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Ask a physicist anything. (3)

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laconicstudent

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Could someone of 19 or younger please just click the link on this quote and correct the girl who doesn't understand simple concepts like Gravitation? It is agonizing.

I got out my astronomy book that I used all this year just to review so things so I'll be ready when school starts back. Upon doing so I ran into some things I had hi-lighted (and wrote small LOL out to the side or contradictions on certain pages. (Whether in the book or by scientific observation and reasoning.)

One of the LOL(/contradiction) I've run into says "Scientists try to form hypotheses that explain how nature works. If a hypothesis is contradicted by experiment or observations, it must be revised or discarded."

I just thought so you mean that if I said that I have a sample of E. Coli in a jar and I form a hypotheses that states "This E. Coli will eventually turn into Lactobacillus with just adaptation and time. That hypothesis would be discarded if it never happen?" and the answer is of course yes. "Then why do scientist still teach us that a single-celled micro bacterium turned into multi-celled bacterium and eventually formed all the life we see today if we've never actually observed a single-celled bacterium become a multi-celled bacterium?"

This LOL moment also lead to see the first huge contradiction (even though this section is before the part listed above) it states "There was no light for the first 400 million years, until gravity was able to pull some of the gas together to form the fist stars."

Well we've never observed gravity randomly in space all the gravity seem to be created because the star is already there. So doesn't that mean that you have already contradicted a hypothesis and that it needs to be revised or discarded?

I'm only on Chapter one now, I'll post more as I read on so stay tuned. ( And please don't have people come in here saying "You don't understand how science works." (or something to the effect.) I'm getting this straight from a text book so if you want to complain to someone call Michael A. Seeds or Dana E. Beckman...)

I hate it when people deliberately post stuff in restricted forums to avoid being corrected.
 
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Wiccan_Child

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Arglebargle. This is my response to her.

I got out my astronomy book that I used all this year just to review so things so I'll be ready when school starts back. Upon doing so I ran into some things I had hi-lighted (and wrote small LOL out to the side or contradictions on certain pages. (Whether in the book or by scientific observation and reasoning.)
Lulz.

One of the LOL(/contradiction) I've run into says "Scientists try to form hypotheses that explain how nature works. If a hypothesis is contradicted by experiment or observations, it must be revised or discarded."
Yep.

I just thought so you mean that if I said that I have a sample of E. Coli in a jar and I form a hypotheses that states "This E. Coli will eventually turn into Lactobacillus with just adaptation and time. That hypothesis would be discarded if it never happen?" and the answer is of course yes.
No. If your hypothesis is that E. coli will turn into lactobacillus, then how do you know it won't happen if you don't wait another day? In the case of evolution, these things take millions of years.

Of course, evolution doesn't say one species evolves into another, pre-existing species. Evolution says they evolve into completely new species.

"Then why do scientist still teach us that a single-celled micro bacterium turned into multi-celled bacterium and eventually formed all the life we see today if we've never actually observed a single-celled bacterium become a multi-celled bacterium?"
Because the evidence supports this hypothesis. There isn't a shred of evidence to the contrary; I challenge you to cite any.

This LOL moment also lead to see the first huge contradiction (even though this section is before the part listed above) it states "There was no light for the first 400 million years, until gravity was able to pull some of the gas together to form the fist stars."
Yep.

Well we've never observed gravity randomly in space all the gravity seem to be created because the star is already there. So doesn't that mean that you have already contradicted a hypothesis and that it needs to be revised or discarded?
No. Your astonishing lack of understanding as to the nature of gravity doesn't mean you've refuted the entire field of astrophysics.

Gravity is when stuff pulls on stuff. The more stuff there is in a particular place, the harder the pull. That's why black holes are so powerful: there's an awful lot of stuff very very close together, which has a very strong pull.
Light formed 400 million years ago because a) before that, there were no stars, and b) after that, there were. The first stars formed when gas slowly pulled itself together in little clumps, which then pulled more gas in, and more and more, until it was so dense that it began to undergo thermonuclear fusion (basically, its what makes the Sun bright and hot). Thus, there was light.

I'm only on Chapter one now, I'll post more as I read on so stay tuned. ( And please don't have people come in here saying "You don't understand how science works." (or something to the effect.) I'm getting this straight from a text book so if you want to complain to someone call Michael A. Seeds or Dana E. Beckman...)
You don't know how science works. If you think you've found a contradiction between your understanding of science and the textbook, it's almost certainly an error on your part: Seeds and Beckman, who I assume wrote the book, are probably much smarter than either of us. Obviously, it's not unheard of for a textbook to be wrong, especially if it's a) out-of-date, or b) a small typo. But major things like that, no, I don't think you've overturned the entire field of cosmology and astrophysics.

