20171130

Astronomy current events question: pulsar timing detection of gravitational waves?

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!)
News release, "Gravitational Waves from Merging Supermassive Black Holes Will Be Spotted within 10 Years, New Study Predicts" (November 13, 2017)
simonsfoundation.org/2017/11/13/gravitational-waves-supermassive-black-hole-merger/
Computer simulations predict that gravitational waves from merging supermassive black holes could be detected by monitoring variations in:
(A) matter-antimatter production.
(B) dark matter densities.
(C) pulsar times.
(D) radioactive decay rates.
(E) type II supernova brightnesses.

Correct answer: (C)

Student responses
Sections 70178, 70186
(A) : 3 students
(B) : 6 students
(C) : 29 students
(D) : 4 students
(E) : 1 student

Astronomy current events question: ADFS-27 galaxy pair rapid star formation

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!)
News release, "Duo of Titanic Galaxies Captured in Extreme Starbursting Merger" (November 13, 2017)
public.nrao.edu/news/2017-alma-starbursting-merger/
The Atacama Large Millimeter/submillimeter Array (ALMA) observed ADFS-27, a pair of galaxies with rapid star formation triggered by:
(A) merging supermassive black holes.
(B) the end of the big bang.
(C) matter-antimatter annihilation.
(D) passing through each other.
(E) type II supernova explosions.

Correct answer: (D)

Student responses
Sections 70178, 70186
(A) : 22 students
(B) : 1 student
(C) : 3 students
(D) : 12 students
(E) : 4 students

Astronomy current events question: exoplanet Ross 128 b orbiting quiet red dwarf star

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!)
Xavier Bonfils, Nicola Astudillo-Defru, and Richard Hook, "Closest Temperate World Orbiting Quiet Star Discovered" (November 15, 2017)
eso.org/public/news/eso1736/
Exoplanet Ross 128 b is considered to be more likely to sustain life than Proxima b, as Ross 128 b orbits a red dwarf that has:
(A) quieter flare activity.
(B) stronger magnetic fields.
(C) more gravity.
(D) more metals.
(E) a cooler habitable zone.

Correct answer: (A)

Student responses
Sections 70178, 70186
(A) : 17 students
(B) : 2 students
(C) : 3 students
(D) : 1 student
(E) : 15 students

20171128

Physics quiz question: concrete sample compression

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

A concrete sample was (non-destructively) tested by compressing it with a stress of 9.9×106 N/m2[*]. The Young's modulus of this concrete is 2.8×1010 N/m2[**]. If the concrete sample started with a height of 0.305 m, during testing it was compressed by:
(A) 1.1×10–11 m.
(B) 1.1×10–4 m.
(C) 3.5×10–4 m.
(D) 5.5×10–3 m.

[*] youtu.be/iCWsDHhbi9g.
[**] engineeringtoolbox.com/concrete-properties-d_1223.html.

Correct answer (highlight to unhide): (B)

Hooke's law is given by:

(F/A) = Y·(∆L/L),

where the compressive stress (F/A) is given as 9.9×106 N/m2. The amount that sample would be compressed by will be:

L = (F/A)·(L/Y),

L = (9.9×106 N/m2)·((0.305 m)/(2.8×1010 N/m2)),

L = 0.0001078392857 m,

or to two significant figures, the concrete sample would compress by 1.1×10–4 m.

(Response (A) is L/Y; response (C) is the strain (∆L/L) = (F/A)/Y; response (D) is the volume of the concrete cylinder, which cannot be determined from the values given above.)

Sections 70854, 70855
Exam code: quiz06Ho0k
(A) : 4 students
(B) : 40 students
(C) : 1 student
(D) : 0 students

Success level: 89%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27

Physics quiz question: energy stored in compressed spring

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

A replacement coil spring for a Lincoln Town Car[*] has a spring constant of 740 N/m, and is mounted such that it can be compressed horizontally. When this spring is compressed by 0.020 m, it stores __________ of elastic potential energy.
(A) 0.15 J.
(B) 0.30 J.
(C) 7.4 J.
(D) 15 J.

