Engineering question
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harold aptroot wrote:
a toy car is on a conveyor, you push it forward and the conveyor goes backward "at the same speed" (whatever that means, which is not quite clear). Can you push it forward?
Yes, but you might want to rethink about the problem. Derek Muller was able to show that multiple physics professors at prestigious universities didn't even understand the basic underlying principles. A Physics Prof Bet Me $10,000 I'm Wrong It's not exactly the same problem, in the video the propeller will generate a greater force and the vehicle will move forward. Increasing the speed of the conveyor belt will result in an even greater vehicle speed. The wheels are irrelevant. So are university degrees. :-\ Best Wishes, -David Delaune
Randor wrote:
Derek Muller was able to show that multiple physics professors at prestigious universities didn't even understand the basic underlying principles.
Along that note, here is one of the worst offenders I've ever seen. Robert Benfer, an anthropology teacher at Missouri, effectively says that once the sun sets, the sky immediately gets dark. Search for the phrase: "Our simulation for that latitude..." I've uploaded an outline of the sky back then at 22° sun depression, highlighting the fox he is talking about. The only way you could say the tail was visible is if you weren't taking twilight into account. If you are going to be studying the astronomy of ancient cultures, understanding twilight should be pretty high on the list of things to comprehend. :laugh: :laugh: :laugh: He even failed to understand when I pointed it out to him. :doh: “And because scientists are first and foremost human beings, they’re loathe to change their theories or their minds because of mere data.” - Glen Hodges
Our Forgotten Astronomy | Object Oriented Programming with C++
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Randor wrote:
Derek Muller was able to show that multiple physics professors at prestigious universities didn't even understand the basic underlying principles.
Along that note, here is one of the worst offenders I've ever seen. Robert Benfer, an anthropology teacher at Missouri, effectively says that once the sun sets, the sky immediately gets dark. Search for the phrase: "Our simulation for that latitude..." I've uploaded an outline of the sky back then at 22° sun depression, highlighting the fox he is talking about. The only way you could say the tail was visible is if you weren't taking twilight into account. If you are going to be studying the astronomy of ancient cultures, understanding twilight should be pretty high on the list of things to comprehend. :laugh: :laugh: :laugh: He even failed to understand when I pointed it out to him. :doh: “And because scientists are first and foremost human beings, they’re loathe to change their theories or their minds because of mere data.” - Glen Hodges
Our Forgotten Astronomy | Object Oriented Programming with C++
Hmmm, I don't know much about this one. I was curious as to what you're talking about. I looked it over and the article is referenced from another source: Sullivan W. (1996). The Secret of the Incas: Myth, Astronomy, and the War Against Time. Three Rivers Press, New York. Using my ever-improving Wikipedia editor skills, I checked that book beginning on page 41. The reference is based on references from yet another source and I quote 'from a discussion with Gary Urton'. Looks like Gary Urton is guy to contact on this. He probably has alot of free time[^]. Btw that guy has great credibility, you should check to see if there is something you missed.
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Quote:
Sorry, I'm tired of reading the nonsense you wrote.
Stiff upper lips: I'm never wrong... I'm tired to reading your nonsense and I'm wondering why CP let your nonsense trough
Enough, guys.
cheers Chris Maunder
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
Many years ago at a tiny company where we consumed our lunches together at the conference table we had a similar heated discussion this time re/ if you walked up a down escalator w/o changing your elevation did you do any work? I now can not imagine why this was so perplexing at the time. Then there is Richard Feynman wondering if one can piss whilst upside down. Below is my "Signature" apologies if offends My sympathies to the SPAM moderator "I once put instant coffee into the microwave and went back in time." - Steven Wright "Shut up and calculate" - apparently N. David Mermin possibly Richard Feynman “I want to sing, I want to cry, I want to laugh. Everything together. And jump and dance. The day has arrived — yippee!” - Desmond Tutu “When the green flag drops the bullshit stops!” "It is cheaper to save the world than it is to ruin it." "I must have had lessons" - Reverend Jim Ignatowski / Christopher Lloyd "Dripping water hollows out stone, not through force, but through persistence." - Ovid, Roman poet Personal Web Page https://mypaltrythoughts.blogspot.com/[^]
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Hmmm, I don't know much about this one. I was curious as to what you're talking about. I looked it over and the article is referenced from another source: Sullivan W. (1996). The Secret of the Incas: Myth, Astronomy, and the War Against Time. Three Rivers Press, New York. Using my ever-improving Wikipedia editor skills, I checked that book beginning on page 41. The reference is based on references from yet another source and I quote 'from a discussion with Gary Urton'. Looks like Gary Urton is guy to contact on this. He probably has alot of free time[^]. Btw that guy has great credibility, you should check to see if there is something you missed.
