20171117

Physics quiz question: moment of inertia of ring vs. smaller disk of same mass

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA

A ring and a solid disk rotate about their centers. The ring and the solid disk each have the same mass of 1.2 kg. The ring has a radius of 0.25 m, and the solid disk has a smaller radius than the ring. (Iring = M·R2, Idisk = (1/2)·M·R2.)

The rotational inertia of the ring is __________ the rotational inertia of the solid disk.
(A) less than.
(B) equal to.
(C) greater than.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (C)

The rotational inertia of the ring of mass M = 1.2 kg and radius R = 0.25 m is:

Iring = M·R2 = (1.2 kg)·(0.25 m)2 = 0.075 kg·m2.

The rotational inertia of the disk of mass M = 1.2 kg and a radius smaller than 0.25 m, along with the factor of (1/2) then must be smaller than the rotational inertia of the ring:

Idisk = (1/2)·M·R2 = (1/2)·(1.2 kg)·(some value less than 0.25 m)2,

such that Iring > Idisk.

Sections 70854, 70855
Exam code: quiz05nWaW
(A) : 6 students
(B) : 4 students
(C) : 39 students
(D) : 0 students

Success level: 80%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.34

Physics quiz question: comparing lever arms for loaded beam forces

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA

A uniform beam with a mass of 10 kg and length 2.0 m has a 3.0 kg load hanging from its end, and is suspended by a horizontal cable attached to a wall. (Calculate all torques with respect to the pivot.) The __________ force has the longest perpendicular lever arm.
(A) horizontal cable tension.
(B) beam weight.
(C) load.
(D) (There is a tie.)

Correct answer (highlight to unhide): (A)

The weight of the boom acts at its center of gravity, straight downwards. The perpendicular lever arm ℓw for the weight force w extends from the pivot to perpendicularly intercept the weight force line of action, such that this will be a horizontal line of length:

w = (1.0 m)·cos(70°) = 0.34 m.

Similarly the perpendicular lever arm ℓload for the load force Fload extends from the pivot to the perpendicularly intercept the load force of action, such that:

load = (2.0 m)·cos(70°) = 0.68 m.

The perpendicular lever arm for the horizontal cable force extends from the pivot point to perpendicularly intercept the tension force of action, such that:

cable = (2.0 m)·sin(70°) = 1.9 m.

Sections 70854, 70855
Exam code: quiz05nWaW
(A) : 21 students
(B) : 11 students
(C) : 14 students
(D) : 3 students

Success level: 43%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.53

Physics quiz question: water pressure at bottom of graduated cylinder

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA

A graduated cylinder is filled with 10 cm of water. The top of the water level is exposed to atmospheric pressure (Patm = 101.3 kPa). The density of water is ρwater = 1.00×103 kg/m3. The water pressure at the bottom of graduated cylinder is:
(A) 1.0×102 Pa.
(B) 9.8×102 Pa.
(C) 1.003×105 Pa.
(D) 1.023×105 Pa.

Correct answer (highlight to unhide): (D)

For static fluids, the energy density relation between pressure and changes in elevation is given by:

0 = ∆P + ρ·g·∆y,

0 = (PbottomPtop) + ρwater·g·(ybottomytop),

where the air pressure at the water surface at the top of the graduated cylinder is 101.3 kPa = 1.013×105 Pa, such that:

Pbottom = Ptop – ρwater·g·(ybottomytop),

Pbottom = 1.013×105 Pa – (1.00×103 kg/m3)·(9.80 m/s2)·((–0.10 m) – (0 m)),

Pbottom = 1.013×105 Pa – 0.0098×105 Pa = 1.023×105 Pa.

(Response (A) is ρwater·∆y; response (B) is ρwater·g·∆y, which is the relative pressure difference between the top and bottom of the water in the graduated cylinder; response (C) is Ptop + ρwater·g·(ybottomytop).)

Sections 70854, 70855
Exam code: quiz05nWaW
(A) : 2 students
(B) : 11 students
(C) : 15 students
(D) : 21 students

Success level: 43%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.28

Physics quiz question: weights of comparable floaters

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA

Two solid objects of different sizes both float with 75% of their volumes below water. It is 
not known whether these objects are made of the same material. The __________ object has a greater weight.
(A) smaller.
(B) larger.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The magnitude of the buoyant force is given by:

FB = ρfluid·g·(Volume submerged),

where the density ρ is of the surrounding fluid (water) and the gravitational constant g = 9.80 m/s2. Since the volume of water displaced by the smaller object is less than the volume of water displaced by the larger object, then the smaller object has a smaller magnitude buoyant force exerted on it.

Newton's first law applies to both objects, as they are stationary, and thus the forces acting on either object must sum to zero.
Since the smaller object has a small upwards buoyant force acting on it, then it must have a correspondingly small downwards weight force acting on it. Similarly, the larger object has a larger buoyant force and a larger weight force acting on it. Thus the larger object has a greater weight than the smaller object.

