Alan Nathan

Alan Nathan

@pobguy.bsky.social

Professor Emeritus of Physics, U of Illinois. Physics of Baseball: baseball.physics.illinois.edu. Mostly post about baseball. Sometimes Con Law, basketball, physics, WW1, Twilight Zone, ...

2K followers251 following787 posts

Alan Nathan
@pobguy.bsky.social

In the California case, how about the anti-comandeering doctrine.

Rick Hasen@rickhasen.bsky.social

The Major Questions Doctrine Alone Should Doom DOJ’s Lawsuits in Both Alaska and California:Congress Would Not Hide Broad Federal Powers over State Elections in A Law Making Noncitizen Voting a Misdemeanor or in General Language in Registration Statute’s Preamble electionlawblog.org/2026/the-maj...

electionlawblog.orgThe Major Questions Doctrine Alone Should Doom DOJ's Lawsuits in Both Alaska and California: Congress Would Not Hide Broad Federal Powers over State Elections in A Law Making Noncitizen Voting a Misde...There are so many things wrong with the federal government’s attempts to meddle in state election processes in Alaska and California, but this post highlights just one point: the DOJ’s ridiculous atte...

Alan Nathan reposted

Michael McFaul
@mcfaulmike.bsky.social

Trump’s actions toward Russia and Ukraine have left me deeply troubled. I've discussed why in several interviews, along with broader questions about autocrats, democrats, and U.S. foreign policy. Listen to these recent podcast conversations here: michaelmcfaul.substack.com/p/trump-puti...

michaelmcfaul.substack.comTrump, Putin, and the Question of Whose Side America Is OnFive recent conversations on Ukraine, autocracy, and U.S. foreign policy.
Alan Nathan
@pobguy.bsky.social

Vik Amar wrote a recent article about the constitutionality of the DOJ effort. Definitely worth reading his very clear discussion of the relevant issues. verdict.justia.com/2026/10/20/w...

verdict.justia.comWhy the Trump Administration’s Most Recent Legal Attempts to Pressure California Election Officials Concerning Alleged Noncitizen Voting Are Likely to FailUC Davis Law professor Vikram David Amar discusses the federal government’s lawsuit seeking an emergency injunction to bar California election officials from counting federal ballots cast next month b...
Marc Elias@marcelias.bsky.social

The Department of Justice (DOJ) is considering filing lawsuits against additional states before or after the midterms as part of its effort to force states to investigate alleged noncitizens on their voter rolls, according to an NBC News report. www.democracydocket.com/news-alerts/...

democracydocket.comReport: Trump DOJ considers suing more states to control ballot counting, before or after the midtermsCalifornia automatically mails ballots to registered voters. Seven other states — Colorado, Hawaii, Nevada, Oregon, Utah, Vermont and Washington — as well as Washington, D.C., also conduct all-mail el...
Alan Nathan
@pobguy.bsky.social

👍

Tangotiger@tangotiger.com

Seam-Shifted Wake, explained in two sentences: The seam is a bump in the road that knocks the flow of air off the ball A specific seam orientation will have that flow more to one side than the other, causing the ball to move in some direction more than it otherwise would #SSW

Alan Nathan
@pobguy.bsky.social

Just watched the Broadway production of Come From Away on Apple TV. I had never seen it before. It was fabulous! There's a local production currently playing that I hope to see. Sold out but I'm on a waiting list.

Alan Nathan
@pobguy.bsky.social

Invaders From Mars really terrified me as a 9-yr old. As a teenager, I saw the movie again, found it laughable, and could not understand how I had found it so scary. As an adult, I saw the movie yet again. While I still found it laughable, I understood how it could be so frightening to a child.

Alan Nathan@pobguy.bsky.social

Invaders From Mars was very scary to a 9-yr old boy (me!).

Alan Nathan
@pobguy.bsky.social

Let me back off my last claim. Comparing April to July, the increase in distance is due roughly in equal parts to the decrease in Cd and the increase in temperature.

Alan Nathan@pobguy.bsky.social

So the variation of distance is due in part to variation in Cd (which is ball-related) and in part to variation in air density (mainly temperature). The total monthly variation is huge, from 392.5 ft in April to 405.0 in July, and most of that variation is due to Cd rather than temperature.

Alan Nathan
@pobguy.bsky.social

Followup on my drag analysis. Plots below show monthly-average fly ball distance for narrow range of EV,LA. Top graph is plotted vs average Cd. But Cd alone does not determine drag. Bottom graph is plotted vs. average air density-corrected Cd. Much more clear-cut correlation, as I would expect.

Alan Nathan
@pobguy.bsky.social

So the variation of distance is due in part to variation in Cd (which is ball-related) and in part to variation in air density (mainly temperature). The total monthly variation is huge, from 392.5 ft in April to 405.0 in July, and most of that variation is due to Cd rather than temperature.

