20150930

Physics quiz archive: vectors, projectile motion, forces

Physics 205A Quiz 3, fall semester 2015
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz03re3T



Sections 70854, 70855, 73320 results
0- 6 :   * [low = 6]
7-12 :   *
13-18 :   *******************
19-24 :   ****************************** [mean = 22.4 +/- 4.9]
25-30 :   ********************** [high = 30]

Online reading assignment: quantum leaps, sun's outer layers (SLO campus)

Astronomy 210, fall semester 2015
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 quantum leaps, and the sun's outer layers.


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.
"Electrons have the correct energies to be able to jump up to orbits in order jump down and give off photons."

"That sunspots come in pairs. I never knew that! It is interesting because this happens due to temporary magnetic regions that they have."

"Everything is interesting since I am not too familiar with this section."

"How Egyptians viewed/explained the sun as having wings and fire-spitting cobras. It was like a mini-history lesson within the astronomy material."

"How hot the sun is. Like, I knew it was hot, but wow."

"That sunspots aren't hotter than the rest of the sun's surface."

"I really enjoyed the presentation on quantum mechanics. Until I read about it in the book, I assumed that knowledge of quantum mechanics was outside of my scope of understanding. The movement of electrons from one orbit to the next was very cool."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Sunspots being temporary magnetic regions on the sun."

"Chemistry!"

"Photons and electrons to be particularly confusing. Mostly because I haven't taken chemistry in quite a few years."

"Chemistry is almost as dry of reading as history! But not too bad, just takes a little time."

"The analogy between a lightbulb filament and sunspots."

"Electrons and how they move orbits by photons. It's all a little wordy to understand, maybe we can dumb it down in class a little, with a flow chart or something :)"

"Nothing was too confusing to me."

An electron in an atom must emit a photon when it jumps from a __________ energy orbital to a __________ energy orbital.
lower; higher.  ****** [6]
higher; lower.  ******************************* [31]
(Both of the above choices.)  * [1]
(Unsure/guessing/lost/help!)  * [1]

An electron in an atom must absorb a photon when it jumps from a __________ energy orbital to a __________ energy orbital.
lower; higher.  ******************************* [31]
higher; lower.  ******* [7]
(Both of the above choices.)  [0]
(Unsure/guessing/lost/help!)  * [1]

The exterior of the sun, from inner to outermost layers, are the:
(Only correct responses shown.)
inner: photosphere [74%]
middle: chromosphere [79%]
outer: corona [72%]

State your preference regarding miso soup.
Strongly dislike.  [0]
Dislike.  [0]
Neutral.  ****** [11]
Like  ******* [7]
Strongly like.  ******************** [20]
(I don't know what miso soup is.)  * [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"If I have only done like 4 homeworks am I failing?" (Then you've only missed two so far, and if you don't miss any more, you'll still get a 100% on the online reading assignment points.)

"Is extra-credit available at some point?" (Yes. Sooner than you think.)

"I'm finding the group work very difficult for learning purposes. It's hard to never have my own paper personally graded because that's the way I learn what mistakes I need to fix. Next class I'll try printing out the handouts/in-class assignments and using them in class to see if that helps." (Yes, many students do just that.)

"I LOVE MISO SOUP THANK YOU FOR ASKING." (You're welcome.)

"Miso is the best when mixed with rice and Sriracha. Mmmm...home cookin'." (#dayum)

"The miso soup I usually get is stagnant, only when I stir the soup then I see movement." (Sounds like someone needs to order piping hot miso for homework.)

Online reading assignment: energy conservation

Physics 205A, fall semester 2015
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 energy conservation.


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.
"I did not understand most of it."

"The weight force of Earth on an object is a conservative force, as when this gravitational force does work against an object, removing its energy, it is able to store this energy, and return it to the object by later doing work on the object, therefore we talk about the increases or decreases in gravitational potential energy."

"The concept that energy cannot be created nor destroyed. It is only stored and transferred into different forms."

"Elastic potential energy: when a rubber band is stretched, there is a higher energy than when it is relaxed."

"There are conservative and nonconservative forces that can act on things. Elastic and gravitational potential energies are conservative. These can be used for mechanical or useful energy."

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 am trying to grasp all of these concepts I'm not really aware of what I need to work on."

"I found most of it confusing."

"How to tell if gravitational potential energy is increasing or decreasing."

"Just please lecture on the important points in this section. Nothing is too confusing a long as it is properly explained."

"I don't fully understand about gravity being a conservative force, and where or how it stores energy."

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.
decreases; increases.   ************************************ [36]
increases; decreases.   ***************** [17]
(Unsure/lost/guessing/help!)   ***** [5]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.
decreases; increases.   ****** [6]
increases; decreases.   ************************************************ [48]
(Unsure/lost/guessing/help!)   **** [4]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)
Translational kinetic energy: increases. [65%]
Gravitational potential energy: decreases. [64%]
Elastic potential energy (of the bungee cords): increases. [59%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:
her translational kinetic energy.   ********** [10]
her gravitational potential energy.   **************************** [28]
the elastic potential energy of the bungee cords.   ******** [8]
(Unsure/lost/guessing/help!)   ************ [12]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Please help. I think 'unsure/lost/guessing/help' is the #motto today."