Sorry, I must not have been clear. Sullivan's book outlined how the fox's tail had became invisible due to the precession of the equinoxes on the morning of winter solstice in 650 AD. The pic I uploaded shows the sky with a sun depression of 20° (I believe) at that time. The 'fox' was a Milky Way 'object,' as it wasn't a constellation in those terms (if memory serves me correctly). The Milky Way disappears from the sky slightly before astronomic dawn, so the Milky Way would have started disappearing shortly after that 20° depression, if not at that 20° depression. Benfer, in his article, was arguing that the Milky Way and the 'fox's tail' was clearly visible in the sky, because he didn't take twilight into account. In other words, he was saying that the sky instantly goes from dark enough to see the stars, to instantly light once the sun breaches the horizon. Therefore the 'fox' could be seen all the way up to sunrise. Which is utter nonsense. Does it make sense that way?
Our Forgotten Astronomy | Object Oriented Programming with C++
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
Thanks everyone for your replies, the links and the videos. When I posted this question, little did I imagine that it would raise such an intense discussion. Thanks once again.
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Sorry, I must not have been clear. Sullivan's book outlined how the fox's tail had became invisible due to the precession of the equinoxes on the morning of winter solstice in 650 AD. The pic I uploaded shows the sky with a sun depression of 20° (I believe) at that time. The 'fox' was a Milky Way 'object,' as it wasn't a constellation in those terms (if memory serves me correctly). The Milky Way disappears from the sky slightly before astronomic dawn, so the Milky Way would have started disappearing shortly after that 20° depression, if not at that 20° depression. Benfer, in his article, was arguing that the Milky Way and the 'fox's tail' was clearly visible in the sky, because he didn't take twilight into account. In other words, he was saying that the sky instantly goes from dark enough to see the stars, to instantly light once the sun breaches the horizon. Therefore the 'fox' could be seen all the way up to sunrise. Which is utter nonsense. Does it make sense that way?
Our Forgotten Astronomy | Object Oriented Programming with C++
David O'Neil wrote:
Does it make sense that way?
Yes, I fully understood your position on the subject. Not sure if I want to get involved in your academic debate with that guy. I would be willing to play the straw man with you:
Straw Man wrote:
Is the altitude at sealevel in your astronomy software? The Andes are at nearly 7000m at the peak. A quick calculation tells me that you would be able to see approximately 300km over the horizon from the Andean mountain peaks at that elevation.
Not my argument, just trying to generate a position for you to defend. :) Best Wishes, -David Delaune
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David O'Neil wrote:
Does it make sense that way?
Yes, I fully understood your position on the subject. Not sure if I want to get involved in your academic debate with that guy. I would be willing to play the straw man with you:
Straw Man wrote:
Is the altitude at sealevel in your astronomy software? The Andes are at nearly 7000m at the peak. A quick calculation tells me that you would be able to see approximately 300km over the horizon from the Andean mountain peaks at that elevation.
Not my argument, just trying to generate a position for you to defend. :) Best Wishes, -David Delaune
The only way to find out is to go there and see for ourselves when the Milky Way disappears before sunrise. Or have a very, very good model of atmospheric absorption vs temp at that time of year, yada, yada, yada. Even at 7000m, I know it won't be visible ten minutes before sunrise, which is what he was saying. Go to street view. Here is Machu Picchu: [Google Maps](https://www.google.com/maps/@-13.163738,-72.5448503,2a,75y,81.9h,112.19t/data=!3m6!1e1!3m4!1sr5yCHd2XEJCzg0Lh3RVF2Q!2e0!7i13312!8i6656). The horizon is just more mountains.
