Week 2

Fluids and Fluid Dynamics

Fluids and Fluid Dynamics (Ch. 14)

This week we're going over chapter 14 of Knight. We will focus on liquids: hydrostatics and hydrodynamics. The introductory sections compare gases and liquids while the last section talks about some of the fluid-like properties of solids.

Lectures

Additional lectures (from Spring 2020) are linked at the bottom of the page.

Tuesday: pdf of notes
Tue: intro
Tue: hydrostatics pt. 1
Tue: hydrostatics pt. 2
Thursday: pdf of notes
Thu: follow up from survey
Thu: fluid dynamics
Fri: Addendum: hydraulic press
- pdf notes
Fri: Addendum: fluid dynamic example
- pdf notes

Example Videos

From TA Ian Chaffey.

Ch. 14: Problem 19
Ch. 14: Problem 29

Learning Objectives This Week

Hydrostatics:
- How do hydraulic lifts work?
- What is the balance of forces for a floating object? (Buoyancy)
Fluid dynamics for an ideal fluid:
- Use conservation of mass (continuity) and conservation of energy (Bernoulli's equation) to relate the fluid velocity
Minor learning goals (won't show up in explainer, but useful for later):
- What do the Young's modulus and bulk modulus tell us about a solid?

Main Ideas

Fluids (liquids or gases) are macroscopic description of microscopic molecular motion. This will be a common theme in thermodynamics.
Pressure is force per area. It acts in all directions with equal magnitude.
Buoyancy is the force of "holding up" a small volume of fluid from falling.
- If you replace that small volume with something less dense, then the buoyant force pushes it upward against its weight.
Fluid dynamics (for ideal fluids in motion)
- Continuity equation: the rate of stuff entering a volume must match the rate of stuff exiting a volume
- Bernoulli's equation: conservation of energy for ideal fluids
There are quantities is analogous to pressure for solids.

Homework

Quick Survey

Due Wednesday.

Submission link: Quick Survey 2

Mastering Physics

Due Friday, graded for completion not for correctness. Unlimited retries. Use this to test out your understanding in a penalty-free environment. Please access Mastering Physics through the Pearson portal.

Explainer Videos

Due next Monday. This week you will have two videos; the assignments are below. The submission form has room to post two links.

Submission link: Week 2 Explainer Videos

Peer Review

Due next Monday. You are assigned three of your classmates' videos to watch and review.

Spreadsheet of peer review assignments.
Rubric for how to grade
Submission link: Peer Review of Explainer #1; use the same form to submit each of your reviews.

What if your review is missing a video? Please use the contact information on the spreadsheet to politely remind your classmate to (i) submit their video using last week's form, and (ii) send you a copy of the link to their video. [They need to do both.]

Interviews

Postponed until next week as we wait for enrollment to finalize.

Extra Credit

Extra credit this week: in the Tuesday lecture we talked about the "Stop To Think 14.4" problem: An ice cube is floating in a glass of water that is filled entirely to the brim. When the ice cube melts, the water level will (a) fall, (b) stay the same, (c) rise and cause the water to spill.

For extra credit: do this experiment and prepare a brief presentation with your results. The amount of extra credit depends on the quality of the submission, up to the value of the week's explainer videos.

Submit using the extra credit form. No due date, but you'll get more credit if you submit this week.

Explainer Video Assignments

This week we'll continue to assign videos by section. You will have two videos to create this week.

DIS (Sec 003): W 12:00 - 12:50pm

DIS (Sec 005): W: 5:00 - 5:50pm

Update (1/14): for problem #68, please do part (a) and (c), you may cite the solution to part (b), which I append below. This should help keep your explainer within 5 mins.

The solution to part (b) is as follows. You do not have to derive this in your explainer video and can simply cite the solution. You can say in your video that you're given the solution for part (b).

DIS (Sec 006): F: 8:00 - 8:50am

DIS (Sec 008): F: 10:00 - 10:50am

Neat links

These links are outside the scope of our course, but they're still neat.

Use the UCR VPN to access journals off campus.

Barotrauma: "The effects of underwater pressure on the body" Neosha S Kashef, TEDEd
- Blog post "The Physics of Scuba Diving and Decompression Sickness," by Grace VanValey, 2016
Spinal disc herniation (Wikipedia), in relation to Problem 70 in Knight
Why do melting icebergs raise the sea level?
"Melting icebergs boost sea-level rise," Kate Mcalpine, New Scientist, 30 April 2010
Traffic as a fluid
- Wikipedia: Traffic Flow
- "An Analysis of Traffic Flow," Harold Greenberg, Operations Research Vol 7 p. 79 (1959)
Flow
- There are several neat laminar flow videos on YouTube. (See below.)
- If you ever want to start a fight with engineers or physicists, you can bring up why the Bernoulli principle by itself does not explain why airplanes fly. The snarky way to do this is to say, "oh yeah? Then why can airplanes fly upside down?"
  - "No One Can Explain Why Planes Stay In The Air," Ed Regis, Scientific American, February 2020
  - An answer from physics.stackexchange (15981)
  - A neat explainer-of-an-explainer from Fermat's Library: "How Airplanes Fly," Anderson and Eberhardt.
  - Energy cost of flight, Sanjoy Mahajan, American Journal of Physics, October 2020

Old materials

Videos from Spring 2020

These are old recordings from the Spring 2020 version of this course. You are welcome to watch them for additional background.

Intro to fluids (pdf)

W02_topic1.mp4

Hydrostatics (pdf)

W02_topic2.mp4

Buoyancy (pdf)

W02_topic3.mp4

Fluid dynamics (pdf)

W02_topic4.mp4

Page updated

Report abuse