[*] streetsideauto.com/p/moog-9114/

Correct answer (highlight to unhide): (A)

The change in elastic potential energy is given by:

PEelas = (1/2)·k·∆(x2) = (1/2)·k·(xf2x02),

where the spring was initially uncompressed (x0 = 0) and then compressed by xf = –0.020 m from equilibrium, such that:

PEelas = (1/2)·(740 N/m)·((–0.020 m)2 – (0)2) = 0.148 J,

or to two significant figures, the spring stores 0.15 J of elastic potential energy.

(Response (B) is k·xf2; response (C) is (1/2)·k·xf; response (D) is k·xf, which is the force required to compress the spring by 0.020 m.)

Sections 70854, 70855
Exam code: quiz06Ho0k
(A) : 27 students
(B) : 1 student
(C) : 5 students
(D) : 12 students

Success level: 60%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73

Physics quiz question: comparison of mass-spring periods

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

A mass of 0.100 kg hangs from a k = 10.0 N/m spring, while a mass of 2.20 kg hangs from a k = 200.0 N/m spring[*][**]. The __________ system will have a longer oscillation period.
(A) 0.100 kg mass, 10.0 N/m spring.
(B) 2.20 kg mass, 200.0 N/m spring.
(C) (There is a tie.)
(D) (Not enough information is given.)

[*] eiscolabs.com/products/ph0323ss?variant=6635998660.
[**] google.com/shopping/product/3295840510445490103.

Correct answer (highlight to unhide): (B)

The period T of a mass m attached to a spring with spring constant k is given by:

T = 2·π·√(m/k).

For the 0.100 kg mass, 10.0 N/m spring system, the period is:

T = 2·π·√((0.100 kg)/(10.0 N/m)) = 0.6283185307 s,

or to three significant figures, 0.628 s.

For the 2.20 kg mass, 200.0 N/m spring system, the period is:

T = 2·π·√((2.20 kg)/(200.0 N/m)) = 0.6589860345 s,

or to three significant figures, 0.659 s.

Thus the 2.20 kg mass, 200.0 N/m spring system will have a longer oscillation period than the 0.100 kg mass, 10.0 N/m spring system.

Sections 70854, 70855
Exam code: quiz06Ho0k
(A) : 6 students
(B) : 38 students
(C) : 1 student
(D) : 0 students

Success level: 84%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36

Physics quiz question: finding acceleration due to gravity from pendulum period

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

A "seconds pendulum" is defined to be a pendulum with a period of exactly two seconds[*]. The length of string used to construct this pendulum at the equator was measured to be 0.99065 m during an expedition in 1735[**]. Based on this result, the magnitude of the acceleration due to gravity g at the equator in 1735 was:
(A) 9.6859 m/s2.
(B) 9.7773 m/s2.
(C) 9.8696 m/s2.
(D) 9.9628 m/s2.

[*] wki.pe/Seconds_pendulum.
[**] Michael R. Matthews, Time for Science Education: How Teaching the History and Philosophy of Pendulum Motion Can Contribute to Science Literacy, Springer Science & Business Media (2000), p. 147.

Correct answer (highlight to unhide): (B)

The period of a pendulum is given by:

T = 2·π·√(L/g),

Since the period T = 2 s and string length L = 0.99065 m are known, the acceleration due to gravity g can then be solved for:

g = L·((2·π)/T)2,

g = (0.99065 m)·((2·π)/(2 s)/)2 = 9.7773235999  m/s2,

or to five significant figures, the acceleration due to gravity is 9.7773 m/s2.

(Response (A) is (π·L)2; response (C) is π2); response (D) is π2/L.)

Sections 70854, 70855
Exam code: quiz06Ho0k
(A) : 1 student
(B) : 34 students
(C) : 7 students
(D) : 3 students

Success level: 76%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.82

Physics quiz question: increasing string tension

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA

"Strings [44|365]"
Gala Medina
flic.kr/p/9hXzj1

A C3 piano string[*] has a linear mass density of 10.8 g/m, and is stretched with a tension of 747 N. Increasing the tension would __________ the speed of transverse waves along this string.
(A) decrease.
(B) not change.
(C) increase.
(D) (Not enough information is given.)

[*] A. Stulov, "Physical Modelling of the Piano String Scale," Applied Acoustics, vol. 69 (2008) pp. 977–984, cs.ioc.ee/~stulov/appl08.pdf.

