuck' on static and kinetic forces; no matter how much I try and conceptualize it, I can't for some reason. I understand the basics, but I'm worried it won't be enough to be acceptable on the exam."

"Uniform circular motion, because I have a hard explaining why the forces are the way that they are like comparing normal forces in two different cases."

"Newton's laws, I feel I understand the concepts just when it comes to applying all of them I sometimes put them in the wrong spot."

"I think I am going to have the hardest time with projectile motion because it just has a lot of concepts to remember and steps to take when solving problems. It's a little harder to visualize for me."

"Centripetal force makes no sense to me and I am very worried about it on the midterm."

"Often we use Newton's first law, but when it comes to Newton's third law, I am always doubting if I look at the right forces to answer 'POF-OST-ITO.'"

Astronomy current events question: Jupiter Icy Moons radar test

Astronomy 210L, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Giuseppe Sarri, Lorenzo Bruzzone, Olivier Witasse, and Markus Bauer, "Helicopter Test for Jupiter Icy Moons Radar" (September 26, 2017)
esa.int/Our_Activities/Space_Science/Helicopter_test_for_Jupiter_icy_moons_radar
The European Space Agency used __________ to test a radar boom to be used by its Jupiter Icy Moons Explorer spacecraft in 2029 to probe under the crust ice of Jupiter's moons:
(A) NASA's James Webb Space Telescope.
(B) a high-altitude balloon.
(C) the International Space Station.
(D) a submarine.
(E) a helicopter.

Correct answer: (E)

Student responses
Sections 70178, 70186
(A) : 3 students
(B) : 2 students
(C) : 2 students
(D) : 1 student
(E) : 29 students

Astronomy current events question: Mistastin Lake crater impact event temperatures

Astronomy 210L, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Aylin Woodward, "The Hottest Place Ever Recorded on Earth's Surface Was 2370°C" (September 13, 2017)
newscientist.com/article/mg23531433-600-found-the-hottest-place-ever-found-on-earths-surface/
Based on analysis of __________, an impact crater in Canada 40 million years ago generated the hottest temperatures experienced on Earth's surface.
(A) embedded gas bubbles in rocks.
(B) radioactive minerals.
(C) dried-out lake beds.
(D) dinosaur fossil DNA.
(E) semi-precious gemstones.

Correct answer: (E)

Student responses
Sections 70178, 70186
(A) : 1 student
(B) : 0 students
(C) : 2 students
(D) : 1 student
(E) : 34 students

Astronomy current events question: James Webb Space Telescope launch delay

Astronomy 210L, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Brian Dunbar, "NASA’s James Webb Space Telescope to be Launched Spring 2019" (September 28, 2017)
nasa.gov/feature/nasa-s-james-webb-space-telescope-to-be-launched-spring-2019
The launch for NASA's James Webb Space Telescope has been pushed back six months to early 2019, due to:
(A) launch pad hurricane damage.
(B) expected peak sunspot activity.
(C) additional assembly and testing time.
(D) SpaceX rocket availability.
(E) plutonium fuel pellet shortages.

Correct answer: (C)

Student responses
Sections 70178, 70186
(A) : 1 student
(B) : 4 students
(C) : 32 students
(D) : 1 student
(E) : 0 students

Physics midterm question: comparing distances traveled

Physics 205A Midterm 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

The x(t) graph of a Physics 205A student walking along a straight line is shown at right. The student started at x = 0 at t = 0. Discuss why the student traveled a farther distance from t = 0 to t = 7 s than the distance traveled from t = 7 s to t = 10 s. Explain your reasoning using the properties of position, distance traveled, and displacement.