Sections 70854, 70855
Exam code: quiz05nWaW
(A) : 1 student
(B) : 32 students
(C) : 4 students
(D) : 12 students

Success level: 65%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.17

Physics quiz question: speed, pressure changes in horizontal, narrowing pipe

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA

Water as it moves horizontally from [1]→[2] through a pipe with decreasing cross-sectional area. The radius of the pipe at point [1] is 0.10 m, and water enters point [1] with a speed of 0.25 m/s. Assume ideal fluid flow. As water flows from [1]→[2], the speed __________; while the pressure __________.
(A) remains constant; remains constant.
(B) remains constant; changes.
(C) changes; remains constant.
(D) changes; changes.

Correct answer (highlight to unhide): (D)

From applying the continuity equation:

A1·v1 = A2·v2,

because the diameter of the pipe narrows as it flows from [1]→[2], the cross-sectional area decreases (A1 > A2), such that the speed of the water increases:

v1 < v2.

Then from Bernoulli's equation:

0 = ∆P + (1/2)·ρ·∆(v2) + ρ·g·∆y,

the third term on the right-hand side is zero because there is no change in elevation (y1 = y2), while the second term on the right-hand side increases (as the speed increases along the pipe), thus the pressure must decrease. Thus both speed and pressure change as water flows from [1]→[2] through this pipe.

Sections 70854, 70855
Exam code: quiz05nWaW
(A) : 0 students
(B) : 6 students
(C) : 6 students
(D) : 36 students

Success level: 73%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29

Astronomy current events question: dendritic furrow formation on Mars

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!)
Thomas Deane, "Winters on Mars Are Shaping the Red Planet's Landscape" (October 27, 2017)
tcd.ie/news_events/articles/winters-on-mars-are-shaping-the-red-planet-s-landscape/8305
Researchers proposed that carbon dioxide rapidly changing from solid to vapor causes various sand dune features on Mars, based on:
(A) laboratory experiments.
(B) reflected infrared light.
(C) analysis of released gases.
(D) similar features in the Mojave desert.
(E) computer simulations.

Correct answer: (A)

Student responses
Sections 70178, 70186
(A) : 23 students
(B) : 1 student
(C) : 6 students
(D) : 7 students
(E) : 5 students

Astronomy current events question: Proxima Centauri's cold dust belt

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!)
Guillem Anglada, Pedro J. Amado, Antxon Alberdi, Enrique Macias, Itziar de Gregorio-Monsalvo, and Richard Hook, "ALMA Discovers Cold Dust Around Nearest Star" (November 3, 2017)
eso.org/public/news/eso1735/
The Atacama Large Millimeter/submillimeter Array Observatory detected a dust belt surrounding the star Proxima Centauri, which may indicate the presence of:
(A) gravitational waves.
(B) cold dark matter.
(C) a white dwarf.
(D) multiple planets.
(E) artificial asteroids.

Correct answer: (D)

Student responses
Sections 70178, 70186
(A) : 1 student
(B) : 7 students
(C) : 2 students
(D) : 28 students
(E) : 4 students

Astronomy current events question: comet orbiting star KIC 3542116

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!)
Abby Abazorius, Alyssa Drake, Robert Massey, Rebecca Johnson, and Michele Johnson, "Citizen Scientist Spots Comet Tails Streaking Past Distant Star" (October 30, 2017)
ras.org.uk/news-and-press/3061-citizen-scientist-spots-comet-tails-streaking-past-distant-star
A comet orbiting the star KIC 3542116 was discovered by an online volunteer noticing slight decreases in light as it __________ its star.
(A) gravitationally pulled.
(B) escaped from.
(C) collided with.
(D) passed in front of.
(E) reflects light from.

Correct answer: (D)

Student responses
Sections 70178, 70186
(A) : 2 students
(B) : 0 students
(C) : 1 student
(D) : 37 students
(E) : 2 students

20171116

Astronomy quiz question: star cluster with white dwarfs

Astronomy 210 Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

A star cluster with white dwarfs would also have __________ at the same time.
(A) massive protostars.
(B) medium-mass main sequence stars.
(C) red dwarfs.
(D) giants.

Correct answer (highlight to unhide): (C)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Medium-mass stars start out as protostars, then reach their main sequence stage, and subsequently become giants, planetary nebulae, and then white dwarfs. So a star cluster with medium-mass stars in their terminal white dwarf stage would not have the earlier stages of medium-mass stars: main-sequence nor giants.

Since massive stars evolve from protostars much faster than medium-mass stars to reach their main-sequence stage, and then to become supergiants that explode as type II supernovae, none of them will be in their protostar stage in a star cluster where the medium-mass stars have already long ended their main-sequence lifetimes.