Correct answer (highlight to unhide): (C)

The speed v of transverse waves along the piano string depends on the tension F and the linear mass density (mass per unit length) (m/L):

v = √(F/(m/L)).

Thus increasing the tension F in the piano string would increase the wave speed (but would also not affect the linear mass density).

Sections 70854, 70855
Exam code: quiz06Ho0k
(A) : 1 student
(B) : 12 students
(C) : 32 students
(D) : 0 students

Success level: 71%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73

20171122

Physics quiz archive: simple harmonic motion, waves

Physics 205A Quiz 6, fall semester 2017
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855 version 1
Exam code: quiz06Ho0k


Sections 70854, 70855 results
0- 6 :   * [low = 6]
7-12 :   *
13-18 :   *********
19-24 :   ************* [mean = 23.3 +/- 5.8]
25-30 :   ********************* [high = 30]

Online reading assignment: temperature

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 temperature.


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.
"The increase in any one dimension of a solid is called linear expansion. The volume of a normal material also increases as temperature increases, this is known as volume thermal expansion."

"The material-dependent linear expansion coefficient characterizes the response of the material to thermal stress."

"The material in the section relate to experiences in real life, such as liquid expanding when it is cooled and metals cooling and expanding."

"Solids and liquids expand with changes in temperature. A shorter length rod will expand less than a longer length when made of the same material and same change in temperature. ∆L is the change in length due to temperature."

"Thermal stress causes strain. A shorter beam will require a greater change in temperature to expand/contract the same distance as a longer beam."

"I learned that I need cooler gas to save money at the pump."

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 don't fully understand volume expansion and feel that in some of the equations I would go go back and forth on what increases or decreases in volume."

"I found thermal stress and strain confusing. I could use further explanation on the equation."

"How you would calculate the amount of expansion that a metal undergoes by given the original length and the temperature?"

"I do not know how all of the equations relate to each other. I think I will have to review more before next class."

"Not as confusing as the last few subjects. Which is a relief for the end of semester. Still, I skimmed it because I'm studying for the quiz."

"Could you go over thermal stress? Maybe do an example problem, the one in the book was a little confusing."

"I didn't understand why the shorter beam will require a greater increase in temperature to expand the same amount as the longer beam."

"Thankfully due to my chemistry class this wasn't very confusing."

"I found most everything confusing from this reading and would benefit greatly from in class examples."

"I haven't gotten much into the reading yet, so it's all a little confusing right now."

"Nothing."

For solids, what is the mathematical relationship between the coefficient of volume expansion β and the coefficient of linear expansion α?
"β = 3·α."

"They have the same units, K–1."

"No idea."

To expand these two steel beams 1.0 cm from their original lengths, the longer beam will require __________ temperature increase compared to the shorter beam.
a smaller.  *********************** [23]
the same.  **** [4]
a larger.  ****** [6]
(Unsure/guessing/lost/help!)  * [1]

For a thermometer, the glass volume expansion coefficient 3αglass is __________ the alcohol volume expansion coefficient βalcohol.
less than.  ********************** [22]
equal to.  ***** [5]
greater than.  ***** [5]
(Unsure/guessing/lost/help!)  ** [2]

For the water level in this plastic rainwater basin to lower as the temperature falls overnight, the plastic volume expansion coefficient 3αplastic must be __________ the water volume expansion coefficient βwater.
less than.  ************* [13]
equal to.  **** [4]
greater than.  ************ [12]
(Unsure/guessing/lost/help!)  ***** [5]

A certain fuel company will measure out a gallon of gasoline and sell it for the same price, whether it is cool or warm. Indicate the gallon of gasoline that has a greater:
(Only correct responses shown.)
mass: the cool gallon [38%]
density: the cool gallon [68%]

Briefly explain why a gallon of gasoline purchased when it is cool would be better than a gallon of gasoline purchased when it is warm. (In either case, the fuel company dispenses the same volume of exactly one "standard" gallon.)
"I don't know. Is it easier to handle? Maybe cheaper to move."

"The cooler gallon of gasoline would have more density and therefore should have more energy based in that gallon of gasoline."

"Because it has a greater density so the amount of energy within that gallon of gasoline is greater."

