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Natural Science Forum / Physics / General Physics / July 2008Paths against gravity and using gravity vs energy used
Two paths are created for going over a mountian. One path (path D for direct route) is a straight line to the top and a straight line to the bottom on the other side. Another path (path C for curved) is a curved path to the top and a curved path to the bottom on the other side. The distance bewteen the start of the paths to the end of them is the same and we can use a tunnel to prove such of course. So... What path would need more final energy use to follow? :)  SignatureJames M Driscoll Jr Spaceman > Two paths are created for going over a mountian. > [quoted text clipped - 8 lines] > What path would need more final energy use to follow? > :) It takes the same amount of energy whichever route is taken... E = m * g * (Height of end - height of start). Assumptions: 1) The object traversing the parth is 100% efficient. 2) We can ignore secondary effects such as the varaition in local gravity due to the mountain and the like. >> Two paths are created for going over a mountian. >> [quoted text clipped - 14 lines] > > It takes the same amount of energy whichever route is taken... So you can take a longer path with the same amount of energy as the shorter path would have needed? That won't even work on flat surfaces nevermind going up hills. It seems you have a flaw that is pretty wrong. :) Sorry. You are incorrect. > E = m * g * (Height of end - height of start). > [quoted text clipped - 3 lines] > 2) We can ignore secondary effects such as the varaition in local > gravity due to the mountain and the like. Think again please. and ignoring gravity is also a big problem. Or design a car that can do such without the 100% efficiency part and save oil for all of us. :) SignatureJames M Driscoll Jr Spaceman >>> Two paths are created for going over a mountian. >>> [quoted text clipped - 23 lines] > Sorry. > You are incorrect. No. He assumed a 100% efficient vehicle and a frictionless motion. The only thing that determines the required energy input is the maximum vertical excusion. The path taken is irrelevant. Gravity is a conservative force field. >> E = m * g * (Height of end - height of start). >> [quoted text clipped - 6 lines] > Think again please. > and ignoring gravity is also a big problem. He explicitly factored in gravity. That was the reason for calculating the required energy: E = m*g*(h1 - h2). In fact, gravity is the only pertinent factor if the car is 100% efficient and the motion frictionless. > Or design a car that can do such without the 100% efficiency > part and save oil for all of us. >>>> Two paths are created for going over a mountian. >>>> [quoted text clipped - 29 lines] > path taken is irrelevant. Gravity is a conservative force > field. He assumed an impossible trip to the top of a mountain then didn't he? As I said. He is incorrect. > He explicitly factored in gravity. That was the reason > for calculating the required energy: E = m*g*(h1 - h2). > In fact, gravity is the only pertinent factor if the > car is 100% efficient and the motion frictionless. Frictionless thought is his problem then. Whatever the problem is. He is incorrect in reality. The longer path will take more energy. simple and factual as that. :) SignatureJames M Driscoll Jr Spaceman >>>>> Two paths are created for going over a mountian. >>>>> [quoted text clipped - 34 lines] > As I said. > He is incorrect. Who is "he"? According to my newsreader you wern't replying to another post. You asked the original question. Your reply quotes stuff not in previous posts in the thread. > Who is "he"? According to my newsreader you wern't replying to another post. > You asked the original question. > > Your reply quotes stuff not in previous posts in the thread. Sorry forget that. Looks like my news server is messed up. > > Who is "he"? According to my newsreader you wern't replying to > another post. [quoted text clipped - 3 lines] > > Sorry forget that. Looks like my news server is messed up. No prob, :) >>>>>> Two paths are created for going over a mountian. >>>>>> [quoted text clipped - 37 lines] > Who is "he"? According to my newsreader you wern't replying to > another post. You asked the original question. You should look a little bit more. The replies are all there. the he is the person that replied to my original post. > Your reply quotes stuff not in previous posts in the thread. I do not see it doing such. >> It takes the same amount of energy whichever route is taken... > [quoted text clipped - 19 lines] > Or design a car that can do such without the 100% efficiency > part and save oil for all of us. Duh I'm not that stupid. Obviously in a real world problem one route might require more energy but you didn't specify the problem in sufficient detail to allow anyone to calculate which route that would be. > >> It takes the same amount of energy whichever route is taken... >> [quoted text clipped - 24 lines] > sufficient detail to allow anyone to calculate which route that would > be. OK, My point was to just show that if anything