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Author | Topic: Flat Earth Society | |||||||||||||||||||||||||||||||
CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
I was surprised to find that Neil deGrasse Tyson believes in a flat Earth. Here's what he said;
quote: Do the physics and you will find this is only true on a flat Earth. In fact, we Round Earthers believe that if a bullet is fired level fast enough (>11.2 km/s) it will never hit the ground!
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
It actually makes a bit over 1m height difference over 4084m. That should provide a measurable difference in the time it takes the bullet to reach the ground.
No rifle can fire a bullet fast enough but IF it could fire one at escape velocity plus a bit for air resistance (>11.2 km/s) then it would never hit the ground. So when you do the physics Neil deGrasse Tyson is a Flat Earther!
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
My post at Message 38 was somewhat tongue in cheek and has sparked an interesting discussion. I must admit I was surprised myself at the difference the Earth's curvature could make over a few kilometers. I wonder where we could find a flat (i.e. spherical) plain of sufficient extent to confirm this experimentally?
In a similar vein I also say Galileo was wrong in his experiment dropping weights off the leaning tower of Pisa; the heavy one should hit the ground first.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
RrHain writes:
What's the difference between doing this on the moon compared to the Earth? But then again, they did this on the moon with a hammer and a feather. The gravity is lower so they fall slow enough to be observed. There is close to a vacuum so air resistance doesn't affect the fall. Earth however has atmosphere. Two objects of different masses, same material, same shape, will fall at different rates due to air resistance. In the case of cannon balls this would only be detectable with very precise measuring equipment, such as would not have been available to Galileo, but it will make a slight difference and the heavier one will fall faster.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
Thank you Dwise1 for your detailed calculations. You have confirmed what I said; do the physics and the fired bullet will hit the ground later than the dropped one. This effect becomes more pronounced with higher muzzle velocities.
There's no reason why you can't stand on a platform to do this experiment so that the initial height could be 9.81 meters if you wanted. That would make the drop time 1 second (neglecting air resistance). The bullet will take a fraction longer to hit the ground. You could even do this on the moon and almost eliminate air resistance. The smaller radius and lower gravity will enhance the difference in fall time.The escape velocity of the moon is 2.38km/s which is getting much closer to a rifle muzzle velocity. Potentially you could produce a rifle that could fire a bullet at escape velocity on the moon.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
caffeine writes:
You're right! Turns out I can make mistakes too. Assuming no air resistance, the drop time would be closer to 1 1/2 secondss=(1/2)at^2; so the platform should be high enough to give an initial height of 4.9m. Or you can start with an initial height of 19.6m to get a 2 second drop time. Edited by CRR, : No reason given.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
NoNukes writes:
Indeed it does, which is why I said "cannon balls'. Same density, same shape, different sizes. By the way, heavy "objects hit the ground first due to air resistance" requires a lot of qualifiers. Except for a bit of variation with Reynolds Number; Drag is proportional to Dia^2 Weight is proportional to Dia^3 So the heavy one will fall faster, although as I said the difference would have been undetectable for Galileo. Incidentally, I remember seeing/hearing that Galileo was repeating an experiment performed by someone else. Good science to replicate the experiment. Edited by CRR, : No reason given.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
quote: OK, Happy now? If it wasn't Galileo then it was Simon Stevin and Jan Cornets de Groot. And if Galileo did perform the experiment then he was replicating Stevin & de Groot. However the fact remains that because the experiment took place in a fluid (air) the heavy one would fall faster due to the effects of drag. This would have produced an undetectable difference for observers in the 16th Century.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
Galileo would have been correct for objects falling in a vacuum. However in air you get air resistance which alters the results; and the faster they fall the greater the air resistance, until the object reaches terminal velocity.
Of course with objects like cannon balls of different sizes this effect is relatively small and would not have been detectable to 16th century observers. In a fluid such as air two balls connected by a string will have a mass equal to the sum of the parts but the combined object is a different shape to the the individual objects. Assuming the same shape and density;At t=0 the two balls will have zero speed and hence zero air resistance and each will start with the same acceleration. As speed increases air resistance will increase and will have relatively more effect on the smaller ball which will then fall slower than the other. When the string becomes taut it will then apply additional acceleration to the smaller ball and retard the heavier one. The combined object will then fall at a speed somewhere between that of the two balls individually. Then you get the added complication that the second ball will be in the wake of the second. The tension in the string will always have to be T>=0 otherwise they will start to separate. Conceivably you could get a combination such that the combined object will fall faster than either of the two separate objects. However, as I have said, these effects would have not been observable for 16th century observers. Similarly the inaccuracies of Newton's laws of motion were not observable until centuries later. So Galileo was wrong, Newton was wrong, and Neil deGrasse Tyson was wrong.
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
Porkncheese writes:
Must be a reference to the Lone Ranger ;-) What silver bullet? Have you seen the movie where the Lone Ranger goes to Canada? It's called "On to Toronto, Tonto, Pronto!"
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
The rays are parallel but some will pass to the left of the observer and some will pass to the right. Due to perspective these then appear to diverge from a common point.
Does that help?
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CRR Member (Idle past 2271 days) Posts: 579 From: Australia Joined: |
If you deign to respond to this post, I specifically request that you answer this one question:
Nah, it's not worth it.
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