"Gravitational potential energy and elastic potential energy are pretty straightforward."

"I would benefit from more examples of the energy conservation problems."

"Whew--a lot covered in these section, but will be ready to dive in and reinforce tomorrow."

"Uh...I dunno about these. I understand that if one type of energy increases, the others have to decrease to compensate (since energy cannot be created nor destroyed or something like that), but I will definitely need some explanation on these."

20150929

Online reading assignment: quantum leaps, sun's outer layers (NC campus)

Astronomy 210, fall semester 2015
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 quantum leaps, and the sun's outer layers.


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 glowing disk of the sun at sunset is 109 times the diameter of Earth's. It is absolutely amazing to me that there can be things so much bigger than Earth."

"Basically, reading about the sun was pretty interesting. I liked reading about sunspots--had no idea that even existed."

"I it interesting that you referred to miso soup as 'sun-surface soup.'"

"I thought it was mind-boggling to look at an image of the photosphere and the process of granulation and try to imagine that each granule represented was about the size of Texas."

"I've never known much about the sun and now I do and it makes me happy."

"I found it interesting how the ancient Egyptians represented the chromosphere with the sun having wings and cobras spitting fire. Looking at the slide from the presentation I can see how they would see that."

"I think it's crazy how exact electrons have to be when absorbing or releasing photons in order to move from one energy level to the next."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I've never been very good with chemistry so I still get a little confused whenever it comes to that."

"I got a little bit lost on the section discussing atoms. I think it was just a lot of terminology and I was failing to understand the process behind each term i.e. permitted orbits, quantum jumps, etc."

"I'm still a bit lost on sunspots and how they are compared to magnets and TVs."

"It's hard for me to contemplate the heat of the suns surface because of how hot it supposedly is."

"What I found confusing is how sunspots on the sun's surface are cool, when the sun is so hot. I don't understand how it's caused by the strong magnetic fields."

An electron in an atom must emit a photon when it jumps from a __________ energy orbital to a __________ energy orbital.
lower; higher.  ****** [6]
higher; lower.  ********* [9]
(Both of the above choices.)  *** [3]
(Unsure/guessing/lost/help!)  [0]

An electron in an atom must absorb a photon when it jumps from a __________ energy orbital to a __________ energy orbital.
lower; higher.  ************ [12]
higher; lower.  ***** [5]
(Both of the above choices.)  * [1]
(Unsure/guessing/lost/help!)  [0]

The exterior of the sun, from inner to outermost layers, are the:
(Only correct responses shown.)
inner: photosphere [67%]
middle: chromosphere [72%]
outer: corona [67%]

State your preference regarding miso soup.
Strongly dislike.  [0]
Dislike.  ** [2]
Neutral.  ** [2]
Like  **** [4]
Strongly like.  ******* [7]
(I don't know what miso soup is.)  *** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Did you see the lunar eclipse?" (No, it was cloudy. #fml)

"Many things that we have discussed in class about the other planets around us is from assumptions. What if most of it is wrong?" (Then science is progressing. #themoreyouknow)

"What is miso soup?" (For those of you who don't even know what that is, go and try miso soup for homework.)

"Why the question about miso soup?" (Because, it's delicious. Also, physics.)

"I can read the textbook but I find that when you give a brief overview I suddenly get that 'ah ha' moment." (I live for moments like that.)

20150928

Online reading assignment: work and energy

Physics 205A, fall semester 2015
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 work and energy.


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.
"Even if a force is acting on an object, the work done on that object will be zero if it is not moved. Work is computed using the part of the force acting in the direction of movement."

"Work acting on an object increases its translational kinetic energy and that work acting against it reduces the translational kinetic energy."

"Translational kinetic energy is measured in joules. Work results in the change of translational kinetic energy."

"Work is accomplished by exerting a force over a displacement. Work can be done on or against any mechanical energy form or forms."

"How changes in kinetic energy relates to work, and how forces can do work on an object rather than just result in a net force."

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 honestly feel very good about these concepts, and don't currently don't feel confused on the reading."

"I get this sections and its concepts. What I don't understand is where, and how the work-energy theormen was derived."

"The concept of 'work.' I don't understand the concept of it and how to quantitatively describe 'work.'"

Explain how the SI (Système International) unit for work is related to the SI unit for force.
"The units are related by a ratio of one-to-one."

"They are both joules."

"The unit of work is the unit of force times the unit of distance."

"A newton·meter = joule."