a longer path will require more energy and when you remove friction, they are pretty much equal when just fighting gravity alone. SignatureJames M Driscoll Jr Spaceman >> >> It takes the same amount of energy whichever route is taken... >>> [quoted text clipped - 29 lines] > will require more energy and when you remove friction, > they are pretty much equal when just fighting gravity alone. As usual the devil is in the details. You need to specify all the parameters to make an informed judgement. For example, the velocity profile along each path; drag effets can vary in complex ways with velocity. Moving at a snail's pace along a longer path can take much less energy than going at a high velocity along a shorter path if drag due to air friction is a factor. Air drag tends to go up as the square of the velocity. >> >> It takes the same amount of energy whichever route is taken... >>> [quoted text clipped - 29 lines] > will require more energy and when you remove friction, > they are pretty much equal when just fighting gravity alone. Thats what I meant when I wrote: "1) The object traversing the parth is 100% efficient." eg no losses due to friction, air resistance etc only gravity. >>> >> It takes the same amount of energy whichever route is taken... >>>> [quoted text clipped - 37 lines] > is 100% efficient." eg no losses due to friction, air resistance etc > only gravity. Yup, That is what I was actually looking for really. Sadly I am told otherwise that you are wrong and gravity would make the longer circular path take less energy., but I know you are not wrong so it's no big deal. Some people just don't get how energy works. :) > My point was to just show that if anything a longer path > will require more energy and when you remove friction, > they are pretty much equal when just fighting gravity alone. I believe the same applies to an metal object and a magnet. eg It takes the same amount of energy to remove a bit of iron from a magnet no mater what route you take. I believe this explains why magnetic shields don't help you build a permanant magnet perpetual motion machine. > > My point was to just show that if anything a longer path >> will require more energy and when you remove friction, [quoted text clipped - 5 lines] > shields don't help you build a permanant magnet perpetual motion > machine. Yup, It is all the great power of energy balance. energy will balance itself and there is no way you can change that force of nature permanantly. :) SignatureJames M Driscoll Jr Spaceman On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> wrote: > Two paths are created for going over a mountian. > [quoted text clipped - 12 lines] > James M Driscoll Jr > Spaceman James, it entirely depends on the energy required to dig the tunnel. Then too, I believe you know this, so 'nuff said. Harry C. > On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> > wrote: [quoted text clipped - 17 lines] > James, it entirely depends on the energy required to dig the tunnel. > Then too, I believe you know this, so 'nuff said. Of course it would.. :). But alas the tunnel is not the difference we are looking for. According to all know facts, a longer path will always take more fuel (energy) than a shorter one would as long as the paths are already there of course. But for some reason. some people want to ignore this "proven a billion upon billion times over" fact. :) SignatureJames M Driscoll Jr Spaceman >> On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> >> wrote: [quoted text clipped - 28 lines] > some people want to ignore this "proven a billion upon billion times > over" fact. It's only true for inefficient cars running their engines continuously, wasting fuel. Then you want to minimize engine time (and vertical climbs, and starting and stopping). The actual result achieved (work done) in moving the car from point A to point B, in the Physics sense, is just moving the car from one gravitational potential to another. The path taken is irrelevant unless it imposes other factors (like frictional losses). > > hhc...@yahoo.com wrote: > >> On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> [quoted text clipped - 43 lines] > > - Show quoted text - A longer curved path requires more distance if not more gravity. That extra distance makes it the less efficient. Mitch Raemsch >>> On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> >>> wrote: [quoted text clipped - 33 lines] > to minimize engine time (and vertical climbs, and > starting and stopping). Even 100% efficient engines would burn more to go further. Friction is the key still. :) > The actual result achieved (work done) in moving > the car from point A to point B, in the Physics > sense, is just moving the car from one gravitational > potential to another. The path taken is irrelevant > unless it imposes other factors (like frictional > losses). The path taken being irrelevant is a really big problem It appears you are ignorant to that non irrelevant fact. :) SignatureJames M Driscoll Jr Spaceman >>>> On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> >>>> wrote: [quoted text clipped - 49 lines] > It appears you are