RenegadeOfPhunk Posted September 21, 2004 Share Posted September 21, 2004 The following is a discussion of this statement: Alright, why centrifugal force isn't actually real. Centrifugal force is the notion that when you are on a spinning object there is some force that is trying to throw you outwards off of it. Like when you're traveling in a car and it makes a sharp rightwards turn you feel like you're being thrown to the left. this is simply a misconception of what is really happening, in that you are not being thrown any direction, your body is actually just trying to continue in the straight line it was headed in before the car abruptly turned. The CAR is actually applying a rightwards force on you, which is what keeps you inside and going the same direction as the car itself, but most people misconceive of this as YOU pushing out against the car. Centripetal force is the force of the car holding you inside and keeping your body moving in a circular path instead of flying straight like it wants too. This conversation came originally from this thread: http://www.lucasforums.com/showthread.php?s=&postid=1637275#post1637275 I've created this new thread so as to not de-rail the original. ...anyway - what you seem to be missing here ET, is a basic law of physics: 'For every action, there is an equal and opposite re-action'. ...it doesn't say 'For every action, there is an equal and opposite 'imaginary' re-action!'. The reaction of centrifugal force to centripital force is just as real as any other force - I assure you. The fact that it happens to be a 're-actionary' force is just a detail. In your example, the force applied by the car on the person is the centripital force. The person's body is not able to take the course it naturally wants to take because the car is forcing against that person - to deviate their course... ...however if the locking mechanism on the door were to break, or the window smash due to the 'force' of the body pressing against it, it would NOT be centripital forces causing the door to break (centripital forces are only acting on the person in the car -NOT the car itself..) - it would be the centrifugal force acting in opposition to the centripital force. (i.e. the person forcing against the car door to try and keep moving in a straight line..) ...and I know of NO 'imaginary' forces which can break door mechanisms... I assure you, both forces are as real as each-other. Just because a force is a result of a re-action, doens't mean it's imaginary! ..if this were really the case, rockets would have no 'real' forward thrust (only imaginary), since the forward thrust of a rocket is a 're-action' to the force of the combusted fuel being ejected in the opposite direction... (or the forward thrust of the rocket is real and the backwards thrust of the combusted fuel is imaginary - if you so choose. Doesn't matter - either way is incorrect, because neither force is 'imaginary') Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 21, 2004 Author Share Posted September 21, 2004 iamtrip makes a better point than he realises If you want to find 'imaginary' forces, you'll have to look to the Star Wars films, cos you'll find none in reality Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 21, 2004 Author Share Posted September 21, 2004 To cover some other points you made in the other thread: That website was wrong about centrifugal force being the third law counter to centripetal force, No - actually the website (http://www.infoplease.com/ce6/sci/A0811114.html) got it spot on. This isn't some quack webiste, it's a perfectly legitimate source of information... in the case of someone OUTSIDE of the earth it is gravity that is countering centripetal force, nothing else. No - not really accurate. When considering the Earth and everything attracted to it because of it's gravitation (including us), the centripital force IS the Earth's gravity, combined with it's rotation. i.e. we feel the effects of this centripital force. The counter-force (the perfectly real centrifugal force) is felt by the Earth itself, causing it to 'wobble' slightly. Of course any wobble on the Earth caused by our little insignificant selves is not worth mentioning. ...the centrifugal effects of the moon as it rotates in Earth's orbit - however - causes a far more noticible 'wobble' on the Earth... This same principle can be seen when considering the Sun and all the planets which orbit it. The planets are kept in orbit by the centripital force of the Sun's gravity. In reaction to this, a centrifugal force acts on the Sun, causing it to 'wobble' back and forth... ...I'm hoping this example helps you understand that both the centripital and centrifugal forces are both legitamate, 'real' forces. One is acting on a planet (keeping it in orbit), and the other is causing a massive star to wobble back and forth several million miles away! In the case of a car it's a normal force of you pushing back against the car door, not centrifugal force. The truth is actually the exact opposite of what you just said... ...[the] force of you pushing back against the car door, IS a centrifugal force. (You know, the one you don't believe is really happenning...) Any force acting on the person by the car is the centripital force (created by the car.) ...but any force acting by the person on the car is the centrifugal force (created 'by the person' as a result of that persons momentum..) Link to comment Share on other sites More sharing options...