Low-mass stars evolve from protostars much slower than medium-mass stars to reach their main-sequence stage to become red dwarfs, and since these low-mass stars have such long main-sequence lifetimes (there have been no red dwarfs that have left the main-sequence since the universe began), and so low-mass red dwarfs can be found in an old star cluster where the medium-mass stars have reached their terminal white dwarf stage.

Section 70158
Exam code: quiz06sSu3
(A) : 5 students
(B) : 19 students
(C) : 9 students
(D) : 10 students

Success level: 25% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.31

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

Section 70158, version 1
Exam code: quiz06sSu3


Section 70158
0- 8.0 :   *** [low = 7.5]
8.5-16.0 :   ****************
16.5-24.0 :   ************ [mean = 19.3 +/- 8.0]
24.5-32.0 :   ******
32.5-40.0 :   **** [high = 36.5]


Section 70160, version 1
Exam code: quiz06nMuE


Section 70160
0- 8.0 :   * [low = 8.0]
8.5-16.0 :   ********
16.5-24.0 :   ******
24.5-32.0 :   ********* [mean = 23.7 +/- 9.0]
32.5-40.0 :   ********* [high = 36.5]

20171115

Astronomy quiz question: stellar evolution states in star cluster

Astronomy 210 Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

Medium-mass stars in a new star cluster will be in their __________ stage.
(A) protostar.
(B) red dwarf.
(C) white dwarf.
(D) supergiant.

Correct answer (highlight to unhide): (A)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Medium-mass stars start out as protostars, then reach their main sequence stage, and subsequently become giants, planetary nebulae, and then white dwarfs. So an old star cluster would have medium-mass stars in their white dwarf stage; and a young star cluster would have medium-mass stars still in their protostar stage.

(Reponse (B) is a low-mass star stage; response (D) is a massive star stage.)

Section 70160
Exam code: quiz06nMuE
(A) : 18 students
(B) : 6 students
(C) : 3 students
(D) : 3 students

Success level: 61% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64

Online reading assignment: the Milky Way (SLO campus)

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

Students have a 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.

The following questions were asked on reading textbook chapters and previewing presentations on the Milky Way's shape, size and composition and spiral arm structure and formation.


Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"Finding out what the Milky Way galaxy looks like and discovering where we are located in it."

"The perspective of our Milky Way was interesting to me. It's pretty wild that even though we have an incredible body of knowledge of our galaxy, we are still so limited and have only seen so far out/so many angles. Our milky way is cool enough as it is, knowing how much we have yet to learn is really cool."

"Just the Milky Way in general!"

"When I read about our location in the universe and try to wrap my head around it I start to get lost. It's interesting because it is explaining away some of the things I have trouble understanding."

"How giants pulsate and how this can be a way to measure distances to globular clusters."

"I really liked the comparison to when you're camping and can't tell if your hair is okay or not."

"That we know about dark matter because of the speed the inner and outer parts of a galaxy rotate at. This has been personally interesting because dark matter was one of those concepts I had a hard time wrapping my brain around but now I feel like I have a little bit more understanding of it."

"Dark matter has always been super-interesting to me, so it was nice to see it talked about."

"The fact that you can't see dark matter but it still exists."

"Dark matter. It's just so mysterious still, even when we know and have evidence of it's existence."

"The persistence of vision section was cool. I had seen things like that in the past, but it was cool to read how it works."

"That the most massive stars don't have the time to move from their place of birth. This makes sense, but I never realized it."

"The fact that the Milky Way impermanent and illusory and in a sense is also self-sustaining."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Nothing was particularly confusing other than the apparent reliance of a hypothetical person on a mirror for fixing their hair."

"The question about how much of the stars in our galaxy can be observed from Earth, because I couldn't find it in the presentation or the book."

"I have a problem imagining where things are supposed to be in space."

"Figuring out our position in the Milky Way. It's something I'd really like to focus on in class."

"What the halo is confuses me. I really don't get what it is."

"Dark matter. Specifically the halo and what it is made of."

"I found gravity and orbits within the Milky Way slightly confusing, I am having trouble distinguishing the two different motions."

"I have a tough time understanding dark matter and where its from and where it is in the universe. I am not fully understanding its origin."

"I don't know if I'm fully grasping the concept of spiral arms in our Milky Way. I think I get the main idea but I'm not entirely sure how it relates to us on earth. Also, how many of these arms does our Milky Way have? It looks like four on one of the diagrams but I'm not sure if that's solely meant to illustrate the concept or not."

"I'm not sure why the spiral arms on our galaxy don't actually move...can you go over the PimpStar Rims thing?"

"I don't really understand the spiral arms presentation very well. I'm having trouble with all of it. I don't really know what questions to ask."

"That spiral arms and spurs have two separate causes that form them. Why do density waves not also account for spurs?"

"Density waves/spiral arms. I get the just of it, but am still a bit confused on how they form."

"Straightforward!"

"For once I actually think I am not completely confused."