Match the description of the work exerted by these forces for each object. (Only correct responses shown.)
Pushing in the same direction of motion: work done "on" the object (positive work). [88%]
Pushing opposite the direction of motion: work done "against" the object (negative work). [93%]
Pushing 90° sideways to the direction of motion: no work done. [57%]
Pulling such that the angle between the force and motion is an acute angle (between 0° and 90°): work done "on" the object (positive work). [58%]
Pulling such that the angle between the force and motion is an obtuse angle (between 90° and 180°): work done "against" the object (negative work). [52%]

For the catapulted squirrel, the bungee cord force does work __________ the squirrel, which __________ the squirrel's translational kinetic energy.
on; increases.   ********************************************************* [57]
against; decreases.   ********** [10]
(Unsure/lost/guessing/help!)   [0]


For the braking car, the brakes do work __________ the car, which __________ the car's translational kinetic energy.
on; increases.   ***** [5]
against; decreases.   ************************************************************** [62]
(Unsure/lost/guessing/help!)   [0]


For Mrs. P-dog being catapulted, the bungee cords do work __________ Mrs. P-dog, while the weight force does work __________ Mrs. P-dog.
on; on. *** [3]
on; against.   **************************************************** [52]
against; on.   ***** [5]
against; against.   *** [3]
(Unsure/lost/guessing/help!)   **** [4]


For Mrs. P-dog's translational kinetic energy to be increased while being catapulted, the amount of work from the bungee cords must be __________ the amount of work from the weight force.
less than.   * [1]
the same as.   *** [3]
greater than.   ************************************************************** [62]
(Not enough information is given.)   [0]
(Unsure/lost/guessing/help!)   * [1]


Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Was that your squirrel catapult?" (I wish it was. #squadgoals)

"Hmm....I didn't know I had to answer this portion of the reading assignment to get full credit!" (Eh, not really. Unless you left every other free-response part of the reading assignment blank.)

"How do I determine whether the work done on an object is positive or negative just by knowing the angle between the force and displacements on that object?" (We'll cover this briefly at the start of tomorrow's class.)

"This stuff only gets harder." (Really? After the first midterm each of these chapters is more self-contained, and thus does not critically depend on previous chapters. #ymmv)

20150926

Astronomy current events question: Saturn's warmer than expected "A" ring

Astronomy 210L, fall semester 2015
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!)
Preston Dyches, "At Saturn, One of These Rings Is Not Like the Others" (September 2, 2015)
jpl.nasa.gov/news/news.php?feature=4709
Comparison of computer__________ models with data taken by NASA's Cassini spacecraft may explain the warmer than expected temperatures of Saturn's "A" ring.
(A) convection current.
(B) particle composition.
(C) magnetic field.
(D) gravitational.
(E) greenhouse effect.

Correct answer: (B)

Student responses
Sections 70178, 70186
(A) : 2 students
(B) : 20 students
(C) : 3 students
(D) : 2 student
(E) : 3 students

Astronomy current events question: variations in Mercury's rotational speed

Astronomy 210L, fall semester 2015
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!)
Leigh Cooper, "Mercury’s Movements Give Scientists Peek inside the Planet" (September 9, 2015)
blogs.agu.org/geospace/2015/09/09/mercurys-movements-give-scientists-peek-inside-the-planet/
Mercury's core composition and gravitational interactions with the outer planets can be analyzed from __________ data measured by NASA's Messenger spacecraft.
(A) seismic.
(B) rotation rate.
(C) temperature.
(D) polar ice.
(E) magnetic field.

Correct answer: (B)

Student responses
Sections 70178, 70186
(A) : 1 student
(B) : 20 students
(C) : 3 students
(D) : 1 student
(E) : 5 students

Astronomy current events question: comet 67P Churyumov-Gerasimenko's "neck"

Astronomy 210L, fall semester 2015
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!)
Emily Lakdawalla, "How the Duck Got Its Neck: Rapid Temperature Changes from Self-Shadowing May Explain 67P's Unusual Activity and Shape" (September 11, 2015)
planetary.org/blogs/emily-lakdawalla/2015/09110855-how-the-duck-got-its-neck.html
Computer modeling of __________ may explain how comet Churyumov-Gerasimenko's "neck" developed over time.
(A) rapid temperature changes.
(B) random collisions.
(C) rotation rates.
(D) gravitational fields.
(E) seismic instability.

Correct answer: (A)

Student responses
Sections 70178, 70186
(A) : 22 students
(B) : 2 students
(C) : 1 student
(D) : 3 students
(E) : 2 students

20150925

Presentation: energy conservation

Bike, meet hill. Hill, meet bike lift. Bike lift. (Video link: "Bicycle Lift ‘Steep is nothing’ -Panasonic ecoideasnet.")

In this presentation we will complete our introduction to the most common mechanical forms of energy that can be readily transferred amongst each other, along with how this mechanical energy can be irreversibly lost, or irreversibly replenished in the framework of energy conservation.

First, a discussion on forces such as the gravitational weight force, and the force of elastic materials and springs, and how the work done by these forces can be stored and later retrieved without loss. Thus these forces are said to be "conservative," as opposed to non-conservative forces that do work that irreversibly loses or gains energy.

The weight force of Earth on an object is a conservative force, as when this gravitational force does work against an object, removing its energy, it is able to store this energy, and return it to the object by later doing work on the object. Because of this, instead of explicitly calculating the work done against or an object by the weight force during these storage/retrieval processes, it is much more convenient to talk about increases or decreases in this gravitational "potential" energy.