Alan Nathan reposted

PBS News
@pbsnews.org

On 9/11, the passengers of Flight 93 stormed the cockpit, forcing the hijacked jet to crash in Shanksville, Pa. Before the world knew of their bravery, members of the D.C. Air National Guard were prepared to make their own sacrifice. Heather Penney shares her story. https://to.pbs.org/3UKF9Wv

to.pbs.orgFighter pilot reflects on order to sacrifice herself to stop Flight 93 on 9/11On 9/11, the passengers of United Airlines Flight 93 stormed the cockpit, forcing the hijacked jet to crash in Shanksville, Pennsylvania. But before the world knew of their bravery, members of Washing...

Alan Nathan reposted

Karin Wulf
@kawulf.bsky.social

Elle Cordova on fonts is one of the great joys of social media.

Elle Cordova@ellecordova.bsky.social

I am the very model of a modern day typographer A font take on the tune “Modern Major General” by Gilbert & Sullivan #typography #fonts #graphicdesign

Alan Nathan
@pobguy.bsky.social

Paying homage to one of my heroes: Statue of Muhammad Ali in Lewiston ME, site of the 2nd Clay-Liston fight in 1965. I listened to the radio broadcast of that fight as no home TV was available.

Alan Nathan
@pobguy.bsky.social

Vik Amar is my go-to guy for constitutional issues (I took his Con Law class a few years ago). His latest writing addresses discrimination based on age in voting vis a vis the 26th Amendment. See his clear explanations here, drawing parallels to 15A and 19A verdict.justia.com/2026/08/24/b...

verdict.justia.comBipartisan Panel of Fourth Circuit Judges Reaches the Right Result (for the Right Reasons) in Twenty-Sixth Amendment Case, Grant v. Belangia, Setting up Possible Supreme Court Review of a Circuit Spli...UC Davis Law professor Vikram David Amar discusses the Fourth Circuit’s decision in Grant v. Belangia, which invalidated a South Carolina law restricting automatic absentee voting to seniors and creat...
Alan Nathan
@pobguy.bsky.social

BRT, for a typical topspin grounder, the friction between ball and dirt reduces the forward speed of the ball, as one expects. But it also *increases* the topspin, sometimes making it difficult to field cleanly.

Alan Nathan@pobguy.bsky.social

For foultip to speed up, the topspin rate would have to be of order 18,000 rpm...clearly not realistic. For a topspin grounder at 100 mph to speed up, the topspin rate would have to exceed about 11,000 rpm, which is also unrealistic.

Alan Nathan
@pobguy.bsky.social

For foultip to speed up, the topspin rate would have to be of order 18,000 rpm...clearly not realistic. For a topspin grounder at 100 mph to speed up, the topspin rate would have to exceed about 11,000 rpm, which is also unrealistic.

Alan Nathan@pobguy.bsky.social

Same reasoning applies to a topspin grounder, which can gain speed if the spin is large enough so that the surface speed points backwards.

Alan Nathan
@pobguy.bsky.social

For a foultip, the ball skims the top surface of the bat. The resulting force on the ball is due to sliding friction and is opposite to the relative ball-bat velocity at the surface. If the ball had a *huge* amount of topspin, the surface speed would be forward and the force would be backward.

Kelly Blidook@kblidook.bsky.social

Out of interest, is there any way that contact with something that is moving perpendicular or opposite to the direction of the ball could increase its speed in its original direction - ie. by increasing its spin, etc?

Alan Nathan
@pobguy.bsky.social

Under such (unrealistic) conditions, the foultip would be moving faster than the original pitch (and the spinrate would be smaller). So, it is possible in principle for the ball to speed up but not physically realizable.

Alan Nathan
@pobguy.bsky.social

My wife did similar gaze training last year to help combat bouts of vertigo. It really works.

Trevor Magnotti@illegalscreens.bsky.social

This is called gaze training, we use it all the time in concussion rehab. It’s part of the Visual Occulomotor Screen (VOMS) I use to diagnose concussion and it trains the pathway from the eyes to the visual cortex. Looks stupid, is actually useful.

Alan Nathan
@pobguy.bsky.social

Nice work. Sportvision developed Command f/x back in 2011, as discussed at the Pitch f/x summit that year. See share.google/7r4Ky4JA2F9m.... It was never very successful.

share.googleRecap of the SportVision Pitch F/x SummitResearch often inspires more questions than it answers. That’s acceptable because asking the right questions is such an important part of doing the right research. Every presentation at SportVision’s…
Pitch Profiler@mlbpitchprofiler.com

Introducing the Intended Location Tracker! Command has needed computer vision and a ball tracking unit. Now it takes two taps and a phone. Chart where a pitch was meant to go and where it actually finished, and the gap between them becomes a report.