"I didn't find this too confusing compare to the last reading assignment. Then again I understand the topic a bit better right after your explanations."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?
As much as can be seen with the naked eye.  ************ [12]
Not very much.  ************* [13]
Barely seen it.  ***** [5]
(Never been able to see it.)  *** [3]
(Unsure/guessing/lost/help!)  * [1]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.
1%.  ******* [7]
5%.  ****** [6]
10%.  ********* [9]
50%.  **** [4]
100%.  [0]
(Unsure/guessing/lost/help!)  ******** [8]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?
"Look at your reflection in a stagnant pool of water or something shiny."

"Phone camera or app."

"You could use a metal spoon."

"Ask someone if you are camping together. (Or just don't worry about it.)"

"Well first of all, I would have a friend with me because camping alone sounds awful."

"You could ask a friend to draw you a picture."

"Hope for the best."

"I wouldn't care, I'm camping!"

"I have short hair, so this would not bother me."

"I would put on a beanie and worry no longer."

"It would not matter, I would throw it up in a ponytail and put a hat on. Because who cares! No need to impress anyone."

"You could look at your shadow on the ground to see if the outline of your hair looks messy."

"Feel it and try to feel the shape?"

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"They work by utilizing the persistence of vision illusion. This is done by coordinating the color of (or potentially turning on and off specific parts of the) lights on the wheels to make a pattern as they are spun at high speeds."

"The lights are hooked up to a computer that tells it when to light up and when not to, causing them to put off special images."

"The images are made with a strobe modulation technique."

"Rapidly blinking lights are coordinated to create patterns when swept across our field of vision."

"Using persistence of vision, coordinating the lights, when it is swept across our field of vision the picture appears. Just like when short-lived massive stars are born and die at certain intervals as they orbit around."

"Not sure."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"What is making the whole galaxy rotate in the first place? What's stopping everything from going past the boundaries and beyond?" (The Milky Way formed from a gigantic cloud of hydrogen that contracted over time; any rotation in the original cloud, no matter how slow, would just get faster as it the cloud got smaller to form the Milky Way.)

"Maybe our galaxy just has billions of Nibblers floating around producing 'dark matter' in our galaxy that causes this spread of gravity."

"What is dark matter made of?" (Nobody knows for sure, but there is a short list of suspects.)

"Do you really have a bike with 'PDOG' lights on the wheels? If so, that's awesome. How much did that setup cost you?" (That Schwinn Tire Writer was about $30-$40 or so; but they've been discontinued.)

"Talking about galaxies makes me feel small, as if talking about stars didn't already." (Then my job here is finished.)

"Are you ever sleepy during class? You always seem alert and I don't know how you do it." (You would be pretty enthusiastic too, if you had the opportunity to talk about the universe to astronomy students. #stoke)

"Could you describe your life using any one law of physics?" (Newton's first law: objects that are in motion tend to stay in motion. #keepmoving)

"Is it true that the last quiz is pretty much freebie points?" (Well, yes, if you show up for the last week of class and take the exit survey on how much you've learned about how stars work.)

"Do you like to go camping or glamping? Do you enjoy camping, if so what is your favorite spot?"(Mrs. P-dog and I probably do equal amounts of camping and glamping together. It's hard to pick a favorite spot, but earlier this year we did snag a great campsite at the Valley of Fire.)

"Happy Hanukkah." (Chag Urim Sameach! #toosoon)

Online reading assignment: waves

Physics 205A, fall semester 2017
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.

The following questions were asked on reading textbook chapters and previewing a presentation on waves.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Amplitude is the height between undisturbed position and the crest. It looks like the undisturbed position is in the middle of the wave. Mass divided by length is the linear density."

"For a transverse wave, the disturbance is sideways to the direction of the wave motion, and for a longitudinal wave, the disturbance is along the direction of the wave motion. I also learned about waves, for example, the speed of periodic waves along strings is set by the string tension and thickness, but the frequency of the wave is set by the source. The resulting spatial repeat interval is the wavelength."

"Wavelength depends on speed and frequency. Speed and frequency do not depend on wavelength. Transverse and longitudinal waves can both be periodic waves."

"Transverse waves flow up and down in one direction and longitudinal waves flow forwards-backwards in the same direction. The speed of waves weaken over time and depend on the medium of its flow."

"Again, this chapter was some nice review from what I learned in my high school physics class. I understand waves and the different types of them as well as how each wave differs in look and how to calculate various problems with given information about the waves."

"All waves are traveling disturbances and they all carry energy from one place to another. Two types of waves are longitudinal and transverse with one being where the disturbance is parallel to travel and the other is perpendicular."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"The difference in waves' motions with different frequencies confused me, also how the waves compare to others with the same speeds but different amplitudes. The formula applications are confusing also."

"I still don't fully understand how a sonic boom is created by a whip with its end moving fast enough to break the sound barrier."

"REVIEW REVIEW REVIEW. It makes sense conceptually, but it will really sink in with reviewing how to apply these concepts to problems. I think just learning how to apply these in the form of equations seems more difficult at home, but when in class it seems clear."