Gravitational potential energy depends on the mass m of the object, the gravitational constant g, and the elevation y of that object. The resulting units of kg·m2/s2 are equivalent to joules. An object on the ground has zero gravitational potential energy, and the higher elevation it has, the more gravitational potential energy it has.

Instead of finding out how much gravitational potential energy PEgrav an object has, often we are more concerned with its initial-to-final change ∆PEgrav, which is the final amount of gravitational potential energy minus the initial amount of gravitational potential energy. Notice how the common factors of m and g (which are presumed to be constant) are pulled out, leaving a "difference of elevations" for the final and initial values of y in the parenthesis.

The elastic force of "stretchy" material such as rubber tubing (as in this slingshot), or springs is another conservative force, as when this elastic force does work against an object, removing its energy, it is able to store this energy, and return it to the object by later doing work on the object. Because of this, instead of explicitly calculating the work done against or an object by an elastic force during these storage/retrieval processes, it is much more convenient to talk about increases or decreases in this elastic "potential" energy.

Elastic potential energy depends on the elastic/spring constant k (which is a measure of how difficult it is to stretch/compress) and the distance x that the elastic/spring is stretched/compressed from its relaxed equilibrium (where x is set to be zero). The resulting units of N·m are equivalent to joules. A relaxed elastic/spring contains zero elastic potential energy, and the further it is stretched or compressed from its relaxed state, the more elastic potential energy it has.

Instead of finding out how much elastic potential energy PEelas an object has, often we are more concerned with its initial-to-final change ∆PEelas, which is the final amount of elastic potential energy minus the initial amount of elastic potential energy. Notice how the common factors of (1/2) and elastic/spring constant k (which is presumed to be constant) are pulled out, leaving a "difference of squares" for the final and initial values of x in the parenthesis.

Keep in mind that gravitational potential energy and elastic potential energy involve the conservative forces of weight and of elastic materials, which ideally work against or on objects to receive, store, and return energy without loss. Combined with translational kinetic energy KEtr, PEgrav and PEelas are the useful "mechanical" forms of energy that can be readily transferred between each form for current or later use.

In contrast, when non-conservative forces are exerted against the motion of objects, energy is lost, irreversibly converted to non-mechanical forms; or when non-conservative forces work along the motion of objects, energy is gained, but this is from the irreversible conversion of non-mechanical forms.

Here we have many examples of non-conservative forces acting on the cat. As it slides across the floor, friction and drag act against the direction of motion of the cat, removing its translational kinetic energy, and it eventually slows to a stop. This energy is irreversibly lost, dissipated to heating up the cat, contact surfaces, and stirring up the air in the room, and cannot be recovered.

Also the people at either end of the kitchen push on the cat along its direction of motion, adding to its translational kinetic energy. This energy is irreversibly converted from the biochemical reactions in the people, and cannot be recovered.

Because these non-conservative forces involve irreversible transfers to/from mechanical energy forms, we must explicitly account for the non-conservative work done by them in energy conservation accounting.

Second, accounting for the transfers between different mechanical energy forms, and also for the contribution to or taking from these energies by non-conservative work.

In contrast to the "incomplete" work-energy theorem, this is the complete form of total energy conservation equation, which shows how the transfer of energy (as work is done by non-conservative forces acting on or against the motion of the object) causes a corresponding change in the translational kinetic energy of the object, along with the potential gravitational energy and the potential elastic energy. Any or all of these energy forms on the right-hand side of the equation can increase or decrease, but together all of their changes must add up to the corresponding non-conservative work term on the left-hand side of this equation.

Note that in the idealized case that there are no non-conservative forces (such as friction, drag, or from external sources), then the left-hand size of this equation would be zero. Then the individual energy terms on the right-hand side of this equation can then trade and balance amongst themselves, instead of with the outside world.

So now let's see how this transfer/balance equation can be applied to idealized situations where friction and drag are negligible.

Just after being launched by this "water catapult," while the woman moves upwards, does her translational kinetic energy increase or decrease? Does her gravitational potential energy increase or decrease?

Assuming that there is no friction/drag (such that we can neglect non-conservative work), is energy being transferred from translational kinetic energy to gravitational potential energy, or is it transferred the other way around? (Video link: "Human Water Catapult - 55 Foot Launch! In 4k (HD).")

Just after being released from rest, while the ball bearing is being launched by this slingshot, does its translational kinetic energy increase or decrease? Does the elastic potential energy of the slingshot bands increase or decrease?

Assuming that there is no friction/drag (such that we can neglect non-conservative work), is energy being transferred from translational kinetic energy to elastic potential energy, or is it transferred the other way around? (Video link: "The Physics of Slingshots 2 | Smarter Every Day 57.")

For the woman bungee jumper, starting from when she just begins to slide to when the bungee cord is fully stretched as she sways back-and-forth at her lowest point of descent, does her translational kinetic energy increase or decrease? Does her gravitational potential energy increase or decrease? Does the elastic potential energy of the bungee cord increase or decrease?

Assuming that there is no friction/drag (such that we can neglect non-conservative work), which energy system experienced a greater amount of change: the gravitational potential energy or the elastic potential energy? (Video link: "Homemade Bungee jump.")