"The gasoline is more dense when it is cold and there for the volume is smaller. Although when it is warm the volume is bigger due to it being less dense. The volume might be more but the amount is still the same. Gas stations measure by volume therefore it is better to get gas when it is cold."

"Gasoline (and nearly all objects) expand and become less dense due to heat. Because of this it is more dense during a cool day. Since its density increases and since gas is bought in volume, you get more 'bang for your buck' when you buy on a cooler day."

"How can we figure out the gasoline question? We weren't given the properties of gasoline and how reactive it is at different temperatures."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Thank you for applying concepts to real-life situations."

"Does heat by itself change the atomic structure in solids?" (The space between atoms increases as atoms vibrate more at higher temperatures, because atoms repel each other at close distances, they will spend more time farther apart than closer together as they vibrate more.)

"We will soon be fluent in Greek." (Graecum est; non legitur.)

"Still really enjoying the class."

20171121

Astronomy current events question: "repeating" supernova iPTF14hls

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!)
Sandy Seale, "Las Cumbres Astronomers Discover a Star That Would Not Die" (November 2, 2017)
lco.global/news/las-cumbres-astronomers-discover-a-star-that-would-not-die/
Researchers proposed that the supernova iPTF14hls has been able to explode several times over the past 50 years by being hot enough to produce __________ in its core.
(A) matter and antimatter.
(B) dark matter.
(C) radioactive isotopes.
(D) spacetime instabilities.
(E) gravitational waves.

Correct answer: (A)

Student responses
Sections 70178, 70186
(A) : 22 students
(B) : 4 students
(C) : 9 students
(D) : 0 students
(E) : 3 students

Astronomy current events question: discovery of OGLE-2016-BLG-1190Lb

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!)
Tomasz Nowakowski, "Extremely Massive Exoplanet Discovered in the Milky Way's Bulge" (November 6, 2017)
phys.org/news/2017-11-extremely-massive-exoplanet-milky-bulge.html
The extremely massive planet OGLE-2016-BLG-1190Lb orbiting a white dwarf was discovered by NASA's Spitzer Space Telescope observations of how their __________ distorted light from a background star.
(A) magnetic fields.
(B) deuterium fusion.
(C) pulsar beams.
(D) nova explosions.
(E) gravity.

Correct answer: (E)

Student responses
Sections 70178, 70186
(A) : 9 students
(B) : 9 students
(C) : 5 students
(D) : 2 students
(E) : 14 students

Astronomy current events question: Chicxulub impact site hydrocarbon soot?

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!)
Kunio Kaiho and Naga Oshima, "Site of Asteroid Impact Changed the History of Life" (November 10, 2017)
tohoku.ac.jp/en/press/asteroid_impact.html
Researchers proposed that the Chicxulub asteroid may not have caused the extinction of dinosaurs if its impact area had been hydrocarbon-poor, based on:
(A) laboratory experiments. (B) fossil carbon dating. (C) analysis of trapped gases. (D) tree ring spacings. (E) computer models.

Correct answer: (E)

Student responses
Sections 70178, 70186
(A) : 7 students
(B) : 7 students
(C) : 17 students
(D) : 0 students
(E) : 7 students

20171120

Online reading assignment: standing 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.
"Wavelength is dependent on speed and frequency. Fundamental frequency is dependent on wave speed and length. Changing the independent variables changes the dependent variables."

"Again, this is some very nice review of what I learned in high school physics. The concept of waves, periods, and frequency all make sense to me. As well as the way in which they are applied in both physics problems and everyday life."

"The speed, frequency, and amplitude of a wave are independent and can be changed without affecting each other, but wavelength is affected by speed and frequency. Natural frequency is when resonance occurs and if the string is vibrated twice the frequency, the string creates a second harmonic, a third for three and so on."

"Guitar or bass strings that are thicker resonate at a lower fundamentals frequency than thinner strings. This is because of the relationship of mass per length. A thicker string would have more mass meaning that the frequency would have to be lower if the mass was higher."

"Strings of finite length, when disturbed with a period in their fundamental frequency, experience a property called resonance. Different string thicknesses have different fundamental frequencies, which explains how plucking guitar strings makes different sounds. Fundamental frequencies are also affected by string length."

