In this (one-minute) video clip, Neil Degrasse Tyson claims that a football game was won because at the final field goal, the flight path of the kicked ball was affected by the rotation of the earth.
Now, Tyson is a famous professor of astrophysics, and I am not.
But I think he is wrong.
The ball was kicked , and just barely flew between the goal posts, after touching one of them.. But as I understand Newton’s laws…it doesn’t matter that the earth (and hence the goalposts) were moving.
The entire setup is one, closed system: the ball, the football field, the goal posts, the player who held the ball, and the player who kicked the ball. They are all rotating along with the earth, so relative to each other there is no horizontal motion right or left. It doesn’t matter if the ball is on the ground, or flying through the air…its path from the player’s foot towards the goal is determined only by the direction of the kick, and not changed by the earth’s rotation.
Yes, a flying ball can be affected by Coriolis force, like any ballistic missile. But for a football kick this effect is negligible, unless you are Superman.
B..b..b,b,b..but in my high-school level physics class, all the problems at the end of each chapter said to ignore friction, assume that pulleys were connected by weightless strings, etc, etc.
I am neither a mathematician nor a physicist. But this feels right to me:
The sum total of my knowledge on this comes from history books, from which I learned that artillery gunners were finding their shots landing off target by 100-120 yards or so at a distance of 25 miles, give or take. And I also know that the Coriolis effect compounds based on range and speed.
There ends the sum total of my knowledge.
Based on that much, though, my gut feeling is that a small, comparatively slow football over a typical fifty yard ballistic arc isn’t going to deflect more than a fraction of an inch. Wind and spin will be more significant, I bet.
I welcome correction of my ignorance by smarter people.
Well,….he does say it was likely “aided” and he does say 1/3 of an inch….which satisfies your statement. Like a scientist, he does not say “it was caused by,” That’s one of those leaps that people might infer, even though he doesn’t imply it.
Basic problems in introductory physics implicitly assume Galilean invariance, or that all objects in the problem are in a common inertial reference frame; that is, that external accelerations are applied as a fixed function of orientation and distance between bodies without respect to velocity or position within the frame. So, whether you throw a ball up into the air at a pole or at the equator with the same initial conditions it will describe the same planar arc. (And because introductory textbooks assume a ‘flat’ gravitational field it will be a parabola instead of an ellipse, which is a reasonable approximation for the distance that a person can throw a ball.)
However, rotating reference frames like the surface of the Earth make this more complicated because objects are under differential acceleration which varies with respect to position and velocity within the rotating frame, so it matters at what latitude and direction of a moving object on a (quasi-)spherical surface. For the ‘man throwing a football’ problem the effects are negligible but for fast moving objects like rockets (and in theory hypervelocity bullets fired at long range targets) or predicting the large scale fluid dynamics if the atmosphere it is actually an important influence.
Tyson is (somewhat hyperbolically) making an example to describe a principle that is pretty subtle and requires some vector calculus to really understand mthemarically but he’s not wrong.
So at the very limit there can be ball trajectories that would miss on a non-rotating planar earth, but would be a successful goal on the real rotating Earth. And likewise on the other post in that same goal.
So in effect when viewed from the kicker’s POV, they need to aim about 5mm = 0.2 inches left or right of where they see the uprights to be in order to drive the ball between them. Even a magically perfectly straight kick will have a slight hook or slice due to Coriolis. And whether it deviates left or right is fixed by the location and orientation of the stadium. But deviate it will.
Clearly any breeze in the stadium will have a larger effect.
My overall bottom line: NdGT is technically correct. Which is the worst kind. Pick an inapt example, and prove something pointless about it. It amounts to anti-learning.
Don’t forget that this also affects kick length as well. Consider a ball in a non-rotating FoR that hits the crossbar and just deflects back onto the field for a missed attempt, but is given a tiny fraction of an inch more oomph in a rotating environment and makes it over the crossbar on the doink.
Physics minutia is always fun, but NDT is basically wrong. For all he knows the kicker took the effect into account already, and just muffed it. I mean, he’s aiming for the middle, not the goalpost! I think he’s already missed!
Did NDT take into account the fingerprint grease on one side of the ball? Hmm? QED ipso facto I rest my case.
I surely agree that someone who correctly understands Coriolis force, rotating reference frames, and all the rest has a better, more nuanced, understanding of physics than someone who’s never heard of those things.
Where that falls off the rails is when the audience takeaway is just that “stuff curves significantly in a wacky way because mumbo jumbo”. So going forward they can blame close calls (good or bad) on these sorta-secret subtleties. That kind of thinking is bad. And IMO science popularizers have a duty to actively try to minimize people going off on those tangents.
I’m not hugely fond of “lies to children”, but for many purposes I’d rather the authority figures explain the base case, then say (ref @Just_Asking_Questions just above), “there are a bunch more subtleties, but they each, and collectively, amount to negligible differences in this circumstance. They exist, but they’d detract from your takeaways from my explanation of football kicks.”
Ah, the doink! Great thing, a doink, but beware of doing it to a cow. Talking from a friend’s experience. NDT, on the other hand, has a doink coming his way. He gets on my nerves.
I was being a bit snarky, but my point is like you said, I think: the macro differences outweigh the micro effects. Coriolis effects didn’t make the filed goal successful; the bad kick almost made it unsuccessful.
eta: the kicker probably subconsciously already allows for the effect. Allowing for it doesn’t help when you miss that far.