20150924

Presentation: work and energy

Tarp-lined ramp leading down to a pond? Check. All-terrain vehicle? Check. Pulling a cord attached to a raft and rider? Whee! (Video link: "Human Slingshot Slip and Slide - Vooray.")

In this presentation we will introduce a new connection between forces and motion, in terms of how forces can do work on or against an object in order to speed up or slow down its motion. This is a new approach to connecting forces and motion, compared to the previous discussion in this course of using Newton's laws to relate how forces on an object result in a net force that may or many not change its motion.

First, defining the "amount of motion" of an object in terms of its translational kinetic energy, and then expressing how a force may do work on or against the motion of an object.

Translational kinetic energy KEtr is the energy of motion. (We'll deal with rotational kinetic energy KErot later on.)

Translational kinetic energy KEtr depends on the mass m and the square of the speed v of the object, and the resulting units of kg·m2/s2 are also expressed as joules. A stationary object has no translational kinetic energy, and the faster an object moves, the more translational kinetic energy it has.

Instead of finding out how much translational kinetic energy KEtr an object has, often we are more concerned with its initial-to-final change ∆KEtr, which is the final amount of translational kinetic energy minus the initial amount of translational kinetic energy. Notice how the common factors of (1/2) and mass m (which is presumed to be constant) are pulled out, leaving a "difference of squares" for the final and initial speeds in the parenthesis.

In order to change the translational kinetic energy of an object (speeding it up or slowing it down), a force (such as that exerted by the horses) must do a certain amount of work W either on, or against the motion of the object (here the loaded sledge the horses are pulling).

Work is accomplished by exerting a force on an object, but in such a way that the object moves through a displacement s (note the unusual use of "s" for a generic ∆x, ∆y, or other direction displacement!), and the angle between the force and displacement vectors (when placed tail-to-tail) is anything besides 90°. The units of work are given in N·m, or yet again, joules, so keep in mind that work can be done on or against any mechanical energy form or forms.

Second, let's now explicitly make the connection between the work done by a force acting on or against the motion of an object, and the resulting changes in translational kinetic energy of the object.

This is an incomplete form of the total energy conservation equation we will utilize later, but this "work-energy theorem" shows how the transfer of energy (as work is done by a force acting on or against the motion of the object) causes a corresponding change in the translational kinetic energy of the object.

If the force does work on the object (by being exerted along the direction of its motion), then the work will have a positive sign, and the translational kinetic energy of the object will increase, making the sign of the ∆KEtr term positive. Note for this case how the left- and right-hand sides of this equation must have the same positive sign.

If the force does work against the object (by being exerted opposite to the direction of its motion), then the work will have a negative sign, and the translational kinetic energy of the object will decrease, making the sign of the ∆KEtr term negative. Note for this case how the left- and right-hand sides of this equation must have the same negative sign.

Squirrel. Catapult! Squirrel catapult! (Video link: "squirrelcatapult.gif.")
For the catapulted squirrel, the bungee cord force does work __________ the squirrel, which __________ the squirrel's translational kinetic energy.
(A) on; increases.
(B) against; decreases.
(C) (Unsure/lost/guessing/help!)

Note as this car stops, the brakes glow from the heat generated! As this happens, does the force of the brakes do work on, or against the motion of the car? Does the translational kinetic energy of the car increase or decrease for this process? (Video link: "McLaren SLR review - Top Gear - BBC.")
For the braking car, the brakes do work __________ the car, which __________ the car's translational kinetic energy.
(A) on; increases.
(B) against; decreases.
(C) (Unsure/lost/guessing/help!)

Don't blink, or you'll miss Mrs. P-dog in action! (Video link: "110530-1230869-excerpt.")
For Mrs. P-dog being catapulted, the bungee cords do work __________ Mrs. P-dog, while the weight force does work __________ Mrs. P-dog.
(A) on; increases.
(B) against; decreases.
(C) (Unsure/lost/guessing/help!)

For Mrs. P-dog's translational kinetic energy to be increased while being catapulted, the amount of work from the bungee cords must be __________ the amount of work from the weight force.
(A) less than.
(B) the same as.
(C) greater than.
(D) (Not enough information is given.)
(E) (Unsure/lost/guessing/help!)

20150923

Online reading assignment: runaway planets, jovian planets, and dwarf planets (oh my!) (SLO campus)

Astronomy 210, fall semester 2015
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 runaway planets (Venus and Mars), jovian planets (Jupiter, Saturn, Uranus and Neptune), and the dwarf planets (and the International Astronomy Union classification scheme).


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.
"Venus and Mars can be considered the 'runaway' planets."

"That Pluto isnt a planet anymore. Ive known that for a while but I never knew why it wasn't considered a planet anymore."

"The history of the planets, as I got a better idea of how they compare to Earth."

"Even though Uranus and Neptune have about the same mass, and Neptune is further from the sun, yet Uranus has a colder atmosphere."

"How core heat and sunlight make weather more active and colorful on Jupiter compared to Saturn. "

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Why was Pluto considered a planet before? It seems weird that they just changed the rules and kicked Pluto out."