Our Forgotten Astronomy | Object Oriented Programming with C++
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The only way to find out is to go there and see for ourselves when the Milky Way disappears before sunrise. Or have a very, very good model of atmospheric absorption vs temp at that time of year, yada, yada, yada. Even at 7000m, I know it won't be visible ten minutes before sunrise, which is what he was saying. Go to street view. Here is Machu Picchu: [Google Maps](https://www.google.com/maps/@-13.163738,-72.5448503,2a,75y,81.9h,112.19t/data=!3m6!1e1!3m4!1sr5yCHd2XEJCzg0Lh3RVF2Q!2e0!7i13312!8i6656). The horizon is just more mountains.
Our Forgotten Astronomy | Object Oriented Programming with C++
David O'Neil wrote:
The only way to find out is to go there and see for ourselves
Looks like Dr. Bromberg from the University of Toronto has a neat little tool that will calculate civil, nautical, and astronomical twilight values for arbitrary dates. The Kalendis Calendar Calculator[^] Plug in your dates/coordinates and let's have a look at the values. Best Wishes, -David Delaune
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David O'Neil wrote:
The only way to find out is to go there and see for ourselves
Looks like Dr. Bromberg from the University of Toronto has a neat little tool that will calculate civil, nautical, and astronomical twilight values for arbitrary dates. The Kalendis Calendar Calculator[^] Plug in your dates/coordinates and let's have a look at the values. Best Wishes, -David Delaune
I wrote a script for Stellarium to do that. You can view (an old version of?) it here: [Stellarium Scripting](https://github.com/Stellarium/stellarium/issues/766). The picture I posted is at 20° sun depression I believe, which is 2° greater than astronomic dawn. If you want my most recent version (which may be exactly the same as that - I haven't looked at it in a while), I'll post it.
Our Forgotten Astronomy | Object Oriented Programming with C++
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
The speed of the wheels is irrelevant - they aren't powered or driven in any way. The speed of the airflow over the wings is the source of lift, along with the wings angle of incidence. Assuming the conveyor is moving at the same speed (but in the opposite direction) as the aircraft would be on a normal runway then the aircraft would actually be stationery and the airflow over the wings would effectively be zero and thus not generating any lift?
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
The airplane does or does not lift off owing to the upward airflow forces on the wings. If the air does not move relative to the airplane (or vice versa) the plane will stay on the ground. And the speed of the conveyorbelt relative to the air close by will cause some drag, therefore some lift, but it is likely to be way too little, unless you add a quite signifant ventilator to help. That should be pretty obvious, but I miss the joke - if there is one?
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
Only if you have a really big fan blowing at a speed at least that of the aircrafts V2 (take off) speed. :laugh:
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Only if you have a really big fan blowing at a speed at least that of the aircrafts V2 (take off) speed. :laugh:
Then the aircraft will go and hit that fan :-)
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
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It obviously can since propulsion for airplanes is provided by i/e a jet engine. Airplane doesn't accelerate using wheels, like i/e a car. Conveyor belt would only make the wheels spin faster, and that's it.
Actually ... no. The conveyor will have an effect and can increase lift - slightly - since it will also drag the air along with it and if that interacts with the wings it effectively act like the plane is going faster. (That's why aircraft carriers always launch steaming full ahead into the wind when launching and recovering aircraft - it adds a few MPH to their airspeed and reduces the chances of a stall.)
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!
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Actually ... no. The conveyor will have an effect and can increase lift - slightly - since it will also drag the air along with it and if that interacts with the wings it effectively act like the plane is going faster. (That's why aircraft carriers always launch steaming full ahead into the wind when launching and recovering aircraft - it adds a few MPH to their airspeed and reduces the chances of a stall.)
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!
Your answer is confusing. First, you say: actually no, then continue with a reasonable explanation on why some extra lift would be achieved. So, airplane WOULD take off, which I assume was the point of the q. Whether it'd have more lift or no due to conveyor belt is a minor detail. There's also the matter of how long the conveyor belt is. If it's as long as the runway, then yea, but if it's as long as the airplane, airplane could fall off and probably crash in front of it.
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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ... Can the airplane take off?
The ONLY way the airplane can take off is if the speed of air respect of the airplane's speed is equal to the minimum speed the airplane needs to take off when the wind is absolutely calm. That is, because the conveyor makes the plane to be static respect to the ground, the only way the plane will take off is if there is a really hard hurricane that accelerates de wind to the plane's take off speed.
