Mike Smith Cosmos Posted May 16, 2015 Author Posted May 16, 2015 (edited) Forces on inclined slopes ... mean forces and surfaces can meet at any angle and still yield some sort of analysable result. Your tube could be facing some degrees forward of radial and your lizard might still climb out of the tube. c[/url] Yes. You will see when I finally manage to upload. My enthusiasm and nervous behaviour made a slight bias toward a forward of radial thrust, and as you say , the lizard still shot out at a ' high rate of knots ' I have solicited the cooperation of another park goer , a large black dog walker . He demonstrated to me his ' dog ball slinger ' again it uses a part circle umpf to translate circular ( 1/4 circle ) motion into a ball trow of incredible distance . This is not quite the same principle as the tube , none the less relating some form of circular inertia into centri... Motion Mike Edited May 16, 2015 by Mike Smith Cosmos
swansont Posted May 16, 2015 Posted May 16, 2015 SwansonT, How do you get an instantaneous force if the definition of a Newton is the force required to move a kg one meter per second per second? Don't you need some time for the mass to move at a certain rate? Or in our circular example, you need the thing to change direction. How can you change direction instantaneously? Calculus F = dP/dt. In most situations (mass is constant) this is F=ma, which is F = m dv/dt Toss a ball up in the air, and it comes back down. At the apex, the change in direction is instantaneous. There is only a single, infinitesimally short instant that it has v = 0 In our merry-go-round example and our motor bike example we have humans experiencing an outward pull. This, I think perhaps is experienced over time, and is not an instantaneous judgment. No, we don't. You experience the illusion of an outward pull. It is experienced over time. The value is instantaneous, but the effect is continual. I read somewhere that a human moment is about a second and a half, long. It makes a certain amount of sense to give humans at least a few tenths of a second to make a determination that requires signals to come from their inner ear, and nerves in their arms and signals from their eyes, and motor pulses to be sent to the various muscles attempting to keep the human from falling and hurting themselves. Seems a person would lean to keep from falling off or falling over. The direction he/she would lean would be away from the direction they thought they were going to fall. If they were feeling the instantaneous force, they would lean out, to gain their balance. They don't lean out. I have never felt the urge to lean out when riding a bike around a corner. I don't know from where you get such a notion. I also think you're wrong about the length of time it takes to get these signals. The situation, over time, is that your inertia is taking you out, away from the center. Tangential to the circle. "Out" to me, implies radially. Like you said, the tangential motion is increasing your distance from the center. You are not so concerned with forces, as much as you are concerned with where you are going to go, if you grip fails. By the time you realize you are being pulled East, you are already being pulled North, or for a more reasonable example, if you broke the circle into the 15 degree segments we were talking about on the space station, and you were to ask the person to call out which of the 24 directions she was facing and which of the directions she felt she was being pulled in, I would bet she would lag the proper call by at least a few sections, since it takes time to sense and vocalize. Such slop should be considered when trying to figure why we feel we are being pulled in a certain direction. Regards, TAR That's really a question of physiology and not physics. This is a physics discussion. The tube keeps the mass going at the same omega (rotational velocity). As it travels outward it is being accelerated by the tube but only in a tangential direction. It needs a centripetal force to hold it in a circular motion but the mass's centrifugal force, that would have acted at the center, is not attached to the center, so it accelerates the mass to the exit end of the tube. There is no outward force acting on the object. Repeat 100 times. Maybe it will begin to sink in. If there is a centrifugal force, what is providing it? Friction is in the opposite direction of motion along the tube, (i,.e inward; it's the centripetal force) and the walls provide a normal force, which is tangential to the circle. What, physically, is pushing out on the object? And still like doing practical experiments ! With cardboard carpet rolls and toy lizards. ( I still wish I knew how to upload my I pad video , only 20 sec long , ) but the lizard shoots out the top with a mixture of tangent and outward inertia . It's worth seeing . In the tube it's restricted to going totally radially upwards and outwards away from the centre. And if you viewed it while being attached to the inside of the tube it would be a straight radial line ! If you uploaded it there would be a chance of analyzing it and showing you that no such thing is happening.