Spider AL Posted September 21, 2004 Share Posted September 21, 2004 While Renegade is slightly correct in pointing out that centrifugal and centripetal "forces" are terms used to describe the behavior of say... the water in a bucket that's being spun around, and the bucket itself,.. I have to agree with ET, in that calling them "forces" is redundant, since the force keeping the water in the bucket is in fact inertial force. Even physicists agree upon this point, saying that centripetal force is the counter-force to the INERTIAL force operating on the water in the bucket, not "centrifugal FORCE", which they call a "pseudo-force". And though physicists claim that the act of gripping the bucket and preventing it and the water from flying away is in some way exerting "centripetal force" upon the object, I think this too is redundant, as other forces account for this. And also that the force keeping the water from breaking the bucket and flying free isn't "centripetal force" but is in fact the molecular integrity of the material which the bucket is made of and the molecular forces thereof. One must remember that these terms were invented and bandied about quite a long time ago. They should be updated to conform more closely with international standard physics terminology IMO. As such I consider centrifugal "force" to be obsolete as a term. Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 21, 2004 Author Share Posted September 21, 2004 Well - after looking more into the concept of 'pseudo' forces, I must admit I do have a bit of egg on my face, since I didn't even think such a term existed. So unreserved apologies to you ET. I was certainly wrong to think that the idea of 'imaginary' forces wasn't an established one. I was definalty wrong there... ...however, the more I look into it, the more I think nothing is really settled on this issue - as you have already eluded to Spider. For example, take a look here: http://www.physicsnews1.com/question_5.html Now - while I'm fairly sure this is reasonably recent, of course I can't give you the immediate credibility of the writer. That would take some investigating. ...but what he's saying is exactly what I've been saying. And I still don't see why I'm wrong - even though there is obviously a fair amount of educated opinion which disagrees with me... ...why aren't the acting and re-acting forces involved in circular motion treated in the same manner as other acting / re-acting forces - like the rocket example I gave earlier... ...or did I get it wrong about the rocket - are one of those forces (the fuel being pushed out the back and the rocket itself being pushed the other way) ... viewed as 'imaginary'?! ... if so, why? To me (and maybe this is the old-school thinking being mentioned in that link...) a force is something which causes a quantifiable effect. Whether it's to do with something active or something re-active, or whether it's because of the existience of something or the lack of something is just a detail of what causes that force. ...and to me, centrifugal and centripital forces come under the classic heading of 'opposing forces'. To me, this renaming of things in modern physics doesn't represent a new level of understanding at all. It's just a renaming excerise- specifically of what the word 'force' means... For instance, Spider - you said that instead of using the term centrifugal force (which apparently is pseudo in nature..), you should more correctly say INERTIAL force. ...so is this INERTAL force you speak of imaginary too? Or is it real? If it's still imaginary, you seem to have just swapped the term 'centrifugal' for 'inertial'. And since I already knew that centrifugal forces (as I think of them) are caused by inertia, that name tells me nothing new... However, if this is a 'real' force, then I guess you need to explain to me why changing the name has suddenly made it 'real'? In short, I'm dubious as to whether this change is actually triggered by (or actually allows) a more fundemental understanding of physics. I suspect this may be more about - as you've hinted towards - merely an exercise in standardisation concerning the word 'force'... So while I will admit I seem to be a little behind the times, I would like to at least have it recognised that - as far as I'm aware - going by the 'classic' definition of a force, everything I've written thus far is absolutely correct. ...and I think any calculations I ended up peforming would come out just as correct as any performed using 'imaginary' forces.. But I suppose that's like my Dad telling me he could count his money just as well when he used shillings and farthings ...man - now I feel old :/ Link to comment Share on other sites More sharing options...