Solution and grading rubric:
  • p:
    Correct. Supports claim that student traveled a farther distance from t = 0 to t = 7 s than from t = 7 s to t = 10 s by discussing:
    1. distance traveled counts both forwards and backwards motion, such that from t = 0 to t = 7 s the student traveled a total distance of 3 m (2 m in the forwards direction, then 1 m in the backwards direction); compared to
    2. the distance traveled by the student from t = 7 s to t = 10 s is 2 m (always in the forward direction).
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. At least discussion demonstrates general understanding of distinction between distance traveled and displacement, but does not compare differences in distances traveled for the two time intervals.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. May compare areas, slopes, elapsed times, average speeds and/or average velocities.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 70854, 70855
Exam code: midterm01mOoL
p: 25 students
r: 3 students
t: 10 students
v: 15 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 2030):

Physics midterm question: proposed POF-OSO-WTF test for Newton's first law forces

Physics 205A Midterm 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

A Physics 205A student proposes a three-part "POF-OSO-WTF" test for identifying a pair of forces related by Newton's first law:
__ POF = Pair of Opposite Forces
__ OSO = On the Same Object
__ WTF = With just Two Forces
Determine whether or not this "POF-OSO-WTF" test can correctly identify a pair of forces related by Newton's first law acting on a 600 kg load of cargo that rests on the bed of a stationary truck. Explain your reasoning using free-body diagram(s), the properties of forces, and Newton's laws.

Solution and grading rubric:
  • p:
    Correct. Complete free-body diagram, and discusses/demonstrates:
    1. that there are two forces acting on the 600 kg cargo load:
      weight force w of Earth on cargo load (downwards),
      normal force N of truck on cargo load (upwards); and
    2. since the cargo load is stationary, then from Newton's first law these two forces are equal in magnitude in order for the net force to be zero; then
    3. tests each part of the presumptive "POF-OSO-WTF" test for the cargo load, where the weight force and the normal force are the "Pair of Opposite Forces," and both act "On the Same Object" (the cargo load), and this test applies to the cargo load "With just Two Forces." (Note that it cannot be applied to the truck, even though Newton's first law applies to it as well, as there are three forces acting on it.)
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May apply the "POF-OST-WTF" test to forces on the truck (when instructed to identify a pair of forces acting on the cargo load), or to an interaction pair of forces (which are actually related by Newton's third law, despite being instructed to identify a pair of forces related by Newton's first law); but at least has (1)-(2) above complete and correct. Or may have (2)-(3) essentially complete/correct, but has minor errors in forces on free body diagram, such as involving forces that do not act on the cargo load, and/or forces exerted by the cargo load.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. Essentially only (1)-(2) complete/correct, but does not explicitly discuss relevance of "POF-OSO-WTF" test.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some substantive attempt at applying Newton's laws to a free-body diagram
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No systematic application of Newton's laws to the forces on a free-body diagram.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 70854, 70855
Exam code: midterm01mOoL
p: 32 students
r: 10 students
t: 8 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 5102):

Physics midterm question: comparing accelerations of sliding boxes

Physics 205A Midterm 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

Two 0.5 kg boxes are moving to the left, both slowing down while pushed to the right by an applied force of 10 N. Discuss why the box sliding on a frictionless floor will have a smaller magnitude of acceleration than the box sliding on a floor that has friction. Explain your reasoning using free-body diagram(s), the properties of forces, and Newton's laws.

Solution and grading rubric:
  • p:
    Correct. Complete free-body diagrams, and discusses/demonstrates:
    1. because both boxes are slowing down while moving to the left, Newton's second law applies along the horizontal direction, such that the net force (and acceleration) for each box must point to the right; and
    2. for the box on the frictionless floor, there is only horizontal force acting on the box:
      applied force Fapplied on the box (10 N, to the right),
      such that the net force on this box must be 10 N to the right; and
    3. for the box on the floor with friction, there are two horizontal forces acting on the box:
      applied force Fapplied on the box (10 N, to the right),
      kinetic friction force fk of floor on the box (? N, to the right),
      and since these two forces act in the same direction, the net force on this box is the addition of these two force magnitudes (10 N + ? N), and thus must be greater than 10 N;
    4. since the boxes have the same mass, the box with the greater net force magnitude will have the greater acceleration magnitude.
    (May have only implied (1) and (4) above, and/or ignored discussion of vertical forces and Newton's first law, as long as discussion of (2)-(3) is clear and complete.)
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have kinetic friction (or other) force vectors incorrectly drawn in opposite directions, additional forces (or other types of vectors) added in; but at least recognizes that for the box on the frictionless floor there is only one force that contributes to the net force, while for the box on the floor with friction there are two forces that contribute to the net force.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying Newton's laws to free-body diagram(s).
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No systematic application of Newton's laws to the forces on free-body diagram(s).
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 70854, 70855
Exam code: midterm01mOoL
p: 14 students
r: 19 students
t: 5 students
v: 14 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student):