Robittybob1 Posted May 16, 2015 Posted May 16, 2015 (edited) .... If there is a centrifugal force, what is providing it? Friction is in the opposite direction of motion along the tube, (i,.e inward; it's the centripetal force) and the walls provide a normal force, which is tangential to the circle. What, physically, is pushing out on the object? ... We both agree it will progress "radially" spiralling along a path up the tube. What pushes it? Obviously it must be the lack of the centripetal force, for it would need that to travel in the circle. Friction will provide a meagre centripetal force but soon the inertia overcomes the friction and it begins sliding along the tube. Gaining speed tangentially and radially, nothing pushes it but the motion itself can be concentrated into a fluid pressure as in a centrifugal pump. The reason it gains speed tangentially is because it is going slower than the walls of the tube at the ever increasing radius. The reason it speeds up radially is that even though the tangential speed is proportional to the radius the force required to it make travel in a circle goes up too but the friction stays the same so the ratio of friction:required centripetal force decreases. Edited May 16, 2015 by Robittybob1 -1
swansont Posted May 16, 2015 Posted May 16, 2015 We both agree it will progress "radially" spiralling along a path up the tube. What pushes it? You need to learn Newton's laws of motion before you do anything else involving mechanics. Without that, you can't possibly understand what's going on. A force is not necessary to keep something moving. The object is already moving, so no force is needed. There is no force. Obviously it must be the lack of the centripetal force, for it would need that to travel in the circle. The absence of a force is not a force. Friction will provide a meagre centripetal force but soon the inertia overcomes the friction and it begins sliding along the tube. Gaining speed tangentially and radially, nothing pushes it but the motion itself can be concentrated into a fluid pressure as in a centrifugal pump. No force is needed. Correct. The reason it gains speed tangentially is because it is going slower than the walls of the tube at the ever increasing radius. Partly right. The linear speed of the tube is wr, where w is the rotational speed, so that increases with r. The object is going at the same speed as the walls, not slower. However the walls need to exert a force to speed it up. The reason it speeds up radially is that even though the tangential speed is proportional to the radius the force required to it make travel in a circle goes up too but the friction stays the same so the ratio of friction:required centripetal force decreases. It's not obvious to me you could tie that ratio to the speed.
Robittybob1 Posted May 16, 2015 Posted May 16, 2015 (edited) .... A force is not necessary to keep something moving. The object is already moving, so no force is needed. There is no force. The absence of a force is not a force. No force is needed. Correct. Partly right. The linear speed of the tube is wr, where w is the rotational speed, so that increases with r. The object is going at the same speed as the walls, not slower. However the walls need to exert a force to speed it up. Did you look at those YTs on centrifugal motion? When the weights are close into the center of rotation there isn't the required velocity to orbit at the larger radii. There has to be an acceleration in the YT (and in our case within the tube) . That acceleration will take a force, it increases its tangential speed as it moves outward to keep up with the walls. It is in the tube so it can't go slower than the wall true, but it still has to speed up as it moves away from the center. You seem to agree with that. You agree that that acceleration is going to require a force? (your words "the walls need to exert a force to speed it up" but before that you say there is "no force".) The absence of a force is not a force. I was showing how much force will be required to stop it on its outward path. It will take a force as large as its required centripetal force (calculable using mv^2/r) to make it attain a circular motion. It's not obvious to me you could tie that ratio to the speed. I tested that ratio to the tangential speed many times in an Excel spreadsheet, and I graphed radius to the centripetal force. As the radius increases the required centripetal force increases linearly too. Friction between the wall and the mass is constant. So the ratio of Fc:Friction is not constant. Speed is proportional to radius at a constant omega (w). That part is definitely right. Today I hope to observe the angle the mass exits the tube by experiment. Is it tangentially (Swansont) or at an angle to the tangent as I suspect? I think we can see "the angle to tangential" effect with the last ball as it rises to meet up with the others. (1:36 onward.) Look at how the last ball rising up the incline catches up to the others. The balls don't just keep on rising up out of the bowl either. The inclined slope and gravity combine to provide the force to stop their outward motion at that rotational speed. I didn't see you try and explain what overcomes the friction. Thought experiment: You're sitting on a stationary merry-go-round and then some kids come and start spinning it. Your friction allows you to stay on to begin with but later you begin to slide. What pushes you? Now I'm asking you the same question as you asked me. What force overcame the force of friction? It is not the centripetal force; for friction is the centripetal force. Edited May 16, 2015 by Robittybob1