"This seems pretty straightforward... but is it?"

"I wasn't very confused on much, I have had some practice with waves."

A string of a given length has a certain linear mass density (mass/length) value. If this string is cut in half, then its linear mass density will:
decrease.   ********** [10]
remain constant.   ********************* [21]
increase.   *********** [11]
(Unsure/lost/guessing/help!)   [0]

The top and bottom waves have the same frequency, but different amplitudes. Identify which waves have the greater wave parameter.
(Only correct responses shown.)
Faster wave speed v: there is (approximately) a tie. [64%]
Longer wavelength λ: there is (approximately) a tie. [40%]

The top and bottom waves have the same amplitude, but different frequencies. Identify which waves have the greater wave parameter.
(Only correct responses shown.)
Faster wave speed v: there is (approximately) a tie. [38%]
Longer wavelength λ: top wave (low frequency f). [93%]

This wave travels from the left section to the right section of this apparatus. Identify along which section the waves have the greater wave parameter.
(Only correct responses shown.)
Faster wave speed v: Along the right apparatus. [36%]
Longer wavelength λ: along the right apparatus. [86%]
Higher frequency f: there is (approximately) a tie. [19%]

For transverse waves on a string, classify each of these parameters are being "independent" (able to be changed without affecting other independent parameters), or "dependent" (will be changed when independent values are changed).
(Only correct responses shown.)
Amplitude A: independent. [62%]
Wave speed v: independent. [52%]
Frequency f: independent. [55%]
Wavelength λ: dependent. [81%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are the wave parameters just amplitude, speed, frequency, and wavelength?" (Yes. Although the list looks simple, the relationships between them (independent and dependent) are pretty complicated.)

"Some brief review with numbers would be good for class!" (We have time for that.)

"If we have time, I would be stoked if you could do a little run through the basics/general ideas/key points of this presentation in the next class period. Thanks!"

"Have you seen Kelly Slater's perfect wave pool? It's pretty neat." (And it's in Lemoore, CA, which basically just up Highway 41!)

20171114

Online reading assignment: the Milky Way (NC campus)

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

Students have a 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.

The following questions were asked on reading textbook chapters and previewing presentations on the Milky Way's shape, size and composition and spiral arm structure and formation.


Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"The sheer amount of predicted stars in our galaxy is interesting because among all of there must be one that is completely unique in every way, something so insane that we couldn't begin to understand it."

"I have always wondered how scientists can describe the shape of the galaxy we live in so it was interesting to read about how it is known."

"I found the different methods of mentally visualizing our galaxy very interesting. Obviously since the galaxy is so massive and we cannot view ourselves and only others it is interesting that we can base what our galaxy looks like off of these particular methods."

"The fact that we have only recently discovered that we are not in the center of the galaxy. And I love that the word 'galaxy' is a derivative of 'milk.'"

"I thought it was super fascinating how the only stars we see that are from our galaxy are located in a stream across the sky. I know that may sound basic, but too me that is super cool."

"I think that all of the ways that we can use to map our galaxy is kind of cool."

"I enjoyed learning about dark matter and how the difference in rotations of galaxies can give you info on how much mass/gravity is spread out through the galaxy."

"Something I found interesting from the presentation previews was that stars in our Milky Way orbit at the same speed in the outer and inner layers of our galaxy. I found this interesting because I didn't know that dark matter is what made this happen."

"I thought it was really cool to learn that there are different formations of stars in certain areas of the Milky Way. Type II supernovae create new star formations in the spurs and pulling in and colliding with dwarf galaxies creates them in the arms. This was cool because before this class I thought stars were all made the same way, and before this section I didn't think there would be much differentiation depending on where they were located within a galaxy."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
Something confusing to me was the mass of the galaxy. How did people back than have capability when trying to figure out an estimated measurement? What was needed to figure out the accurate results for the mass of the galaxy?"

"Global cluster positions."

"Can spacetime curvature be manipulated? Are planets, black hole, stars etc the only ones that can do this?"

"I am not quite sure why the spiral arms exist at all. What does the presence of spiral arms say about a galaxy's nature or surroundings?"

"I still don't really understand how exactly the Milky Way pulls in dwarf galaxies. I'm assuming it (obviously) has something to do with gravity, but I would like to know more about the how and why."

"I did not understand the section on what would initiate a density wave in the Milky Way and how that related to the traffic jam example."

"With density waves, how long, in general, do they take to 'smooth out?'"

"I found the motion of and the speed of 'traffic jams' in the presentation presentation a bit confusing."

"Persistence of vision."

"othing was particularly confusing. How can we know the shape of the Milky Way when we are in it?"

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?
As much as can be seen with the naked eye.  *********** [11]
Not very much.  ******** [9]
Barely seen it.  *** [3]
(Never been able to see it.)  * [1]
(Unsure/guessing/lost/help!)  * [1]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.
1%.  ***** [5]
5%.  ****** [6]
10%.  ******* [7]
50%.  ***** [5]
100%.  [0]
(Unsure/guessing/lost/help!)  ** [2]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?
"By using what's around you, such as water to see your reflection."

