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chris l.
2003-Apr-22, 11:42 AM
In the 'Ripley's Believe it or Not' section of the newspaper a coupa days ago, it stated that a Swedish physicists have determined that a curve ball on Mars would move in the opposite direction to a curve ball on Earth. I don't understand this. Could someone explain it to me?

Reacher
2003-Apr-22, 11:48 AM
Ok, i should know this, but i have 2 excuses: im Australian, and i dont get out much. Whats a curve ball?

Also, i envy you. you get ripleys in the paper? i only get to watch it on T.V. When im off school.

Eta C
2003-Apr-22, 12:52 PM
A baseball pitch that has a curved trajectory. There is some debate about the precise reason why, but the general consensus is as follows. The pitcher applies spin to the ball when he throws it. This causes an aerodynamic force similar to the lift on an airplane to push the ball to one side. A good reference to all of this is the book "The Physics of Baseball." The author's name eludes me now, but I'll get the link in a bit.

As to why it should be different on Mars, I have no idea. I think I believe it not.

Reacher
2003-Apr-22, 12:59 PM
Thanks for that, Eta.

I dont beleive it either. We had to learn all this stuff over the past 2 years in aeronautics, and i have a rather deep understanding of it, so i really find it impossible for that to occur.i can understand why on earth the curve ball moves in that direction, but on mars, theres no reason for its course to differ.

Eta C
2003-Apr-22, 01:12 PM
OK. "The Physics of Baseball" by Robert Adair. Besides the physics of various pitches, he also goes into explanations of hitting. A short book, but an interesting description of practical physics.

chris l.
2003-Apr-22, 01:41 PM
I understand the physics of a curve ball. I can throw one. What I don't understand is why it would move in a different direction on Mars.

Tzuk_Te
2003-Apr-22, 02:16 PM
Who knew that Tycho Brahe, besides destroying geocentrisim, can also through a curve?

The big question: Are you left handed?

Back to "The Physics of Baseball" on pg. 18-19, Adair says this about Denver: "A 400-foot drive by Dave Winfield in New York would go as much as 40 feet farther through the thinner air in Denver! Furthermore, pitchers would find that their fast balls were half a foot quicker in Denver though their curves would not bite quite so well."

I'm assuming Martian atmospheric density at "sea" level is still somewhat less than even Denver. I think a curve ball would probably be ineffective on Mars, but I don't know why it would curve opposite of one Earth?

Tzuk Te

kilopi
2003-Apr-22, 04:00 PM
Quick google on "curve ball Mars" gave me this space.com webpage (http://www.space.com/scienceastronomy/mars_curveballs_030221.html) that explains it. The second returned link was a Nature webpage (http://www.nature.com/nsu/030217/030217-11.html) that applied it to David Beckham's famous bend.

Reacher
2003-Apr-22, 05:31 PM
I know its from a reputable site, but I fail to beleive it.

kilopi
2003-Apr-22, 05:41 PM
I'm a little dubious myself, but I don't have two years of background in aeronautics like you do, what part do you not believe?

tracer
2003-Apr-22, 05:54 PM
Tzuk_Te quoted pp. 18-19 of The Physics of Baseball as saying:

Furthermore, pitchers would find that their fast balls were half a foot quicker in Denver
I had no idea that a foot was a unit of velocity or time.

russ_watters
2003-Apr-22, 06:01 PM
Thanks for that, Eta.

I dont beleive it either. We had to learn all this stuff over the past 2 years in aeronautics, and i have a rather deep understanding of it, so i really find it impossible for that to occur.i can understand why on earth the curve ball moves in that direction, but on mars, theres no reason for its course to differ. Yeah. The aerodynamics are the same everywhere. With lower gravity there is less arc and with thinner air there is less curve. Its as simple as that.

kilopi
2003-Apr-22, 06:08 PM
Yeah. The aerodynamics are the same everywhere. With lower gravity there is less arc and with thinner air there is less curve. Its as simple as that.
Actually, I thought those two articles I referenced earlier explained the idea fairly well. What is it that you disagree with?

Tzuk_Te
2003-Apr-22, 06:22 PM
I had no idea that a foot was a unit of velocity or time.

I didn't either. I take this to mean that, in the same period of time, a fastball in Denver will have travelled 6in. farther than a fastball at sea level.