Robittybob1 Posted May 16, 2015 Posted May 16, 2015 (edited) I've just come in from the experimentation and the mass definitely leaves the tube at an angle to the tangent, somewhere between the tangent and the radial depending on the rotational velocity. This was observed and confirmed by my friend as well. (Something like as if it is leaving at a tangent to a smaller circle earlier in the rotation.) Edited May 16, 2015 by Robittybob1
pzkpfw Posted May 16, 2015 Posted May 16, 2015 ... Thought experiment: You're sitting on a stationary merry-go-round and then some kids come and start spinning it. Your friction allows you to stay on to begin with but later you begin to slide. What pushes you? Now I'm asking you the same question as you asked me. What force overcame the force of friction? It is not the centripetal force; for friction is the centripetal force. "What pushes you?" : Nothing. There is no force "pushing" you. "What force overcame the force of friction?" : Your inertia. As the merry-go-round spins, your inertia means your body wants to keep going in a straight line. The friction with the surface allows a centripetal acceleration to be applied, that keeps you going in the circle. As it speeds up, it's harder to keep you going in that circle. The force of the friction is not enough and you start to slide (outwards, it seems, but essentially trying harder and harder to go in a straight line). The centripetal force is no longer enough to counter the inertia. It's the same answer. Again and again.
swansont Posted May 16, 2015 Posted May 16, 2015 When the weights are close into the center of rotation there isn't the required velocity to orbit at the larger radii. There has to be an acceleration in the YT (and in our case within the tube) . That acceleration will take a force, it increases its tangential speed as it moves outward to keep up with the walls. It is in the tube so it can't go slower than the wall true, but it still has to speed up as it moves away from the center. You seem to agree with that. You agree that that acceleration is going to require a force? (your words "the walls need to exert a force to speed it up" but before that you say there is "no force".) I was showing how much force will be required to stop it on its outward path. It will take a force as large as its required centripetal force (calculable using mv^2/r) to make it attain a circular motion. I reiterate, you need to learn Newton's laws of motion before you do anything else involving mechanics. Without that, you can't possibly understand what's going on. On day one of introductory physics you would be introduced to the concept of vectors. Forces are vectors, which means they have components which are perpendicular to each other. A force in one direction has no effect on motion in the perpendicular direction. Thus, a tangential force has no effect on the radial motion. Put another way, using a concept from later on in the first semester of physics, a tangential force does no work in the radial direction. I thought you understood these basic concepts, so when I was talking about tangential acceleration I was not talking about the radial direction. Obviously, I was wrong. I tested that ratio to the tangential speed many times in an Excel spreadsheet, and I graphed radius to the centripetal force. As the radius increases the required centripetal force increases linearly too. Friction between the wall and the mass is constant. So the ratio of Fc:Friction is not constant. Speed is proportional to radius at a constant omega (w). That part is definitely right. Today I hope to observe the angle the mass exits the tube by experiment. Is it tangentially (Swansont) or at an angle to the tangent as I suspect? Go ahead and do the physics. Take a physics class if necessary. I'm tired of going over the same ground. 18 freaking pages, and we're stuck on misunderstanding of vector components and how to apply Newton's laws of motion. 1
Robittybob1 Posted May 17, 2015 Posted May 17, 2015 (edited) "What pushes you?" : Nothing. There is no force "pushing" you. "What force overcame the force of friction?" : Your inertia. As the merry-go-round spins, your inertia means your body wants to keep going in a straight line. The friction with the surface allows a centripetal acceleration to be applied, that keeps you going in the circle. As it speeds up, it's harder to keep you going in that circle. The force of the friction is not enough and you start to slide (outwards, it seems, but essentially trying harder and harder to go in a straight line). The centripetal force is no longer enough to counter the inertia. It's the same answer. Again and again. Didn't Swansont say inertia is not a force? I have heard of people talking about inertial forces but I wasn't sure if that is right though. So these inertial forces