"Have a friend tell me, one who I knew would be brutally honest with me."

"You could look at yourself with your phone."

"Look around your peripheral view to see if any hair is sticking out."

"I would probably feel out the parting in my hair and pat it down after parting it. My hair is quite simple so I really don’t need to do much with it."

"STEP 1: Lift one hand into the air. STEP 2: Quickly place hand onto head. STEP 3: Take a chill pill."

"I would just wear a beanie the whole time. Problem solved."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"A microprocesser tells what light to be on or off and what color to be at a certain time while its rotating around the rim."

"Both of these examples are spinning LED lights that blink while they are moving to create patterns. It is called the persistence of vision."

"They work because as the wheel goes around, something triggers the lights (just as gas and dust trigger star formations, causing a traffic jam), and then they go off again as the trigger relaxes."

"Like they said, 'voodoo.'"

"Not sure."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do you want to pimp out your car wheels with LEDs P-dog?"

"Can you please explain the PimpStar wheel system some more?"

"I found that the PimpStar rim analogy to be very useful."

"Where do I buy these rims?"

"I think I'll put some of those rims on my Prius...really spice it up."

"I like your rims on your bike, they are pretty cool!"

"Do you even bike at night, bro? With a sweet set-up like that you have to bike at night!"

"Please discuss more of dark matter! Thank you."

"Are we having another midterm?" (Yes, after Thanksgiving week.)

20171113

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz05nWaW



Sections 70854, 70855 results
0- 6 :  
7-12 :   ***** [low = 9]
13-18 :   ***************
19-24 :   ********************* [mean = 19.7 +/- 4.8]
25-30 :   ***** [high = 27]

Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2017
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.

The following questions were asked on reading textbook chapters and previewing a presentation on simple harmonic motion.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Simple harmonic motion is when the outside work on the object is being ignored, and under this ideal condition the back and forth motion of the object will continue forever."

"I felt like I got a solid grasp of the total energy conservation problems after reading the assigned material and looking over the blog."

"The further an object is from the origin the higher the elastic potential energy and vice versa for the kinetic energy."

"From the presentation, I understand the concept of total energy conservation. This models the previous conservation equations we've covered, and so it makes sense that energy must be conserved and one value must always consistently equal the other side of the equation. I understand how a spring can have kinetic energy (depending from where you start measuring it), as well as potential energy."

"An ideal spring is Fspring = –k·x and has no weight. Frequency is the number of cycles per second."

"In harmonic motion (uniform, symmetric oscillations) energy is transferred between KEtr and PEelas in a period matching the symmetric oscillation. Pendulums with a mass at one end vary in period depending on length of string. For a spring loaded with a mass, the mass determines period. However, the spring constant can weaken over time."

"The thing that I found most interesting and the thing that I understand the best from the assigned reading assignment was the pendulum part."

"A mass on a spring undergoing simple harmonic motion will have a constant total mechanical energy E. For a simple pendulum, the period depends on the square root of the string length L and the gravitational acceleration g."

"This section feels more challenging. I understand that as mass of a load increases, time for a spring or swing to go through a complete cycle is greater. I understand the components of the equations and the application of the equations."

"Honestly, I didn't get to this (yet)."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"I need the simple pendulum period explained, I can't understand how the book explains it."

"I'm not completely getting the mass on the spring and when it talks about translational kinetic energy and elastic potential energy. When one is zero, where is the other energy?"

"I am struggling with the total energy conservation equation."

"I think I need more clarification on energy conservation through the mass-spring concept."

"For now, everything else is confusing. I have a hard time comparing something increasing and decreasing. However when it remains constant, it is easier to make sense of the situation."

"I found the pendulum confusing. I don't really understand how its period work."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:
origin (x = 0).   ***** [5]
turnaround points (x = ±A).   ********************************* [33]
(Both of the above choices.)   ***** [5]
(Neither of the above choices.)   * [1]
(Unsure/lost/guessing/help!)   [0]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:
origin (x = 0).   **************************** [28]
turnaround points (x = ±A).   ********* [9]
(Both of the above choices.)   **** [4]
(Neither of the above choices.)   ** [2]
(Unsure/lost/guessing/help!)   * [1]

For these identical mass billiard balls hanging from strings of different lengths, the billiard balls hanging from shorter length strings have periods that are _________ the periods of the billiard balls hanging from longer length strings.
shorter than.   ************************************* [37]
equal to.   ****** [6]
longer than.   [0]
(Unsure/lost/guessing/help!)   * [1]

For the different mass riders on swings of the same lengths, the more massive rider has a period __________ the period of the less massive rider.
shorter than.   ******** [8]
equal to.   ************ [12]
longer than.   ************************ [24]
(Unsure/lost/guessing/help!)   [0]

For the overloaded truck with a vertical oscillation period of approximately half a second, after dumping its load (thus decreasing the mass connected to the springs in its suspension) would __________ the period of oscillation.
decrease.   ************************ [24]
have no affect on.   **** [4]
increase.   ************* [13]
(Unsure/lost/guessing/help!)   *** [3]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.
decrease.   ************* [13]
have no affect on.   **** [4]
increase.   ************************** [26]
(Unsure/lost/guessing/help!)   * [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I don't really understand simple harmonic motion and amplitude. A is amplitude, correct?" (Yes.)