"Would really like a better explanation as to why uranus and neptune are so similar and yet look so different."

"The gravy analogy. How the formation of volcanoes can pause and 'sleep.' I'm not sure exactly how this works and if the volcano is in a cooling state or in a resting state."

"Nothing confusing. I'm really looking forward to moving out of our solar system, but I understand that we need to know the basics first."

"How gas particles escaped from Mars thus dissipating its atmosphere."

Identify the relative amounts of these characteristics for Venus, compared to Earth. (Only correct responses shown.)
Interior core heat, today: about the same as Earth [50%]
Geologic activity, today: less than Earth [91%]
Volcanic outgassing, up until now: about the same as Earth [76%]
Heat from the sun: more than Earth [32%]
Amount of atmosphere, today: more than Earth [65%]

Identify the relative amounts of these characteristics for Mars, compared to Earth. (Only correct responses shown.)
Interior core heat, today: less than Earth [82%]
Geologic activity, today: less than Earth [85%]
Volcanic outgassing, up until now: less than Earth [71%]
Heat from the sun: less than Earth [71%]
Amount of atmosphere, today: less than Earth [71%]

Which jovian planet has the coolest interior temperatures?
Jupiter (most massive).   ** [2]
Saturn (most prominent rings).   *** [3]
Uranus (least active weather patterns).   ***************** [17]
Neptune (farthest from the sun).   ************ [12]
(Unsure/guessing/lost/help!)   [0]

I believe Pluto should be a planet.
Strongly disagree.   * [1]
Disagree.   ******** [8]
Neutral.   *************** [15]
Agree.   ******* [7]
Strongly Agree.   *** [3]

Briefly explain your answer to the previous question (whether Pluto should be a planet).
"I think that it should be considered a planet because it orbits the sun. Just because it doesn't fit into the terrestrial or jovian category doesn't mean it should be disregarded. "Pluto doesn't posses characteristics similar of those to jovian or terrestrial planets. As explained in the book it is more of a icy cold little object and there are tons it therefore I don't consider it a planet."

"I believe that Pluto is a planet because it orbits the sun and that qualifies it as a planet."

"It has certain aspects that could and couldn't make it a planet so I decided to stay neutral."

"It already was considered a planet. It still revolves around the sun no matter what we call it."

"Until more recently, I grew up learning about Pluto as a planet so do not really understand the sudden change."

It was a planet for 76 years, so I think it should have stayed that way."

"Pluto does not dominate its orbit, which makes it a dwarf planet."

"Pluto is much more similar to the family of icy worlds found recently than it is to the other eight planets in the solar system."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I wasn't able to make it last class to the quiz. You drop three quizzes, correct?" (Yes.)

"Could we possibly go over last week's quiz?" (You need to do that yourself, but feel free to ask me questions when I'm circulating through the class during group work, just after class, in office hours, or make an appointment, or e-mail me. In any case, we'll have a practice quiz tonight to review the earlier quizzes, as well as the new material covered on the quiz next week.)

"Can we go over the geologic activity of Venus and Mars in relation to Earth?" (Yes, looking over some of your responses on this online reading assignment, we'll need to.)

Online reading assignment: uniform circular motion

Physics 205A, fall semester 2015
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 uniform circular 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.
"A centrifugal force appears to push outwards on us when in fact the net force acts inwards, to keep it moving in a circular motion."

"The requirement for uniform circular motion is that the net force must be exactly equal to mv2/r, and be directed in towards the center."

"Uniform circular motion is related to Newton's second law."

"An object in uniform circular motion is constantly accelerating towards the center of the circle. A 'centripetal' force is not actually a force; it just describes the net force acting towards the center of a circle in uniform circular motion."

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.
"Everything. I have no idea how to apply any of these concepts and barely understand the basics of them."

"I have a preliminary understanding of circular motion, at face value, but I think it would be very helpful to go over examples in class."

"I think I understand this part pretty well."

For the "drifting" car (skidding around a circular track at constant speed), Newton's __________ law applies to its motion, and the forces acting on it add up to a net force that:
first; is zero.   ******** [8]
second; points to the left.   *********************** [23]
second; points to the right.     *********************** [23]
(Unsure/lost/guessing/help!)   **** [4]


At the moment when the woman is at the bottom of her swinging trajectory (when the rope is vertical), Newton's __________ law applies to her motion, and the forces acting on her add up to a net force that:
first; is zero.   **************** [16]
second; points upwards.     *************************** [27]
second; points downwards.   ********** [10]
(Unsure/lost/guessing/help!)   ***** [5]


At the moment when the motor scooter is on the left side of the screen (traveling out at you), Newton's __________ law applies to its motion, and the forces acting on it add up to a net force that:
first; is zero.   ********* [9]
second; points to the left.   ***************** [17]
second; points to the right.   ************************ [24]
(Unsure/lost/guessing/help!)   ******** [8]


At the moment when the car is at the very top of the loop-the-loop, Newton's __________ law applies to its motion, and the forces acting on it add up to a net force that:
first; is zero.   ***************************** [29]
second; points upwards.   ********* [9]
second; points downwards.     ************************* [25]
(Unsure/lost/guessing/help!)   **** [4]