need to be opposite direction to the centripetal forces then. Which is possible for the difference between going in a straight line and going in a circle is a change in direction - inward toward the center. I reiterate, you need to learn Newton's laws of motion before you do anything else involving mechanics. Without that, you can't possibly understand what's going on. On day one of introductory physics you would be introduced to the concept of vectors. Forces are vectors, which means they have components which are perpendicular to each other. I thought you understood these basic concepts, so when I was talking about tangential acceleration I was not talking about the radial direction. Obviously, I was wrong. Go ahead and do the physics. Take a physics class if necessary. I'm tired of going over the same ground. 18 freaking pages, and we're stuck on misunderstanding of vector components and how to apply Newton's laws of motion. I did the experiment and the motion was not strictly tangential. So I would say there are other factors involved that you don't know about. Thus, a tangential force has no effect on the radial motion. Put another way, using a concept from later on in the first semester of physics, a tangential force does no work in the radial direction. Can you give me an example? Are you thinking of a pulley with a belt running around it? As to whether a force does work that would depend on the change of distance. A static centripetal force doesn't do work as far as I know but there would be work done slipping against friction (and that was a centripetal force.) A force in one direction has no effect on motion in the perpendicular direction. Yet it is the centripetal force that makes an object moving in a tangential direction travel in a circle! Edited May 17, 2015 by Robittybob1 -1
Robittybob1 Posted May 17, 2015 Posted May 17, 2015 Looks like I'll have to try and run the experiment again in a way I can take accurate measurements and see if I can explain it with maths. This is a bit tricky as I don't have laboratory equipment that I'll need. Are there any students out there?
Mike Smith Cosmos Posted May 17, 2015 Author Posted May 17, 2015 (edited) . . I think it would be fair to say that the root of all this dilemma about is INERTIA . link to Wikipedia on inertia and the of property of matter , mass and it's movement or reluctance to move Link :- http://en.m.wikipedia.org/wiki/Inertia -------------------------------------------------- Isaac Newton in his Principea said :- " The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line." ---------------------------------------------------- So the root driver in this whole " centrifugal force " scenario appears to be the particular MASS or object that is being considered for this experiment, phenomenon , observation , or analysis. So if we look closely at the particular mass involved we may gain a clearer picture of what is happening in the 'world ' of that MASS . It could be the mass is something , loosely gripped in a tube, a person on a merry go round, a brick on the end of a string , or water in a bucket ( which itself) is being held by string . The main consideration is the MASS ( person, water, brick ,lead & cloth lizard ) it's inertia . What does it want to stubbornly do ? Where does it go, ? What forces act on it if any ? Who wins, where and how does it go ? And what sort of going ? ( stay still, move with a velocity, accelerate? ) And in fact is there any " fleeing from the centre " CENTRIFUGAL ACTIVITY going on ? If there is we need to identify , is it real, is it fictitious, etc etc whatever, as it does have answers to the OP. And Gravity. Mike Edited May 17, 2015 by Mike Smith Cosmos
imatfaal Posted May 17, 2015 Posted May 17, 2015 I think it would be fair to say that the root of all this dilemma is INERTIA .... I am afraid the root of the problem is culpable ignorance and a refusal to understand. This is PHYSICS - it would be great if Mike and Rob would stop hand-waving and start considering some first year science. I learnt this stuff when I was 11 - before I had even elected to take physics O'Level; it is very very basic. 1. Observations can be confusing. You don't just guess what the explanation is, you don't look at a moving object and estimate it's direction and speed, and you don't assume that your explanation is backed up by the facts. 2 . When you fail to understand you simplify. Stop talking about motorbikes and crash barriers, stuffed lizards, and pet dogs. Don't bring in concepts that you don't understand such as the conservation of angular momentum when you are clearly crashing and burning at the level of the first law. 3. If your simple thought-experiment threatens to overturn 400 years of the observations and the conclusions of people of the calibre of Galileo and Newton then take a short break, make a quick self check for signs of hubris, and conclude that you may need to re-examine your foundational knowledge. For crying out loud - this is a science forum and those claiming to have new different knowledge that overturns the most basic tenet of physics have gone 18 pages without showing one piece of experimental evidence! All you need is a conker on a string and a smart phone 3