"I think I understand this section. The reading was a little tough but your blog helped me understand it better."

"I have learned that I’m more of a visual learner so I could use a visual on how the formulas work. I get that the sum of the two energies has to equal the total mechanical energy, but just some overview would be great."

"Brief review on different mass pendulum problems would be great. When mass increases on a pendulum, would the period increase?" (No.)

"Very unsure about the weakening spring example above, but my inclination tells me the oscillation period would decrease."

"What is the spring constant k?" (It's a measure of how "strong" a spring is, in N/m. So a very weak spring might need only 0.001 N to stretch it by 1 m, while a very strong spring would need 1,000 N to stretch it by 1 m.")

"I could use more examples just to clarify. I think once we practice it in class, I will more clearly understand."

"I don't get what happens as the springs weaken over time."

"Please go over the questions from the second half of the presentation!"

"I'm a little confused by the decreasing the mass of an overload truck equation. it seems that it doesn't directly apply to either equation because it is a different kind of motion."

"Mostly how to do problems of frequency. Are we always expected to assume a spring is ideal?" (You should always be told whether a spring is ideal (or not).)

"I am still very much enjoying your class!"

20171110

Astronomy current events question: origin of object A/2017 U1

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!)
DC Agle, Laurie Cantillo, Dwayne Brown, and Roy Gal, "Small Asteroid or Comet 'Visits' from Beyond the Solar System" (October 26, 2017)
nasa.gov/feature/jpl/small-asteroid-or-comet-visits-from-beyond-the-solar-system
Based on observations of its trajectory, A/2017 U1 may be an asteroid or comet that is:
(A) from outside the solar system.
(B) made of dark matter.
(C) a neutron star remnant.
(D) propelled by gravity waves.
(E) nearly pure water ice.

Correct answer: (A)

Student responses
Sections 70178, 70186
(A) : 39 students
(B) : 2 students
(C) : 1 student
(D) : 1 student
(E) : 3 students

Astronomy current events question: Ceres' ocean remnants?

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!)
Elyssia Widjaja, "Dawn Finds Possible Ancient Ocean Remnants at Ceres" (October 26, 2017)
nasa.gov/feature/jpl/dawn-finds-possible-ancient-ocean-remnants-at-ceres
NASA's Dawn spacecraft's observations of __________ indicate that the dwarf planet Ceres may have had an ocean in the past.
(A) released gases.
(B) ongoing volcanic eruptions.
(C) infrared heat sources.
(D) subduction zones.
(E) smooth surface features.

Correct answer: (E)

Student responses
Section 70186
(A) : 5 students
(B) : 2 students
(C) : 3 students
(D) : 4 students
(E) : 7 students

Astronomy current events question: electrical hazards on Phobos, Deimos?

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!)
Bill Steigerwald, Nancy Jones, "Solar Eruptions Could Electrify Martian Moons" (October 18, 2017)
nasa.gov/press-release/goddard/2017/mars-electric-moons
Future rover or astronaut missions to Mars' moons Phobos and Deimos may encounter hazardous electrical conditions caused by:
(A) radioactivity.
(B) Mars' magnetic field.
(C) micrometeorite erosion.
(D) the solar wind.
(E) tidal heating.

Correct answer: (D)

Student responses
Sections 70178, 70186
(A) : 3 students
(B) : 2 students
(C) : 7 students
(D) : 34 students
(E) : 0 students

20171108

Online reading assignment: medium-mass stars, massive stars, neutron stars and black holes (SLO campus)

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

Students have a 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.

The following questions were asked on reading textbook chapters and previewing presentations on the evolution of medium-mass stars, massive stars, neutron stars and black holes.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"I enjoyed the metaphor comparing cars to stars in regards to life span and mileage. I think that it's interesting that those two vehicles have the same range of fuel, because it's not something you would expect from their appearance."

"A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. I never took into account the different sizes of the fuel tank only the vast differences of gas mileage."

"It's pretty interesting that no low-mass stars have died yet."

"I found the lifespan of the different kinds of stars pretty interesting because the low mass stars never die."

"Even though the universe has been around for many years I find it fascinating that low mass stars are still out there even though in my mind they should extinct."

"I found interesting was discovering that bigger stars have a shorter time span. You would think that larger stars would live longer since they are so big."

