Phunny Physics III

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Mushtang

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So I have a few of these kinds of things I've come up with over the years.

A standard train that's moving down the tracks in one direction always has a small percentage of it's mass moving in the opposite direction, no matter how fast the train is moving. This doesn't refer to parts of the train that are moving slower but still in the same direction, but to a portion of the train that is actually moving in the other direction relative to the ground.

True story?
 

Ravenex

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This is not necessarily true. There may be components of the engine moving fast enough toward the back of the train to be going backward relative to the ground, but if the train is going sufficiently fast they won't be. The slowest moving part of the train with respect to the ground is the infinity thin line of wheel between the axel and where it meets the ground, which unless the train is sliding, is stopped relative to the ground.

 
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Mushtang

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This is not necessarily true. There may be components of the engine moving fast enough toward the back of the train to be going backward relative to the ground, but if the train is going sufficiently fast they won't be.
It is true, no matter how fast the train goes.
 

BuiltFromTrash

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Fuel or exaust flow?? Rotating engine parts might count, but that is not constant.
 

Ravenex

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Are you referring to atomic scale things? Like vibrations in atoms and molecules? If so it could be a large fraction of the mass that has an instantaneous velocity in the other direction. But, I didn't think that is what you were getting at. Please explain your reasoning.
 

Zeus-cat

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This is not necessarily true. There may be components of the engine moving fast enough toward the back of the train to be going backward relative to the ground, but if the train is going sufficiently fast they won't be. The slowest moving part of the train with respect to the ground is the infinity thin line of wheel between the axel and where it meets the ground, which unless the train is sliding, is stopped relative to the ground.

There would be parts of the drive train, I am specifically thinking of gears, that would be rotating just like the wheel. Given the likely high RPM that they would be rotating at they would be traveling at a net negative forward motion for part of their revolution.
 

Incongruent

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That part is the photons shining out from the rear lights.
 

ThirstyBarbarian

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This is not necessarily true. There may be components of the engine moving fast enough toward the back of the train to be going backward relative to the ground, but if the train is going sufficiently fast they won't be. The slowest moving part of the train with respect to the ground is the infinity thin line of wheel between the axel and where it meets the ground, which unless the train is sliding, is stopped relative to the ground.

However, that is not how a train's wheel is designed. There is a flange on the wheel that hangs BELOW where the wheel meets the track. That bottom part of the flange goes backwards. The top part of the flange is always moving FORWARD faster than the train. There may be other internal parts of the engine that are moving back and forth much faster than the train is ever moving on the track.
 

Mushtang

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However, that is not how a train's wheel is designed. There is a flange on the wheel that hangs BELOW where the wheel meets the track. That bottom part of the flange goes backwards. The top part of the flange is always moving FORWARD faster than the train. There may be other internal parts of the engine that are moving back and forth much faster than the train is ever moving on the track.
Bingo! The flange of the steel wheels that is below the top of the track does indeed move backwards.


Edit to add this image I just found online.

 
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Ravenex

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Bingo! The flange of the steel wheels that is below the top of the track does indeed move backwards.


Edit to add this image I just found online.

I stand corrected, I had thought briefly about the flange but hadn't done the analysis fully.
 

dr wogz

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What if Mary Tyler Moore is standing on a flat car of said train, and does her famous 'hat toss'.. Does she catch her hat? negating any wind resistance or any silly bird, or that she tossed it while : Under a bridge, in a tunnel.. Assuming it is a straight toss 'up' ..
 

Zeus-cat

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No, she's dead so she can't toss her hat in the air.
 

adrian

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No, she's dead so she can't toss her hat in the air.
Alright, so zombie Mary Tyler Moore attempts the same hat toss - does she catch it?

Answer: no, because being a zombie, she barely has enough brains to figure out which way is up, let alone remember to catch the hat again on the way down.

Or:
Let's travel back in time to when Mary Tyler Moore was alive, put her on the flat car, and have her do the hat toss - does she then catch the hat?

Answer: no, because we're neglecting air resistance, and the only way that happens is if we're in a vacuum. Mary Tyler Moore may have been alive at the start of the experiment but she's dead now due to asphyxiation.
 

ThirstyBarbarian

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Alright, so zombie Mary Tyler Moore attempts the same hat toss - does she catch it?

Answer: no, because being a zombie, she barely has enough brains to figure out which way is up, let alone remember to catch the hat again on the way down.

Or:
Let's travel back in time to when Mary Tyler Moore was alive, put her on the flat car, and have her do the hat toss - does she then catch the hat?

Answer: no, because we're neglecting air resistance, and the only way that happens is if we're in a vacuum. Mary Tyler Moore may have been alive at the start of the experiment but she's dead now due to asphyxiation.
Oh my God! I knew she had passed away, but I never heard how! Was she really asphyxiated in a hypothetical thought experiment?
 

Mushtang

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Oh my God! I knew she had passed away, but I never heard how! Was she really asphyxiated in a hypothetical thought experiment?
If I remember correctly the cause of her death was never conclusively identified. There WAS a zombie there, falling hats, a locomotive, so it could have been a lot of things. It makes sense that she suffocated but that may just be the easy to believe story. Some say she was dead before the air was removed. It just depends on which hypothetical thought experiment you actually believe.
 
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