Tzuk Te

kilopi
2003-Apr-22, 06:27 PM
I didn't either. I take this to mean that, in the same period of time, a fastball in Denver will have travelled 6in. farther than a fastball at sea level.
I've seen reports about how a particular runner was "a step quicker" than another runner. Could be the same sort of thing. After all, what are the units of quickness? :)

traztx
2003-Apr-22, 06:36 PM
Yeah. The aerodynamics are the same everywhere. With lower gravity there is less arc and with thinner air there is less curve. Its as simple as that.


Exerpts from here (http://www.space.com/scienceastronomy/mars_curveballs_030221.html)...

Magnus Force

A spinning object creates a whirlpool of air around it. On the left side of a curveball, this whirlpool is moving in the same direction as wind that's zipping past the ball, generating increased air speed. On the right side, the whirlpool opposes the oncoming wind, slowing it down.

As any airplane wing designer knows, faster-moving air means less pressure (wings are designed to make air move more quickly over the top, thus providing lift). With our curveball, the left side experiences less pressure than the right side, pulling the pitch to the left.

The phenomenon is called Magnus force.

The whirlpool threshhold

In thin air, however, the whole whirlpool process breaks down if the distance a molecule must travel to hit another molecule is greater than the diameter of the spinning object. In this case, another process governs the ball's movement.

Now, sans a whirlpool, our intended curve ball interacts directly with incoming air.

The interaction is simple physics in that case. This makes perfect sense to me. The artical goes on to say that this is not just a Martian phenominum:



The reverse-Magnus-effect can even occur on Earth, Essen said, with very tiny "macro-molecular" objects. And while the study examined objects moving at small velocities, Essen figures there is reason to believe that it will govern things at higher speeds and thus be relevant for re-entry of spacecraft.

chris l.
2003-Apr-22, 07:49 PM
Does this mean that there is an atmosphere, something between the atmosphere on Earth and the atmosphere on Mars, that would cause a STRAIGHT curve ball?

Reacher
2003-Apr-22, 10:09 PM
i can see what they mean.
i didnt read the nature article, partially because it wouldn't open. :)

i concede that i cant think up anything to counter it...

Damn!

im gonna pull a Hoagland and say i will beleive it when i have seen it.

to draw attention away from the fact that i was just proven wrong -without any proof- im going to comment on the fact that this smiley looks so evil!!
:) :) :) see!?!?! it wants to kill you!!!

David Hall
2003-Apr-22, 10:32 PM
to draw attention away from the fact that i was just proven wrong -without any proof- im going to comment on the fact that this smiley looks so evil!!
:) :) :) see!?!?! it wants to kill you!!!

Hmm. You may have something there. It does bear a passing resembleance to the Smiling Man (http://www.userfriendly.org/cartoons/smilingman/). Coincidence?

See here (http://ars.userfriendly.org/cartoons/?id=20030316&mode=classic) also.

Reacher
2003-Apr-23, 01:04 AM
Hey, i think i like it ...smiling man, smiling man...

That could be like a mafia warning. You go into a forum, click the top topic, and see :) . from this, you cant tell that either:
A) The trenchcoat mafia has marked you for death.
B) Scott's trying to get his 'posts' number up, so is posting random, nonsensical things everywhere.

BigJim
2003-Apr-23, 01:16 AM
I also did not understand it at first, but that space.com article straightened me out. If you have a little trouble understanding it, try this alternate explanation:

Whereas the curve ball on Earth will curve to the side it is spinning to, such as curving right for counterclockwise motion (the "view from the top" really helps here)


Quote:
A spinning object creates a whirlpool of air around it. On the left side of a curveball, this whirlpool is moving in the same direction as wind that's zipping past the ball, generating increased air speed. On the right side, the whirlpool opposes the oncoming wind, slowing it down.

As any airplane wing designer knows, faster-moving air means less pressure (wings are designed to make air move more quickly over the top, thus providing lift). With our curveball, the left side experiences less pressure than the right side, pulling the pitch to the left.

The phenomenon is called Magnus force.


On Mars, think of the ball as having almost no atmospheric reactions, but instead, curving to the right due to the torque from the counterclockwise spin.

Reacher
2003-Apr-23, 01:33 AM
Torque? im not so sure thats the correct term for the mars conditions.

BigJim
2003-Apr-23, 01:47 AM
Nothing to do with the atmospheric conditions. Torque is still torque. Angular acceleration is proportional to the force times the lever arm. This prduct is called the moment of inertia or "torque", indicated with the Greek letter tau. (That's not it, but I wanted to have some symbol anyway :) )

Reacher
2003-Apr-23, 04:43 AM
but I don't have two years of background in aeronautics like you

not to brag, but its actually 4 years, we just started studying this particular thing 2 years ago, is all.