At the moment when a person is at the right edge of the screen (traveling out at you), Newton's __________ law applies to his/her motion, and the forces acting on him/her add up to a net force that:
first; is zero.   *** [3]
second; points to the left.   ************************** [26]
second; points to the right.   ***************** [17]
(Unsure/lost/guessing/help!)   ************ [12]


At the moment when the car is at the very top of its mid-air trajectory, Newton's __________ law applies to its motion, and the forces acting on it add up to a net force that:
first; is zero.   ************* [13]
second; points upwards.   ********** [10]
second; points downwards.   *************************** [27]
(Unsure/lost/guessing/help!)   ******** [8]


At the moment when the skateboarder is at the very top of his mid-air trajectory, Newton's __________ law applies to his motion, and the forces acting on him add up to a net force that:
first; is zero.   ***************** [17]
second; points upwards.   ***** [5]
second; points downwards.   ****************************** [30]
(Unsure/lost/guessing/help!)   ****** [6]


Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I'm confused as to how circular motion applies to everyday life. I'm not fully understanding how the pictures show the centrifugal forces." (A "centrifugal" force is not one of the actual mechanical forces (w, N, T, fs, or fk). #smh)

"I'm not sure which way the net forces are acting in the examples above, so I was taking educated guesses." (#facepalm)

"Are the the net forces always towards the center of the circle (downward if at the top, upward if at the bottom, right if it's going left, left if it's going right)?" (Yes--yes, yes, yes, and yes.)

"Do we get marked down for checking 'unsure/lost/guessing/help!' or 'honestly didn't get to it yet' in our online homework?" (You will still receive full credit. Unless you leave the comment boxes blank, so put something substantive in there--even if you got nothing, at least tell me what's going on in your life that is interfering with studying physics this week.)

"7-Up or Sierra Mist?" (Meh. I do miss dnL, which was the "uʍop ǝpᴉsdn" edition of 7-Up.)

20150922

Online reading assignment: runaway planets, jovian planets, and dwarf planets (oh my!) (NC campus)

Astronomy 210, fall semester 2015
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 runaway planets (Venus and Mars), jovian planets (Jupiter, Saturn, Uranus and Neptune), and the dwarf planets (and the International Astronomy Union classification scheme).


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.
"Venus may have been similar to Earth, just with a different atmosphere, and being slightly closer to the sun."

"All of the histories of the planets. What astronomers think the planets were like billions of years ago. And to think that some planets might have had life forms, billions of years ago."

"That Hawaii has shield volcanoes like the ones on Mars."

"How sunlight affects the color of the clouds in the atmosphere of Jupiter and Saturn."

"Learning about planets' atmospheres because it helps me understand why we can have life on Earth and not on other terrestrial planets."

"That Venus and Mars were both considered runaway planets."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Why Pluto was deemed not a planet in 2006. I get the reasoning, but it just seems stupid."

"Atmosphere stuff: outgassing, retention, carbon cycles. All of it."

"There is no plate tectonics on Venus, how is that true?"

Identify the relative amounts of these characteristics for Venus, compared to Earth. (Only correct responses shown.)
Interior core heat, today: about the same as Earth [33%]
Geologic activity, today: less than Earth [59%]
Volcanic outgassing, up until now: about the same as Earth [41%]
Heat from the sun: more than Earth [81%]
Amount of atmosphere, today: more than Earth [63%]

Identify the relative amounts of these characteristics for Mars, compared to Earth. (Only correct responses shown.)
Interior core heat, today: less than Earth [85%]
Geologic activity, today: less than Earth [56%]
Volcanic outgassing, up until now: less than Earth [70%]
Heat from the sun: less than Earth [74%]
Amount of atmosphere, today: less than Earth [70%]

Which jovian planet has the coolest interior temperatures?
Jupiter (most massive).   ** [2]
Saturn (most prominent rings).   ** [2]
Uranus (least active weather patterns).   ****** [6]
Neptune (farthest from the sun).   *********** [11]
(Unsure/guessing/lost/help!)   ****** [6]

I believe Pluto should be a planet.
Strongly disagree.   ** [2]
Disagree.   ** [2]
Neutral.   ************* [13]
Agree.   ******* [7]
Strongly Agree.   *** [3]

Briefly explain your answer to the previous question (whether Pluto should be a planet).
"Based on the current definition Pluto is not a planet. However, just because we want to change the definition does not mean that Pluto should suffer."

"Since Pluto has moons, then to me it is a planet."

"I don't know enough about Pluto to make a clear decision."

"Pluto is cute and I think it is sad to declare it a planet then take it away."

"Live and let live. I have always known Pluto as a planet."

"I don't really care much. I kind of feel like, why change it now? But now that I've read a bit more, Pluto doesn't meet some of the criteria to be considered a planet so I understand them making the change."

"I grew up with Pluto being labeled a planet. But now it's not and I'm not bothered by it."

" If we let Pluto be a planet, we'll probably have to let other dwarf planets (Eris, Ceres, etc.) be planets as well."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I need more lecture time in class." (Well, sure, as long as you keep telling me specifically what you need more clarification on.)