"Something I found interesting,is that the sun will eventually burn through its resources and kill off Earth which I never knew."

"I thought it was interesting that helium can only fuse into heavier elements at a temperature of 100,000,000 K. But no core of any main sequence star can even get that hot, so the helium hangs out in the center of the star."

"It's crazy to think the white dwarf kind of sucks the life out of its companion star, enough to where it kills them both *explodes into the abyss*"

"How the dropping of a basketball and tennis ball at the right time can mimic the explosion of a supernova."

"A lot of the imagery used in the presentations to illustrate a black hole was interesting, engaging, and helpful."

"The end of life cycle for a star makes sense now. I didn't fully understand how it ended."

"The death of the sun--obviously it's a bit depressing to think about but the process itself, including eventually vaporizing the earth is fascinating. It's probably more fascinating knowing that it won't happen during my lifetime, otherwise it would be horrifying. The death of stars in general is interesting and the fact that our sun shares that fate is just a powerful thing to think about."

"It's interesting that when a star can no longer use it's energy and support the crushing gravity it freaks out and its outer layers spaz out and blow up off the imploding core."

"I thought it was interesting that a black hole can actually go on forever and the fact that they can actually warp space. Truly mind-blowing."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Also how low-mass stars have not died yet, it's interesting and confusing. How long have they been there? Are they all from the same star cluster, or did they start out on their own? Can anything be learned about the universe from them? So many questions!"

"How do we know that no low mass stars haven't expired yet? Maybe they have and just didn't leave a trace of their existence."

"I'm confused about the low mass stars. What happens when they die? Do they even die?"

"The end of life stages were hard to grasp because it didn't feel like the masses of the stars were explicitly mentioned and so it was just overall confusing to me."

"During helium fusion of a star, does the star actually grow in size? If not, how does it expand."

"Right now, pretty much everything is a little confusing. It was a lot of information to take in."

"I still don't get why a neutron star creates pulsars and the more I read about all the actions of dying stars the more I get confused. the book makes things pretty complex."

"Something that was a bit confusing were the different types of supernova explosions and what exactly makes them different. As well as what differentiates a regular nova from a supernova."

"In general, supernovas are a bit hard to wrap my head around."

"Black holes are still a little confusing for me."

"I don't understand how black holes bend space time. I think this is so confusing because don't quite understand what spacetime is."

"Time dilation has me very confused."

A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. Briefly explain how this is possible.
"The smart car is small and has a small tank of gas. The H2 is big and has a large tank of gas. Their fuel capacity/mileage ratios are reverse of one another. They go the same distance."

"Even if the SmartCar has better mileage it has a smaller tank, the Hummer has less mileage but it has a bigger tank."

"The Hummer H2 has a larger gas tank but has less mpg than the SmartCar ForTwo. However, the Smartcar has a smaller gas tank, but has greater mpg than the Hummer, so in turn they will travel the same distance with a full tank of gas."

Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)
Black hole: massive main sequence star [86%]
Neutron star: massive main sequence star [51%]
White dwarf: medium-mass main-sequence star [59%]
(No stellar remnant observed yet: low-mass main-sequence star [59%]

Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)
Type II supernova: massive main sequence star: [84%]
Type Ia supernova: medium-mass main-sequence star [73%]
Nova: medium-mass main-sequence star [49%]
Low-mass main-sequence star: (no explosion possible) [62%]

If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.
seconds.  ** [2]
hours.  [0]
days.  [0]
a year.  [0]
many years.  ***** [5]
forever.  ************************* [25]
(Unsure/guessing/lost/help!)  ***** [5]

The first rule of astronomy class is...
"Study."

"Go to class."

"Create a study group."

"Pay attention. Show up? Look up? Is this a trick?"

"Look to the stars to find the answers you seek...about stars."

"To make intelligent hypothetical theories and to use the scientific method to study the physics of stars and outer space, from moons to black holes; an educated scientific hypothesis is very important, and some say it's necessary to getting a good grade"

"Eat a meal before you come to class."

"Come to class fully caffeinated and ready to learn."

"Wait, I thought this was astrology..."

"Don't look at the sun through a telescope."

"Talk with everyone about astronomy class."

"Do not talk about astronomy class."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"What made you decide on doing a three hour class? In both lab and lecture?" (All science labs at Cuesta College are three hours long. The three hour lecture is because it's hard enough to get students to come to campus one night a week.)

"Could you please explain white dwarfs in the next class, I was confused with white dwarfs, thank you."

"A little confused by this weeks presentations so I'm looking forward to hearing you go over them."

"Please go over the different types of explosions. Thanks!"

"Can you 'dumb' this section down?" (Eh, I'm going to smart you up.)

"Are we ever going to see a picture of Mrs. P-dog?" (Didn't I show you a picture of us in the first week of class? Eh, here's another pic.)

"Is Fight Club one of your favorite movies?" (Sir, is this a test?)

"What's the first rule of astronomy class?"