Mike Smith Cosmos Posted May 17, 2015 Author Posted May 17, 2015 (edited) For crying out loud - this is a science forum and those claiming to have new different knowledge that overturns the most basic tenet of physics have gone 18 pages without showing one piece of experimental evidence! All you need is a conker on a string and a smart phone I have it on my I pad , my daughter says I need to register for you tube. Which I will try to do today if I can ( unfortunately I am an old hand , and am not up with all the modern gadgetry . I have tried to upload directly , it won't work . ) Mike -------------------------------------- -------- Speculative . - HUNCH My hunch is , which I must say is at the early stages , in the cases , or many of the cases I , and others have been proposing , like cloth and lead lizards in cardboard carpet tubes, other tubes, motorbikes around corners, water in buckets, people on kiddies roundabouts , that :- The founders of:- Typical quote . " there is no such thing as Centrifugal force , only centripetal is a real force , centrifugal is a reaction, fictitious, " I suggest that they have screwed up , and got it the wrong way round ! The originating device is not the ' pushing in 'centripetal force ( that is the reaction, the fictitious force, in many of these examples) The real source , driver of these , above mentioned examples is the mass-inertia in its clear ,natural, Newtonian stubbornness to continue in a straight line. Provided by whatever means to get this inertia, ( by moving tubes , rotating roundabouts, swinging weights and water. These things have been given from somewhere the ' STRAIGHT LINE INERTIA ' . When confronted with change , in these applications, the 'straight line inertia ', starts the ball rolling by generating a centrifugal force, when they come up against resistance to their straight line Inertia. This then , I am proposing ( possibly heretically ) , invokes a reaction fictitious force the centripetal force . The two sometimes, and sometimes not balance. When they balance on a radius. There is no ACTUAL ACCELERATION down the radius towards the center. The mass prescribes a circle with no net acceleration along ( in or out , on the radius ) . A straight circle ( no change in radius) . In the event of a winning scenario for the centrifugal force , the mass moves to a higher orbit. If it leaves totally , the constraint of the circulating device, it then goes its way with a mixture of tangential velocity and an additional input from whatever content of momentum (m x v), it may have picked up in its outward travel along the radius. Just a Speculative Hunch. , at this stage. You will probably say this is Audacious . However I feel moved to say how I 'hunch' . Evidence on 'you tube ' link to follow shortly , once I have uploaded it to You tube . Mike Edited May 17, 2015 by Mike Smith Cosmos -1
imatfaal Posted May 17, 2015 Posted May 17, 2015 You are not using force nor acceleration in the manner that scientists do. If you with to recreate concepts and name things as you wish then anything can be claimed to be correct. "When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean—neither more nor less." Humpty Dumpty and Alice. From Through the Looking-Glass. Illustration by John Tenniel. 1
swansont Posted May 17, 2015 Posted May 17, 2015 Speculative . - HUNCH My hunch is , which I must say is at the early stages , in the cases , or many of the cases I , and others have been proposing , like cloth and lead lizards in cardboard carpet tubes, other tubes, motorbikes around corners, water in buckets, people on kiddies roundabouts , that :- The founders of:- Typical quote . " there is no such thing as Centrifugal force , only centripetal is a real force , centrifugal is a reaction, fictitious, " I suggest that they have screwed up , and got it the wrong way round ! Your hunch is wrong. If you had bothered to follow any of the discussion in this and related threads, you would see why. ——————————————— I had a conversation at work the other day. A colleague had been trying to figure out why two devices were giving the same signal, when there was an effect that should make them different. I realized there was a second difference between the two, and the effects should cancel. He paused, and said, "Oh yeah. I hadn't thought about that." He was happy. He learned something. (many times the roles have been reversed in this kind of conversation). He went and told someone else why it's OK the signals were the same. It was refreshing. Because he didn't ignore my correct observation. He didn't double down on his insistence that the signals should be different. He didn't posit a hunch that all of the science was wrong. He didn't ignore the math. He didn't try and come up with a more convoluted scenario, or redefine the terminology, to try and sneak some way he could be considered right into it. He didn't leap ahead into an even more advanced area of science, without having understood more basic phenomena. It was refreshing, but not surprising, because it was science and not crackpottery. Such discussions are one of many reasons I've enjoyed working in science, both in research and teaching. [/morality play] 2