"I would like it if we had more time to review for the quizzes. I studied a good amount of time and still did bad on the last quiz. Maybe I am studying the wrong things, or just not understanding. It would be helpful if we went over it more in class." (Let's have a discussion later about what you're doing (or not doing). Meanwhile, we'll have a practice quiz for review this week to prepare for the next upcoming quiz.)

"What are your thoughts on Pluto? Do you believe it should be considered a planet?" (Did we not already talk about this on the first day of semester?)

20150921

Online reading assignment: applications of Newton's laws (friction)

Physics 205A, fall semester 2015
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 on applications of Newton's laws (emphasizing static and kinetic friction).


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.
"Static friction acts to prevent objects from starting to slide. Kinetic friction acts to try to make sliding objects stop sliding."

"Kinetic friction occurs when two objects are moving relative to each other while static friction is when the two objects are not moving. Kinetic friction is usually less than the static friction."

"Different materials have different coefficients of friction."

"Frictional forces are parallel to surfaces."

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.
"Still having difficulty distinguishing the differences of Newton's first law and the third law."

"The differences between static friction and kinetic friction. Not sure how they are different."

"I don't really understand how to identify the magnitudes of static and kinetic frictional forces, and how to tell the difference(s) between them."

"I got this."

"I would like to go over more problems and more thorough explanation of the concepts during lecture."

What is the meaning of the "normal" in the "normal force?"
"Perpendicular."

"The perpendicular component of the force that acts on the object from a surface."

"'Normal' force is the average force exerted."

"It's the force 'normally' existing because of gravity?"

"The force that is applied due to gravity."

"I'm not sure."

The SI (Système International) units of the static friction coefficient µs and the kinetic friction coefficient µk are:
"These are measured in newtons (N)."

"Micros."

"These coefficients are unitless."

Identify the magnitude of the static friction force fs for each of the following situations of a box that is initially stationary on a horizontal floor. (Only correct responses shown.)
No horizontal forces applied to it, so it remains stuck to the floor:
fs = 0. [78%]

A horizontal force applied to it, but still remains stuck to the floor:
fs = some value between 0 and µs·N. [75%]

A horizontal force applied to it, at the threshold of nearly becoming unstuck:
fs = µs·N. [73%]

Identify the magnitude of the kinetic friction force fk for each of the following situations of a box that is already sliding across a horizontal floor. (Only correct responses shown.)
No horizontal forces on it, so it slows down:
fk = µk·N. [20%]

A horizontal force applied in the forward direction, but not enough to keep the box going so it still gradually slows down:
fk = µk·N. [14%]

A horizontal force applied in the forward direction, just enough to keep the box going at a constant speed:
fk = µk·N. [58%]

A horizontal force applied in the forward direction, enough to gradually increase the speed of the box:
fk = µk·N. [47%]

A horizontal force applied in the backwards direction, such that the box slows down:
fk = µk·N. [29%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I don't understand static friction vs. kinetic friction--the book doesn't do a great job at explaining each and whether their magnitude is zero, or not zero, etc."

"I like your online presentation previews much more than only reading from the text."

"We're going to need to talk about this." (Yes. A lot.)

"Like that you lectured last time--I actually learned a little. Can you please keep doing it that way? But instead teach us everything that will be in the midterms :D" (Hopefully maybe such that you can answer essay questions on friction on the midterm. #dreams #squadgoals)

"I LOVE PHYSICS." (Yes, but does physics love you back? #noitdont)

20150919

Physics quiz question: speed(?) of pushed box

Physics 205A Quiz 3, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 4.85

A 5.0 kg box on a table is initially stationary, and then pushed with an applied force that is slowly increased from zero to 8.0 N. The coefficient of static friction between the box and table is 0.18. The coefficient of kinetic friction between the box and table is 0.15. After the applied force has reached and is maintained at a constant magnitude of 8.0 N, the speed of the box is:
(A) zero (stationary).
(B) slowing down.
(C) a constant non-zero value.
(D) speeding up.
(E) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The box has two vertical forces acting on it:
Weight force of Earth on box (downwards, magnitude w = m·g = 49 N).
Normal force of floor on box (upwards, magnitude N = 49 N).
Because the box is stationary in the vertical direction, these two forces are equal in magnitude and opposite in direction, due to Newton's first law.

The box has two horizontal forces acting on it:
Friction (static or kinetic) force of floor on box (to the left).
External applied force on box (to the right).
The (constant) magnitude of the kinetic friction force is fk = μk·N = (0.15)(49 N) = 7.4 N. The magnitude of the static friction force can vary anywhere from 0 to a maximum value of fs,max = μs·N = (0.18)(49 N) = 8.8 N. Because the applied force (increased from 0 to a maximum of 8.0 N) is less than the maximum static friction force magnitude of fs,max = 8.8 N, the actual magnitude of the static friction force would also be fs = 8.0 N to oppose the applied force, and the box would still remain stuck to the table.

Sections 70854, 70855
Exam code: quiz03sQr7
(No results available)