ET Warrior Posted September 21, 2004 Share Posted September 21, 2004 The issue here is that centrifugal force is trying to describe the feeling of you being thrown OUTwards from a rotating object, when in effect you are truly only feeling the effects of the centripetal acceleration.. I shall demonstrate witha diagram. In this picture imagine that we have a person standing on Earth's surface at point A. The arrow up represents the force of the centripetal acceleration acting on the man due to the rotation of the earth. The down arrow is the force of the earths gravity. Now, technically these are not force pairs, because a newtons force pair is denoted as force of B on A is equal and opposite to the force of A on B. In our case, there are a lot more forces at work in this picture than I have drawn. For example, the force pair to gravity holding me down is my gravity pulling the earth up (from my perspective) The pair to the centripetal acceleration on me from the earths rotation is the centripetal acceleration on the earth by ME. Nowhere in these forces is centrifugal force needed. Now if you wanted to call one of the forces centrifugal force you COULD, though it would be incorrect, because we already have names for the other forces acting on objects. And it's not really a renaming of physics notions as you imply in your post, but an updated sense of understanding exactly what is occuring between objects, and therefore using new terminology that is more significant and descriptive of what is really going on. Furthermore, your description of the forces in the solar system are incorrect in that it is gravity and electrical forces that hold the planets to the sun, it is the centripetal force of their rotation that keeps them AWAY from the sun as well. Edit - the equation for determining Centripetal acceleration is (mass*velocity^2)/radius This makes sense, because the faster you swing something in a circle the more it feels like it wants to pull away from you. Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 21, 2004 Author Share Posted September 21, 2004 Yes -I think I'm getting what your saying ET. ...all the forces I know of and understand are present in your explinations. And while it does seem to be a renaming exersise, I think I'm understanding why these naming changes are probably helpful. ...ok - looks like I'm going back to school Thx for this heads up. And forgive an old fool like me for not keeping up with the times Link to comment Share on other sites More sharing options...
Spider AL Posted September 21, 2004 Share Posted September 21, 2004 RenegadeOfPhunk: ...and to me, centrifugal and centripital forces come under the classic heading of 'opposing forces'. To me, this renaming of things in modern physics doesn't represent a new level of understanding at all. It's just a renaming excerise- specifically of what the word 'force' means... For instance, Spider - you said that instead of using the term centrifugal force (which apparently is pseudo in nature..), you should more correctly say INERTIAL force. ...so is this INERTAL force you speak of imaginary too? Or is it real? If it's still imaginary, you seem to have just swapped the term 'centrifugal' for 'inertial'. And since I already knew that centrifugal forces (as I think of them) are caused by inertia, that name tells me nothing new... However, if this is a 'real' force, then I guess you need to explain to me why changing the name has suddenly made it 'real'? In short, I'm dubious as to whether this change is actually triggered by (or actually allows) a more fundemental understanding of physics. I suspect this may be more about - as you've hinted towards - merely an exercise in standardisation concerning the word 'force'... You ask a valid question, and I agree IN THAT I don't think that it matters what we call the force that keeps the water in the bucket... I mean, you could call it banana force for all the difference it would make... But A: standardising scientific terms is one of the most important things in science since all scientists have to sing from the same hymn-sheets. And of course, B: Inertia is a basic force. Calling the effects of angular momentum "centrifugal force" is like calling sea-salt "an element". Salt's made up of two basic building blocks, sodium and chlorine. Likewise the behaviour of the water in the bucket is made up of several basic physical building blocks, that are termed "forces". Such as inertia. So the update is all good! Well - after looking more into the concept of 'pseudo' forces, I must admit I do have a bit of egg on my face, since I didn't even think such a term existed. So unreserved apologies to you ET. I was certainly wrong to think that the idea of 'imaginary' forces wasn't an established one. I was definalty wrong there... It takes a big man to say stuff like this, especially on an anonymous internet forum. You certainly have MY respect for doing so. Link to comment Share on other sites More sharing options...
ET Warrior Posted September 21, 2004 Share Posted September 21, 2004 Originally posted by Spider AL It takes a big man to say stuff like this, especially on an anonymous internet forum. You certainly have MY respect for doing so. Deffinately, It's a nice refresh after debating against people who refuse to acknowledge that they may be incorrect, even if it's mostly just an issue of semantics (as in our case it seems) I will appologize a bit for some of the fervor I brought into my arguments, but I have recently contemplated changing majors into physics, so I'm very outspoken on the subject Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 21, 2004 Author Share Posted September 21, 2004 It takes a big man to say stuff like this, especially on an anonymous internet forum. You certainly have MY respect for doing so. Heh -I've seen too many truly hideous examples of people who knowing full well they've got it wrong trying anything they can to squirm out of earlier statements... ...best to just bite the bullet and get on with it... Well -now that (I hope) were all friends again, maybe one of you can explain a bit more about how this new way of thinking affects Newton's third law? (I'm wondering if it still has any relevance ) ...from the way you were talking earlier ET, it seemed that you let the opposing forces implied by the third law effectively cancel each-other out in your calculations - in a way that means you can effectively discard them?! ...is that in any way accurate? ..if this is accurate - doesn't this mean that you've effectively negated the need for the third law at all?!! Specifically, I mean when you said this... Now, technically these are not force pairs, because a newtons force pair is denoted as force of B on A is equal and opposite to the force of A on B. I will appologize a bit for some of the fervor I brought into my arguments No need to apologise. If anybody was acting like a twat, it was me to be honest... [edit] So what is your name for the force which causes the Sun to 'wobble' as the planets orbit it..? ...ahh hang on - think you've already explained it. The wobble on the Sun is simply caused by ... the gravitational force of the planets themselves .... right? ....hmmm - well, as annoyed as I am that I have to relearn a whole load of crap, I must admit that does seem a far simpler way of looking at it...! But I'm still wondering where Newton's third law comes into play here...if at all... [/edit] Link to comment Share on other sites More sharing options...