ignorant to that non irrelevant fact. > :) > The path taken being irrelevant is a really big problem > It appears you are ignorant to that non irrelevant fact. > :) Path length is irrelevant if you burn no fuel at all while traversing it. As I said before, in space travel there is always a fuel versus time tradeoff. You can burn a lot of fuel and get there quicker, or burn a little and take longer to get there. Either way, no one can get enough feul into space to run a high thrust engine continuously for days on end. You can, though, use micro g thrust ion engines for tiny craft. They squirt xenon gas ions out via electrostatic means. Very, very low thrust. Be prepared for long trips. >> The path taken being irrelevant is a really big problem >> It appears you are ignorant to that non irrelevant fact. >> :) > > Path length is irrelevant if you burn no fuel at all > while traversing it. OMFG Greg. I just said forget fuel, (I stated the fuel word incorrectly) Fuel is not the only energy that is being used. Replace fuel with energy. There is no way you can travel a longer path from A to B without needing more energy than the shorter path from A to B would need. Sheesh Read a little bit for once will ya? Please show a spiral path uphill or any longer path uphill from A to B that uses less energy than a shorter path from A to B would use. Otherwise. Wake up and admit you are wrong about the energy being needed to take the longer path. SignatureJames M Driscoll Jr Spaceman >>> The path taken being irrelevant is a really big problem >>> It appears you are ignorant to that non irrelevant fact. [quoted text clipped - 13 lines] > Sheesh > Read a little bit for once will ya? James. If you want to draw such distinctions then use the correct terminology. Use either Kinetic Energy (KE) or Potential Energy (PE) or Mechanical Energy (ME), which is the sum of the two (ME = KE + PE), or energy supplied by fuel (FE) which can add to the ME. For motion in a conservative field, like gravity, where no other forces are involved, the total energy expended or extracted by motion from point A to point B in that field is the same regardless of the path taken. Note that this does not say that the energy budget during the trip is the same (KE versus PE), only that by the end of the trip, when everthing is totaled, the net energy difference between the starting point and the ending point will be the same. If you do something silly during the trip along a path, like lose energy to friction that has to be replaced by burning fuel and can't be recovered, or just burning fuel for the hell of it, then that is a different matter since external forces are being introduced. If you just follow the terrain in the field and employ only 100% efficient means of moving, then any energy you put into the vehicle, say to climb over obstacles, you will get back as kinetic energy (you burn energy to climb a hill, but you get it back as an increase in velocity as you descend again). Any such energy you needed to put in to the system to travel your path you will retain (as KE) when you arrive at point B. > Please show a spiral path uphill or any longer path uphill > from A to B that uses less energy than a shorter path from > A to B would use. > Otherwise. > Wake up and admit you are wrong about the energy > being needed to take the longer path. The minimum energy required corresponds to the potential energy difference between the bottom and top of the hill. The energy wasted traversing an arbitrary path with inefficient vehicles does not change that. For your request I choose to use ballistic trajectories to get from the bottom of the hill to the top. In the first case I lob a cannon ball with just enough energy so that it just reaches the top when it reaches its apogee (the top of its trajectory). It follows a long, arced path. Next I attempt to shoot the cannon ball in a straight line to the top. I find that, no matter *how* much gunpowder I use, I just can't get the ball to fly perfectly straight. It always curves somewhat due to gravity. I figure that I can add an extra motor to the cannon ball to keep it flying straight. But now I need to launch the motor and its fuel along with the canon ball! That requires more energy then firing the canon ball alone, more than for the case where I just lobbed the ball alone. Now the ball and motor is fired at the mountain top with a similar velocity as the first cannon ball so it can reach the top in less time (you do want the straight path to take less time, right?), and the motor is run all the way and aimed downwards to give a constant thrust of 1g to exactly counter the 1g due to gravity. Now the ball travels a straight line as desired, but I've used *more* than the same energy than the lobbed ball just to launch it, then I had to burn fuel in the motor all the way just to keep the trajectory straight. Travelling on the Earth's surface and making relatively minor vertical excursions for the most part, we tend to think that "straight lines" are always best because they use less fuel because our car engines run continuously, friction saps energy, and a straight line will take less