Instead of declaring it a contradiction (LOL), why not simply ask someone to explain it for you?
 
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Maxwell511

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No. If your hypothesis is that E. coli will turn into lactobacillus, then how do you know it won't happen if you don't wait another day? In the case of evolution, these things take millions of years.

Of course, evolution doesn't say one species evolves into another, pre-existing species. Evolution says they evolve into completely new species.

Because the evidence supports this hypothesis. There isn't a shred of evidence to the contrary; I challenge you to cite any.

Poppycock. Next thing you will be telling the girl that hydrogen (given enough of it and enough time) can turn into people.
 
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Wiccan_Child

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Poppycock. Next thing you will be telling the girl that hydrogen (given enough of it and enough time) can turn into people.
People have Hydrogen in them, so, by the commutative property of multiplication, Hydrogen is People. Thus the reason God destroyed the Hindenburg!
 
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Maxwell511

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People have Hydrogen in them, so, by the commutative property of multiplication, Hydrogen is People. Thus the reason God destroyed the Hindenburg!

Did you just prove God's existence?

My mind is blown.
 
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corvus_corax

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Take a roughly spherical hunk of ice, about the size of an USA standard baseball.
What upward wind speed would support that (i.e. what upward wind speed would prevent it from falling to the Earth's surface)?

Additionally, how much upward wind force would it take to accelerate such a piece of ice upwards?

Just curious, as I'm trying to imagine the wind forces necessary to create baseball size (or bigger) sizes of hail.

And since I'm not a physicist, I thought I'd ask one of our resident ones :)
 
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Maxwell511

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Take a roughly spherical hunk of ice, about the size of an USA standard baseball.
What upward wind speed would support that (i.e. what upward wind speed would prevent it from falling to the Earth's surface)?

Depends on the height of the ball in the atmosphere. Use this formula equated to the force due to gravity at the height you want to find the answer. Solve for u.

Additionally, how much upward wind force would it take to accelerate such a piece of ice upwards?

Very little as gravity is a very weak force. Use this formula to find out for the height that you want.
 
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Cabal

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Why does it get windier in the evening?

At a guess, I'd say the temperature gradient over areas still being warmed a bit to the west and places being cooled to the east changes as the sun goes down....
 
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Wiccan_Child

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At a guess, I'd say the temperature gradient over areas still being warmed a bit to the west and places being cooled to the east changes as the sun goes down....
The change to twilight is pretty long, the gradient might be too shallow to do much. I'm thinking it's just psychosomatic, since it's darker and colder and quieter, making you more alert to odd sounds.
 
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Wiccan_Child

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Take a roughly spherical hunk of ice, about the size of an USA standard baseball.
What upward wind speed would support that (i.e. what upward wind speed would prevent it from falling to the Earth's surface)?

Additionally, how much upward wind force would it take to accelerate such a piece of ice upwards?

Just curious, as I'm trying to imagine the wind forces necessary to create baseball size (or bigger) sizes of hail.

And since I'm not a physicist, I thought I'd ask one of our resident ones :)
The force would have to counter gravity.

F = ma, a = 9.81, so F = 9.81*m, where m is the mass of the ball in kilograms.

The density ρ of ice (at 0°) is 0.9167 g/cm³, or 916.7 kg m[sup]-3[/sup].
The radius r of a baseball is about 3" in diameter, or 0.0381 m in radius.
The mass m of a spherical object of radius r and uniform density ρ is given by 4/3 πρr[sup]3[/sup].
Thus, the mass of the ball is 0.212 kg (give or take).
Thus, the force require to keep a ball aloft is F = 2.083 N.

The force with which wind blows is related to a pressure gradient:

pressure_equation1.gif


Where D is the air density (~1.29 kg cm[sup]-3[/sup]), P[sub]i[/sub] is the pressure at point i in N m[sup]-2[/sup], and n is the distance between the points in metres.

If anyone wants to use this to convert force into airspeed, be my guest ^_^
 
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Cabal

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No no, It really does get windier... If you sit outside as evening falls, the wind kicks up and sweeps through the trees and bends them all like it hasn't done during the day. Now why, people, why?

Every evening?

What's your sample size, young lady?
 
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sfs

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What matters for the baseball is not the total force of wind, but the force exerted on an object the size of a baseball. At the relevant velocities (which lie in the broad transition region to turbulent flow), wind resistance is roughly proportional to the velocity squared, but the coefficient of drag really has to be measured empirically for something as complicated as a baseball.

Oh, and the answer is 95 miles per hour, based on wind tunnel tests. (Taken from my handy copy of The Physics of Baseball, by Robert Adair. Bob Adair was a physics professor at Yale, the official physicist of the National League for several years, and my thesis advisor's advisor.)
 
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