Robittybob1 Posted May 17, 2015 Posted May 17, 2015 (edited) Looks like I'll have to try and run the experiment again in a way I can take accurate measurements and see if I can explain it with maths. This is a bit tricky as I don't have laboratory equipment that I'll need. Are there any students out there? As I dosed off last night I thought spinning a friction free air track could be the way to go for then the rate of rotation would be much slower and hence easier to time. If one of those was mount horizontally but radially to a circle and the spun it slowly in a circle. Would the glider move along the track? Measure its speed at the time it hits the end of the track. Do a vector analysis of the two speeds tangential and radial. Estimate its path if it left the system. I have it on my I pad , my daughter says I need to register for you tube. Which I will try to do today if I can ( unfortunately I am an old hand , and am not up with all the modern gadgetry . I have tried to upload directly , it won't work . ) Mike .... Just a Speculative Hunch. , at this stage. You will probably say this is Audacious . However I feel moved to say how I 'hunch' . Evidence on 'you tube ' link to follow shortly , once I have uploaded it to You tube . Mike Can't wait to see this. Edited May 17, 2015 by Robittybob1
Klaynos Posted May 17, 2015 Posted May 17, 2015 http://iopscience.iop.org/0031-9120/18/5/312/pdf/pev18i5p234.pdf I used to teach this experiment. If you modify it a bit you can show that roulette is predictable and measure the corollas effect. The physics is well understood and tested. There are a few people who seem resilient to learning the physics required. I don't think we can realy help that. Yes I've followed the whole thread and cannot believe frustration hasn't shown earlier. 1
Robittybob1 Posted May 17, 2015 Posted May 17, 2015 http://iopscience.iop.org/0031-9120/18/5/312/pdf/pev18i5p234.pdf I used to teach this experiment. If you modify it a bit you can show that roulette is predictable and measure the corollas effect. The physics is well understood and tested. There are a few people who seem resilient to learning the physics required. I don't think we can realy help that. Yes I've followed the whole thread and cannot believe frustration hasn't shown earlier. Couldn't read the link without paying! Frustration! I hope you taught them how to spell as well "Coriolis".
Robittybob1 Posted May 17, 2015 Posted May 17, 2015 Google the title? It covers the maths nicely. Thanks from http://isites.harvard.edu/fs/docs/icb.topic1216311.files/Project%20resources/Rolling%20sphere%20on%20turntable/turntablemodel.pdf ω = angular velocity of rotating turntable Ω = angular velocity of rolling sphere and in the end Ω = 2/7ω That is nowhere enough compared to the results I was getting yesterday, so the two situations are a bit different.
physica Posted May 17, 2015 Posted May 17, 2015 The physics is well understood and tested. There are a few people who seem resilient to learning the physics required. I don't think we can realy help that. Yes I've followed the whole thread and cannot believe frustration hasn't shown earlier. After seeing the reply to my first post I didn't think the effort was worth it as it would fall on deaf ears. My hypothesis was right. Some of the people on this thread deserve a medal.
xyzt Posted May 17, 2015 Posted May 17, 2015 (edited) Your hunch is wrong. If you had bothered to follow any of the discussion in this and related threads, you would see why. ——————————————— I had a conversation at work the other day. A colleague had been trying to figure out why two devices were giving the same signal, when there was an effect that should make them different. I realized there was a second difference between the two, and the effects should cancel. He paused, and said, "Oh yeah. I hadn't thought about that." He was happy. He learned something. (many times the roles have been reversed in this kind of conversation). He went and told someone else why it's OK the signals were the same. It was refreshing. Because he didn't ignore my correct observation. He didn't double down on his insistence that the signals should be different. He didn't posit a hunch that all of the science was wrong. He didn't ignore the math. He didn't try and come up with a more convoluted scenario, or redefine the terminology, to try and sneak some way he could be considered right into it. He didn't leap ahead into an even more advanced area of science, without having understood more basic phenomena. It was refreshing, but not surprising, because it was science and not crackpottery. Such discussions are one of many reasons I've enjoyed working in science, both in research and teaching. [/morality play] It does happen (in real life, with real scientifically minded people). Not very often in this forum where trolling and time wasting is "du rigueur". Where is the fun in accepting a rational, scientific, rigorous explanation when you could stretch the thread on 10 more pages? Edited May 17, 2015 by xyzt
studiot Posted May 17, 2015 Posted May 17, 2015 Mike may have been a victim of the engineering education system 30 to 50 years ago when they were teaching this stuff. But no one has commented on my post#329 where they are still teaching it today.
