Alex Barr

Continually embarrassed of my graduate Alma mater @universityoftexas.bsky.social. I certainly won’t consider any donations until the spineless leadership is kicked to the curb.

Thanks for the heads up! Big bummer.

Newton's cradle ornament would be fun.

I refer to "centripetal acceleration" for any curved path. I remember thinking v^2/r only applied to UCM so I try to emphasize that it is more general but that there may also be tangential acceleration.

When labeling axes, I usually say radial axis but sometimes say centripetal axis. I never use the term centripetal force other than once to explain why we never need that term (it's not a force, it's just the name people give to ΣF in the radial direction). I try to emphasize it's still just ΣF=ma.

For the roller coaster at top I would say we know there is centripetal acceleration toward the center of the circle so ΣF=mv^2/r. When the coaster is between top and bottom I would say there is centripetal acceleration and tangential acceleration and I would draw tangential and radial axes.

I emphasize that centripetal force is just a name for the sum of radial forces and not a type of force. I really like your phrase of calling it a job description. I use radial and centripetal interchangeably when describing axes or acceleration.

2025 AAUP Faculty in the South Survey The Georgia conference of the American Association of University Professors [AAUP] and its partners in states across the South have been at the forefront of fighting attacks on higher education. To as...

👀 The 2025 @aaup.org Faculty in the South Survey is for professors in Virginia, North Carolina, South Carolina, Georgia, Florida, Tennessee, Kentucky, Alabama, Mississippi, Louisiana, Arkansas, or Texas. Ends 8/29 at 5pm Eastern.

docs.google.com/forms/d/e/1F...

K-State physics professor: Federal cuts in science research threaten Kansas, America | Opinion ‘If we pull back now, we don’t just slow innovation; we hand the future to our competitors.’

Great op-ed on the importance of federal investment in research by Dr. Bharat Ratra. Great example of showing how investment pays dividends to the local community. @standupforscience.bsky.social

www.kansas.com/opinion/gues...

At the university, I only briefly touch on either topic. I point out that drift velocity is slow and energy flows through the circuit must faster than charges move. Current density I mention because we do a lot with charge density, but I don't actually use current density.

NO! VOTE NO!

A black and white photo of Vera Rubin measuring spectra

Vera Rubin has been selected to be featured on the back of a quarter. She is the first astronomer to be honored this way. Read about her research on the Andromeda galaxy and how it led to the discovery of dark matter in this article written by Rubin herself. doi.org/10.1063/1.24...
🔭 #WomenInStem

I’ve heard deconstructive so much I started to think maybe that is the word.

I’m driving from Fort Worth to Austin tomorrow to Stand Up for Science! Join your local rally and take a stand for discoveries, economic growth, curing diseases, and understanding the universe. Science is inclusive and we want to include you!

I'll be at the protest in Austin!

Congress: Save Medicaid Now Politicians are attempting to pass devastating cuts to Medicaid right now and we must act fast. Send a message telling your member of Congress to fight back now.

URGENT: The House is set to vote tomorrow on whether to advance $880 billion in cuts to Medicaid — eviscerating essential programs that provide lifesaving services for people with disabilities, children, seniors, and more.

Tell your representative now: Don't cut Medicaid.

Given how often students misuse a calculator and fail to recognize their result makes no sense I have no confidence in their ability to accurately assess LLM results

I’ve done this before successfully, but last semester the cup of dyed water flew through the air and crashed down on a table. Very memorable for students.

I haven't read them, but E.F. Taylor wrote some papers about introducing action in intro physics, www.eftaylor.com/leastaction....

trinket: run code anywhere Teach using Web VPython.

One of my intro students made a nice model of a falling Slinky, trinket.io/glowscript/2... press z to drop the Slinky. #iTeachPhysics

This week a S asked what is energy. I borrowed from Feynman and said it’s the universe’s version of money - something made up that’s useful for bookkeeping.

www.walter-fendt.de/html5/phen/s... helps visualize how the counter propagating waves pass in and out of phase. Like Michael, I think of coherent as applying to a wave source rather than to two different waves.

Sure. Here are the slides I use. drive.google.com/file/d/1lAGW...

I like to ask this saying a box falls on the cart and they move together. Ss solve it same as you show and then I ask if there is any friction in the problem. One of my favorite Qs. Scott’s Q will make a great pairing next time I do that.

Universal gravitation. Tomorrow is orbits and PE. After that we will do calculations for NASA’s DART mission.

Told my students about this effort and just once and a handful of them wrote Nr as units on the exam.

Cool. I have these as postcards but didn’t know there was a book. The postcards are great to give out in class instead of extra credit.

Fun question. My argument isn't as rigorous, but I say r^-1.9 because the orbit doesn't close. The path is just a little too wide at the end of each "ellipse" so gravitational force must be just a little too weak.