ET Warrior Posted September 21, 2004 Share Posted September 21, 2004 It's not that they cancel each other atall, it's just that the FORCE between them is equal. I am currently exerting the exact same amount of gravitational force on the Earth as the earth is exerting on me. A bizarre concept, but quite true. The reason I am so affected is because of our masses. The force has a more pronounced effect on me and my small mass, while the earth's huge mass is relatively unaffected. You cannot discard them because the forces they are applying are very real, it's just that they are in effect completely equal and opposite. Just as in a car accident between a Cooper Mini and a Mack truck, both vehicles exert the same amount of force on each other, but the mini gets destroyed because it's small mass is accelerated much more quickly than that of the truck. Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 22, 2004 Author Share Posted September 22, 2004 I am currently exerting the exact same amount of gravitational force on the Earth as the earth is exerting on me. A bizarre concept, but quite true. The reason I am so affected is because of our masses. The force has a more pronounced effect on me and my small mass, while the earth's huge mass is relatively unaffected. Yes - this is all suddenly clicking together for me. And I'm finally understanding why your correct in saying that this is more than just a simple renaming exersise. I mean, I did already understand what you've just said above - in practical terms. I hope this should be obvious from what I posted in my first post. But the problem is that not only did I have the names of the forces wrong, I also think I had the forces pointing in the wrong directions... Like you were trying to explain to me earlier - you dont' think of the centripital force as pointing inwards to the centre of the circular movement anymore. The force now points (more logically I must admit) in the direction of the circular movement itself (i.e. at a right-angle to the way I used to think of it). And this now solves my temporary distress about what i saw as Newton's third law being scrapped! I only thought the counter-forces had disappeared because I still had my forces (stubbonly ) fixed in the wrong directions.. Ok - so I must say I'm converted. This new way of approaching forces is just plain a better way to approach things... ...I guess I only have one final question - a pedantic one perhaps, but I'll ask it anyway... Why is centripital force (or I guess the term you were using was centripital 'acceleration' earlier) still called 'centripital' anything, since the force (or the acceleration caused by the force -whatever) is not strictly 'centre-seeking' anymore - as far as I can see... ..it's now at a right-angle to 'centre-seeking'. Is this just carrying a familiar term forward to help us fuddy-duddy's adjust or something? ...if so, let me suggest that it's (well, I was gonna say 'wrong', but I'll say 'unfortunate' instead...) to use the same term for a force that has now 'apparently' changed it's direction at a right-angle from where it used to point...! Or is this another case where I'm not quite understanding the new terms...? Link to comment Share on other sites More sharing options...