time. Travelling on what is essentially a flat plane for short distances, the natural least resistance path for an object to follow is a straight line. We come to think of this as a rule of nature, and it is true enough when no major changes in elevation are involved. But roll a ball on the side of a hill and it won't naturally travel in a straight line, it'll follow an arc. That's the least resistance (inertial) path in that case. It requires no additional fuel (energy input) to follow that path. Making it follow a straight line under those circumstances would require energy input. In space you can forget friction and having a convenient surface to hold onto to keep you from falling and to allow you to manouver by grabbing onto and pushing or pulling against. Every manouver that takes you from an inertial path requires payment in terms of fuel. >>>> The path taken being irrelevant is a really big problem >>>> It appears you are ignorant to that non irrelevant fact. [quoted text clipped - 25 lines] > expended or extracted by motion from point A to point > B in that field is the same regardless of the path taken. Greg, Do the experiment. Please. You are actually stating conservation of energy is wrong. point A to B against gravity needs more energy if the path is longer simply because of the time difference that they are rolling for. Again, Try the dang experiment. and see for yourself. the curve path wil take longer and need more energy to fight the gravity than the shorter path will. > The minimum energy required corresponds to the potential > energy difference between the bottom and top of the hill. > The energy wasted traversing an arbitrary path with > inefficient vehicles does not change that. The energy difference will be affected by the amount of time you are fighting the gravity in your longer path. Conservation of energy is wrong if such is not true. :) Sadly you really are saying that driving a car up a hill on a longer path will use less energy than a straight line path would. That is really sad Greg. really sad. Try it as stated or not. I could care less now. You never want to try the way stated anyways because you never want to ever prove yourself wrong.. So why would you now. :) SignatureJames M Driscoll Jr Spaceman > According to all know facts, a longer path will always take > more fuel (energy) than a shorter one would as long as the paths are > already there of course. Not true. Drag is proportional to the square of velocity so a constant speed route can take less energy than one that involves a variable speed. Even if the constant speed route is longer. My reply is irrelevant though because your problem is badly specified. > > According to all know facts, a longer path will always take >> more fuel (energy) than a shorter one would as long as the paths are [quoted text clipped - 4 lines] > variable speed. Even if the constant speed route is longer. My reply > is irrelevant though because your problem is badly specified. I am sorry, I meant to include if traveling at the same speed. same speed longer path = more fuel than same speed shorter path. On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> wrote: > Two paths are created for going over a mountian. > [quoted text clipped - 7 lines] > So... > What path would need more final energy use to follow? Your curved path just happens to coincide with my orbit. I am not wasting fuel to decelerate and negotiate your tunnel. See: http://en.wikipedia.org/wiki/Center_of_mass Sue... > :) > > -- > James M Driscoll Jr > Spaceman > On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> > wrote: [quoted text clipped - 13 lines] > orbit. I am not wasting fuel to decelerate and > negotiate your tunnel. You must have forgetten the fuel used to get to your "orbit". and the tunnel path is not in question. since it actually uses the least fuel of all and laughs at both the other paths completely. :) SignatureJames M Driscoll Jr Spaceman On Jul 5, 5:27 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> wrote: > > On Jul 5, 3:40 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> > > wrote: [quoted text clipped - 16 lines] > You must have forgetten the fuel used to get to > your "orbit". I am orbiting the sun yea as I read your silly postings. I have yet to receive a bill from the fuel company for the ride. Sue... > and the tunnel path is not in question. > since it actually uses the least fuel of all and laughs [quoted text clipped - 4 lines] > James M Driscoll Jr > Spaceman > On Jul 5, 5:27 pm, "Spaceman" <space...@yourclockmalfunctioned.duh> > wrote: [quoted text clipped - 22 lines] > silly postings. I have yet to receive a > bill from the fuel company for the ride. nice twist, but .. it is only true because nature does not bill you since it all occured before you got here you are just hitchin the ride for free. But any fool knows the orbit did not occur without energy being used to do such. And if you had to pay for the energy needed to place Earth into this orbit you would be bummin. Nevermind the energy needed to place Solar System in the Galaxy etc.. :) |
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