## 20121104

### Online reading assignment: ideal fluid flow, elasticity

Physics 205A, fall semester 2012
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 ideal flow, and elasticity.

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.
"Streamlines may curve and bend but not they cannot cross each other."

"Deformation. I like this because I am studying to be an architect. In projects you learn about this."

"Streamlined fluids--it's weird to think water and air can be used with the same equations."

"When a liquid is flowing, the higher the velocity the lower the pressure is. This seems seems counter intuitive and confusing but makes sense when relating it to the book examples of arterial flutter and airplane flight."

"Constant volume flow rate--as the area of a pipe decreases, the flow rate of the liquid will increase to keep the volume flow rate the same."

"A moving fluid can exert a force parallel to any surface over or past which it flows, and that viscosity it the fluids resistance to flow."

"I do not know how to answer this question, should I relate it to something that has happened to me?" (Or discuss why it makes you go, 'huh?' Or why it fascinates you, etc.)
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Bernoulli's equation--I don't understand the units for the different terms of the equation. How can each term have the same SI unit?"

"'Steady flow is laminar.' I still don't quite get how this works. How can there be no disruption between layers? How can you create these layers?"

"Nothing too confusing but I also found stress on a wire interesting because we use a ton of wire on the family farm for pulling things, making fences to keep the cows in, etc. It is cool to learn that stuff so we can determine the correct cable, wire, whatever it is to get a job done correctly and efficiently."

"Having a hard time telling the difference between incompressible/compressible and laminar/turbulent and why water can be all of these things."

"An ideal fluid is incompressible which was confusing because how or when can a fluid be compressed?" (Under many circumstances air can be compressed, making it not an ideal fluid.)

Also what if we don't have an ideal fluid? Do we just not do anything with it? (Yes, as in-depth analysis of non-ideal fluid flow requires concepts and models beyond the scope of this course.)
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"What does SI unit even mean?" (Système international d'unités, which is basically the 'metric system.')

"Seems very difficult to accurately determine the mass of the fluid passing a certain point at one time and comparing that mass to another mass of the fluid through a second section. How is that measured?" (If you are measuring the mass (or volume) of liquid flowing out the end of a section of pipe--just measure how long it takes for the stream of liquid to fill a bucket.)

"I like that we are learning a different chapter each week, but I feel like I will never be able to remember so much information for the midterm!"

"I didn't get this homework at all. Maybe I should try again tomorrow to see if I dream something that will help." (Sweet dreams!)

"Physics is fun. Especially when I get it." (Got it.)