ET Warrior Posted September 22, 2004 Share Posted September 22, 2004 You're still a little off on Centripetal acceleration, it is not perpendicular to your old perception of it pointing inwards. Centripetal acceleration is outwards. Were the earth to start spinning much faster, eventually our centripetal acceleration would be approximately 9.8 m/s/s and would be a complete counter to gravity, meaning that we would experience weightlessness on earth, because we'd have two forces of equal magnitude pointing in opposite directions, and they would therefore cancel meaning we would experience no NET force. Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 22, 2004 Author Share Posted September 22, 2004 Centripetal acceleration is outwards. Why is the word 'centripital' - meaning centre-seeking - used to describe a force acting in a totally opposite direction?! (i.e. 'outwards' from the centre?!) Were the earth to start spinning much faster, eventually our centripetal acceleration would be approximately 9.8 m/s/s and would be a complete counter to gravity, meaning that we would experience weightlessness on earth, because we'd have two forces of equal magnitude pointing in opposite directions, and they would therefore cancel meaning we would experience no NET force. I'm not trying to be confruntational here - honestly I am not. But your telling me something I already knew... I would have worked out what you just said just fine with my old 'understanding' of centripital and centrifugal forces. You would have said the terms are wrong, and the centrifugal force was 'imaginary', but I would have come to the same conclusion... So please -you don't need to keep explaining the fact that forces can completly cancel each-other out and what-not. I totally understand and comprehend this... This is just a matter of understanding the new 'lingo', and the new way of looking at things. Now that we've covered the 'Earth and us' example, maybe we can cover one of your previous statements in the other thead: Centripetal force is the force of the car holding you inside and keeping your body moving in a circular path instead of flying straight like it wants too. Could you do a couple of things for me... a. Draw a quick diagram showing exactly what direction this centripital force is acting in this case and b. Describe the counter-force to this centripital force (required to fulfill Newton's third law) and what effects this 'counter' force is having in this senario... Hopefully this will clear up what I'm missing here... Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 22, 2004 Author Share Posted September 22, 2004 As I look more and more into various explinations from various sources about why centrifugal force is 'imaginary', I notice a reccuring theme... They always talk about a very specific type of senario where - for example - a person is travelling in a car and that car changes from a straight path to a curved path. ...they usually say something like this: 'Many people are under the misconception that when someone ends up sliding across the car seat' as the car turns the corner, that this movement is caused by 'centrifugal force'. This is in fact not true. The person sliding may seem to feel like there is a force 'pushing' them towards the side of the car, but this is in fact a force only in their perception. Or in other words, it is an 'imaginary' force. The truth - in fact - is that the person is sliding across that car seat not because a force is causing that movement, but because their existing inertia - built up by the force of the car seat on their body while the car was travelling in a straight line - is now causing that body to continue moving in that original straight line. ...you can see this more clearly if you consider that it is actually the car itself that is changing course. And so rather than the person sliding along the car seat, it is actually the car itself that is changing course 'under' the person, while the person continues to move in a straight line due to their inertia..' Well fine. I've got no problem with that. And you wanna know why? Because I already knew that before you said anything to me...! ...you don't beleive me? Heh - perhaps you think I'm trying to do exactly what I said I wouldn't do - i.e. try and squirm my way out of earlier statements...? I really am not. I already completely understood that when someone slides along a car seat when it turns, it is not a force which causes that - centrifugal or otherwise. ...to confirm I'm telling the truth, look back on my previous posts and find any instance where I stated this. i.e. that when someone slides around in a turning car, that's to do with centrifugal forces... ...you won't find any, cos I never said it. ...what I DID talk about, however, was the situation after that person had finished sliding and was in contact with the door - and where the centripital force which starts moving them along with the car starts kicking in. ...only at THIS point was I arguing that centripital and centrifugal forces come into play. And the more I think about it, the more I can't grasp why it is that what I said in the first post of this thread - (thinking specifically about the body in the car senario here) was in fact wrong. I'm sorry if you think I'm wasting your time here, but I would appreciate it if you could again consider what I said in that first post... In your example, the force applied by the car on the person is the centripital force. The person's body is not able to take the course it naturally wants to take because the car is forcing against that person - to deviate their course... ...however if the locking mechanism on the door were to break, or the window smash due to the 'force' of the body pressing against it, it would NOT be centripital forces causing the door to break (centripital forces are only acting on the person in the car -NOT the car itself..) - it would be the centrifugal force acting in opposition to the centripital force. (i.e. the person forcing against the car door to try and keep moving in a straight line..) ...and I know of NO 'imaginary' forces which can break door