"If a string were to be plucked, it would oscillate at its fundamental frequency. If a string were periodically disturbed at the same fundamental frequency, then it would undergo resonance instead. Then if a string were oscillated at twice the fundamental frequency, then it would result in a pattern that creates a node in the center which is where we get the 'standing' in standing waves."

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'm still a little confused when the wave string speed equation and when to use the independent parameters equation when simply determining what is and isn't changing."

"I had some trouble with 'standing waves.' Could you go over this?"

"More elaboration on resonance."

"Nothing."

"I did not find anything confusing."

(Assuming that their tensions are approximately equal), the __________ strings have a slower wave speed.
thicker.   *********************************** [35]
thinner.   ** [2]
(There is a tie.)   *** [3]
(Unsure/lost/guessing/help!)   ** [2]

After these same-length guitar strings are plucked (assuming that their tensions are approximately equal), the __________ strings vibrate at a lower fundamental frequency.
thicker.   **************************** [28]
thinner.   **** [4]
(There is a tie.)   ****** [6]
(Unsure/lost/guessing/help!)   **** [4]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the speed of waves along the string.
decrease.   ******* [7]
not change.   **************** [16]
increase.   ***************** [17]
(Unsure/lost/guessing/help!)   ** [2]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the fundamental frequency of the string.
decrease.   ************ [12]
not change.   ******** [8]
increase.   ***** [20]
(Unsure/lost/guessing/help!)   ** [2]

For standing 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.)
Wave speed v: independent [50%]
String length L: independent. [62%]
Fundamental frequency f1: dependent. [55%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This reading was very confusing to me."

"Can you explain how string thickness affects speed? I am looking at the formula for a (standing wave) string fixed on both ends and I don't see the math."

"It's cool how these things relate to music."

"I now understand wave parameters better due to the examples we did in class. That was helpful."

"Haven't had as much time as I'd like to review last Wednesday's lecture, but wanted to mention that I am appreciative of the format of this course. Despite how fast-paced it is, I feel the previews of the blog and the repetition involved with the sample questions (initial exposure before the lecture, seeing them worked out during lecture, and trying them again in the post-lecture) is very helpful in cementing understanding. These are the sort of study techniques that are often advised, but I have usually dismissed them as overkill. Being required to follow through has been very conducive to my understanding of this material."

"I have nothing interesting to say :/" (Sometimes that's just the way it is.)

"Do you play an instrument? (In grade school, we learned how to play the most played instrument ever in history.)

20171119

Student lab reports: instructor comments

Physics 205A Lab 9, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students have a weekly laboratory, where are gradually introduced to best practices in collecting data, graphing and analysis, and writing a report with a descriptive abstract, procedure, and evidence-based conclusion. Over the course of a semester this is done via a backwards-scaffolding method, where the first reports including all of these sections are written individually and independently by students approximately two-thirds into the semester.

Selected instances of comments from the instructor are given below for each section.

1. Descriptive abstract
  • Written in present-, future-, or mixed-tense, instead of past-tense?
  • No mention that mathematical model was validated experimentally?
  • Passive voice used instead of active voice and first-person pronouns ("we" or "I")?
  • Inclusion of results, conclusions, and/or opinions?
  • Redundant/irrelevant statements?
2. Procedure
  • Unclear how someone who has not done this experiment would have a general idea what was done?
  • Diagram, but no labels?
3. Data table, calculations and/or results
  • Data table and/or graph not included with report?
  • No error bars on graph?
  • Error bars are default ±1 value, instead of based on actual "least count" column in data table?
  • Error bars are selected to be "standard error," when this is not statistically relevant to the data population for this experiment?
  • Results of validating trendline equation with experimental data incomplete or missing?
4. Evidence-based conclusion statement
  • Subjective claims not supported by data or specific numbers ("good," "faulty," "a better fit")?
  • Statements do not explicitly include specific numbers and data, such that they cannot be read/cited without having to refer back to the data table/graph?
  • Speculation ("we could have got better data if...," "most likely this error came from...")?

20171117

Physics quiz question: 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 :   ****** [mean = 23.7 +/- 9.0]
24.5-32.0 :   *********
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.

(Response (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!)