Reacher
2003-Apr-23, 04:46 AM
Exactly, torque is still torque. torque has nothing to do with the atmosphere, so it isnt responsible for the difference.

beskeptical
2003-Apr-23, 09:17 AM
Bigjim: ".....torque. Angular acceleration is proportional to the force times the lever arm."

Hmmmm. A spinning bullet or football goes straighter. But then that would be with a spin angle perpendicular to the forward motion, (if perpendicular is the right term for that but you know what I mean). So without the impact of unequal air pressure created by the dynamics of the throw and the atmosphere, would the spin direction create a curve ball if it were spinning parallel to the forward motion?

Logic tells me the ball would still go straight because for all the spinning pulling it to one side there should be equal spinning pulling it back to the other side.

But I'm not too sure of this. I also would have thought the ball curving differently on Mars did not sound logical until I read the above explanation.

Tzuk_Te: "Who knew that Tycho Brahe, besides destroying geocentrisim, can also through a curve?"

Throw, as in I can throw a ball through the window.

Sorry to bring it up if it was just a space case error. I make those all the time.

russ_watters
2003-Apr-23, 01:43 PM
Hmmmm. A spinning bullet or football goes straighter. But then that would be with a spin angle perpendicular to the forward motion, (if perpendicular is the right term for that but you know what I mean). So without the impact of unequal air pressure created by the dynamics of the throw and the atmosphere, would the spin direction create a curve ball if it were spinning parallel to the forward motion?

Logic tells me the ball would still go straight because for all the spinning pulling it to one side there should be equal spinning pulling it back to the other side. Spinning stabilizes flight in air - it keeps airflow consistent. Your interpretation is correct.

russ_watters
2003-Apr-23, 01:56 PM
The whirlpool threshhold

In thin air, however, the whole whirlpool process breaks down if the distance a molecule must travel to hit another molecule is greater than the diameter of the spinning object. In this case, another process governs the ball's movement.

Now, sans a whirlpool, our intended curve ball interacts directly with incoming air.

The interaction is simple physics in that case. This makes perfect sense to me. The artical goes on to say that this is not just a Martian phenominum:



The reverse-Magnus-effect can even occur on Earth, Essen said, with very tiny "macro-molecular" objects. And while the study examined objects moving at small velocities, Essen figures there is reason to believe that it will govern things at higher speeds and thus be relevant for re-entry of spacecraft. What I'm not getting is why the diameter of the ball and the distance the molecules must travel to hit other molecules matters. It doesn't explain that.

It also doesen't go into this action-reaction thing: the spinning of the ball sends particles moving away from it, yes - but that depends on drag. With less pressure there is less drag. Or are they talking about the inertia of the molecules causing the friction? Thats an extrordinarily difficult thing to calculate and depends on the surface properties of the object (as does skin friction drag for that matter).

Action-reaction certainily is simple physics. But we aren't talking about perfectly elastic collisions here. Otherwise the ball wouldn't curve at all. SOMETHING must be causing uneven collisions - airflow.

kilopi
2003-Apr-23, 02:01 PM
Thats an extrordinarily difficult thing to calculate and depends on the surface properties of the object (as does skin friction drag for that matter).
And probably why we don't find the whole calculation at space.com :)

They appear to have done the calculations, though.

Tzuk_Te
2003-Apr-23, 02:06 PM
Tzuk_Te: "Who knew that Tycho Brahe, besides destroying geocentrisim, can also through a curve?"

Throw, as in I can throw a ball through the window.

Sorry to bring it up if it was just a space case error. I make those all the time.

Doh! I hope Tycho can throw a curveball better than I can spell... :)

tracer
2003-Apr-23, 09:43 PM
I doubt Tycho Brahe is able to throw a curveball very well at all, considering that he's been dead for over 3 centuries.

tvelocity
2003-Apr-24, 12:53 AM
When they mention the "whirlpool" effect in their article, I think they are referring to the effects of laminar airflow around the baseball, that is, the fact the air will be moving more in the same direction and speed as the aerodynamic surface the closer you get to that surface. Think of the baseball as having its own "atmosphere" that rotates as the ball rotates. The article on Space.com is saying that the low atmospheric pressure on Mars would reduce the laminar flow to negligible levels, leaving only the effects of simple newtonian physics to govern the interaction between the air molecules, and the surface of the ball. These effects would probably be almost too small to measure, unless the ball were rotating at speeds no human could possibly impart to it. Batter up!