tar Posted May 18, 2015 Posted May 18, 2015 SwansonT, I may have misread your account of your refreshing conversation with someone working on a problem where you pointed out an angle he was not taking into consideration, when the results did not match with what the "effect" predicted, but it sounded a little like you thought a little out of the box, he/she was confined to. You did not suggest physics was wrong, you just pointed out another way to look at, that would explain what was going on. You were not adding a complication, you were noticing a contributing factor to the results. RobbityBob1, By the pictures of the centrfugal pump you showed, it looked like the propellers/impellers were directing the fluid in a direction tangent to the outside circumference of the pump, and the only outlet for the pressure going out in all the tangential directions was one particular tangential path. It was not a radial outlet. The only thing that made it centrifugal, or center fleeing is that the inlet was near the center and the fluid was pushed outward by the fins, winding up leaving the circle by a tangential path. Regards, TAR Studiot, You make an interesting point. I took my highschool physics in the late 70s. They might have taught me something that is no longer taught, because it conflicts with some results or another. Interesting to me, because engineers and physicists had no problem building things and using things that went around in circles, when I was young. Their ideas were probably not ignorant speculations, at the time. Regards, TAR So what are the odds that motion was completely understood 400 years ago, misunderstood 50 years ago, and understood perfectly again just recently? I know I am being silly, but just making the point, that you cannot tell me SwansonT understands Newton's laws, and my Physics teacher at NJIT in the 80s had no clue. Well I suppose you can tell me I didn't understand what my teacher was saying...but that's a different point. One of the videos linked in this thread, started by stating we don't know what inertia is, just that bodies have a tendency, or a desire, to keep going in a straight line. I think its OK to speculate on what inertia is. None here would say a force is required to keep a body going in a straight line. But there is a definite argument that a force was required to disturb the resting mass, and get it going in the first place. Being that inertia is the same over time, if you exert a force on a resting object, to accelerate it to a constant speed, in a sense, that force has been embodied by the mass. I would imagine there would be quite an effect resulting from the Earth slamming into a stationary wall. The force the Earth would apply to the wall would come from its inertia, in a sense. Regards, TAR
Robittybob1 Posted May 18, 2015 Posted May 18, 2015 (edited) RobbityBob1, By the pictures of the centrfugal pump you showed, it looked like the propellers/impellers were directing the fluid in a direction tangent to the outside circumference of the pump, and the only outlet for the pressure going out in all the tangential directions was one particular tangential path. It was not a radial outlet. The only thing that made it centrifugal, or center fleeing is that the inlet was near the center and the fluid was pushed outward by the fins, winding up leaving the circle by a tangential path. Regards, TAR Centrifugal pumps would be designed to maximize the pressure and the throughput. I have seen their shape and they are definitely designed to thrust the liquids outward, drawing new liquid into the central inlet. Now in the design of my juice extractor using centrifugal force I reversed the rotation of a normal centrifugal pump, and the engineers who were working with me took a bet with me for they thought that if the direction of rotation of a centrifugal pump was reversed it would reverse the direction of the fluid going through it, but they were wrong. OK it wasn't as efficient but it pumps regardless of the spin direction of the rotor. In the experiment I tried to keep the tube continually radial so not to accentuated the "pumping action". OK I wasn't working with a fluid but a solid mass. Today I followed up with some lessons on Newton's Second Law of motion and there were examples that motion vectors were added. If the liquid is rushing along the vanes to the outer edge, that motion has to be added to the tangential motion and together you get an exit direction that is predominantly tangential but not perfectly tangential. The question still stands as to what "pushes" the fluid through a centrifugal pump, but the fact is that it does. It takes a lot of energy to achieve the effect. Once the fluid is given extra energy, its angular momentum forbids the fluid moving inward, only allowing an outward motion. The same is happening with a solid object because the centripetal force is the friction and back pressure so as long as there is somewhere for the liquid to go the object's inertia that friction is soon exceeded. Edited May 18, 2015 by Robittybob1
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