Another sample "p" response (from student):

Yet nother sample "p" response (from student):

Physics midterm question: forces on string-twirled ball

Physics 205A Midterm 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

A Physics 205A student twirls a ball attached to a string in a vertical circle with constant speed. Discuss why it is possible for the tension force of her hand on the ball to have the same magnitude as the weight force of Earth on the ball, when the ball is swinging through the highest part of the circle. Explain your reasoning by using free-body diagram(s), the properties of forces and Newton's laws.

Solution and grading rubric:
  • p:
    Correct. Complete free-body diagram, and discusses/demonstrates:
    1. Newton's second law for uniform circular motion applies, such that while the ball is swinging through the highest part of the circle, the net force ΣF (of magnitude mv2/r) must point in towards the center of the circular motion--which is vertically downwards; and
    2. while the ball is swinging through the highest part of the circle, there are two forces acting on the ball:
      weight force w of Earth on the ball (mg, downwards);
      tension force T of hand on the ball (downwards),
    3. since both these two downwards forces add together to get the downwards net force, it is possible that they each have the same magnitude of one-half of mv2/r (for certain values of mass m, speed v, and radius r).
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Two of the three points (1)-(3) correct/complete.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. May argue T (upwards) = w (downwards) because of Newton's first law; or may draw T and w as both acting downwards but does not explicitly relate how Newton's second law requires a downwards net force that is met by their addition, and/or introduces normal forces, Newton's third law, etc.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some substantive attempt at applying Newton's laws to free-body diagram.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No systematic application of Newton's laws to the forces on free-body diagram.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 70854, 70855
Exam code: midterm01mOoL
p: 10 students
r: 7 students
t: 34 students
v: 11 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 4632):

Another sample "p" response (from student 8659):

A sample "t" response (from student 2500):

Physics midterm problem: world-record washing machine throw

Physics 205A Midterm 1, fall semester 2017
Cuesta College, San Luis Obispo, CA

"Washing Machine Throwing Showdown"
Guinness World Records
youtu.be/YC0oj7BcWiI

In 2017, Zydrunas Savickas set a world record throwing a 46 kg (101 lb) washing machine that landed a horizontal distance of 4.13 m from its starting position atop his head. Savickas' height is 1.91 m, and the washing machine was airborne for 1.84 s starting from just off the top of his head to just before hitting the ground[*].

Find both the horizontal and vertical components (v0x, v0y) of the initial velocity vector for the washing machine, as it was thrown and released from just above the top of Savickas' head. Neglect air resistance, and treat the washing machine as a point object. Show your work and explain your reasoning using properties of projectile motion.

[*] Rachel Swatman, "Watch Game of Thrones Star Take on World’s Strongest Man Winner in Washing Machine Throwing Showdown" (January 13, 2017), guinnessworldrecords.com/news/2017/1/watch-game-of-thrones-star-take-on-world%E2%80%99s-strongest-man-winner-in-washing-machi-458290.

Solution and grading rubric:
  • p:
    Correct. Discusses/demonstrates:
    1. uses given values of t = 1.84 s and x = +4.13 m to solve for the initial (and constant) horizontal velocity v0x (where t0 = 0, x0 = 0); and
    2. uses given values of t = 1.84 s and y = −1.91 m to solve for the initial vertical velocity v0y (where t0 = 0, y0 = 0).
  • r:
    Nearly correct, but includes minor math errors. May have intentionally or unintentionally used y = +1.91 m or y = 0 instead of y = −1.91 m.
  • t:
    Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least has one initial velocity component correct, but other component has errors in addition to those listed in (r), such as setting vy = 0 in y = (1/2)⋅(vy0 + vy)⋅t to solve for vy0, or setting vx = 0 in x = (1/2)⋅(v0x + vx)⋅t to solve for vx0, etc.
  • v:
    Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner.
  • x:
    Implementation of ideas, but credit given for effort rather than merit.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 70854, 70855
Exam code: midterm01mOoL
p: 20 students
r: 16 students
t: 12 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 1956):