mechanisms... First of all, just to make it clear once more that I'm not talking about the body sliding around on the car seat.. ...I am talking about the body being forced into a curved path by the car door. Secondly, I want to (hopefully) confirm that the force of the door against that person is called the 'centripital force' (centre-seeking force). ANd thirdly, I want to confirm that there is an equal and opposite force acting counter to the centripital force. We both knew it was there, cos we both said so. Here is what you said in the other thread: In the case of a car it's a normal force of you pushing back against the car door, not centrifugal force. Here is what I said concerning that same force: it would be the centrifugal force acting in opposition to the centripital force. (i.e. the person forcing against the car door to try and keep moving in a straight line..) You know what, we are both talking about exactly the same bloody force. And we both knew that it was a real, non-fictional, non-imaginary force. The fact I happenned to call it a 'centrifugal force' is but a detail... doesn't mean it suddenly becomes imaginary because of the name I happen to give it - now does it...!! You can object to the name 'centrifugal' if you like. That's your call. Whatever turns your crank I guess. I could argue that since this force (that we both agree is present AND perfectly real) is acting away from the centre of the circular motion and that centrifugal means 'centre-fleeing', that centrifugal is a perfectly sensible name for this particular force. ...but as we've already agreed -- this is all just semantics. ...what I really want to contest here is that I ever believed in any 'imaginary' forces - cos the fact is I never did. ...I think you heard the word 'centrifugal' and instantly thought 'imaginary'. But I don't think you really took the time to consider the exact force that I was actually talking about. (Which in fairness was in fact real - just as I said it was at the time...) Now, if you're going to call what I called the centrifugal force, the 'inertial force' of the person (i.e. use the source rather than the direction for the name), why is the term 'centripidal' still being used?! ...why aren't you ditching the term centripital too - and say the 'momentum of the car'..?' (Again, use the source rather than the direction?) ..how is it making things clearer to ditch the directional name for one force, but keep the directional name for it's counterpart?! ...I mean don't get me wrong, I'm sure there is a good reason. But instead of teaching me the evils of imaginary forces I never believed in in the first place, and re-itterating other princpiles of physics to me that I already perfectly understand - just explain to me, clearly and simply, why getting rid of the term 'centrifugal' force (which can be used in the context of a 'real' force - as I've just shown..) suddenly makes things so much clearer?! ...cos right now - to me - it's looking as clear as mud... Link to comment Share on other sites More sharing options...
ET Warrior Posted September 22, 2004 Share Posted September 22, 2004 Well I honestly cannot tell you WHY the name change, I was taught that there is no centrifugal force, and so I was unaware that it used to be taught that there WAS centrifugal force. However I DO realize that you understand newtons laws, and I feel a bit ashamed because I think I'm misleading you and quite possibly even giving you straight out WRONG information as far as centripetal force goes. I'm having a really hard time formulating the discussion about centripetal force into words now, I've sort of flustered myself, so later I might post some text out of my physics book and it may clear things up. Edit - Okay, here is the basic description of Centripetal force from my book Rounding a curve in a car. You are sitting in the center of the rear seat of a car moving at constant high speed along a flat road. When the driver suddenly turns left, rounding a coerner in a circular arc, you slide across the seat toward the right and then jam against hte car wall for the rest of the turn. What is going on? While the car moves in the circular arc, it is in uniform circular motion; that is, it has an acceleration that is directed toward the center of the circle. By Newton's second law, a force must cause this acceleration. Moreover, the force must also be directed toward the center of the circle. Thus, it is a centripetal force, where the adjective indicates the direction. In this example, the centripetal force is a frictional force on the tires from the road; it makes the turn possible. A centripetal force accelerates a body by changing the direction of the body's velocity without changing the body's speed There, the last quote basically sums up centripetal force, and I have been telling you quite wrongly and misinforming you. And for this I am quite sorry. Link to comment Share on other sites More sharing options...
RenegadeOfPhunk Posted September 23, 2004 Author Share Posted September 23, 2004 No worries ET. I dont' think you should blame yourself. It seems to me that nobody has a straight answer on this - not even the 'professionals'... Seems to me that this all came about because a lot of people used to use the term 'centrifugal' force inappropiately. (The example of the person sliding around in the car is the most obvious one). ...so I guess someone decided 'OK - let's just scrap this term - cos people aren't using it right.' OK, and I can understand this to an extent... But implying that ANY use of the term 'centrifugal' force must be imaginary (which to be fair, many [what you would have thought as] perfectly legitamete sources are saying - in such a way that this is the natural conclusion most sensible people would reach from what is written) is not accurate at all... ...you HAVE to look at the context in which the term is used before calling any instance of centrifugal force imaginary... And as far as the definition of centripital force: A centripetal force accelerates a body by changing the direction of the body's velocity without changing the body's speed ...phew! That's a relief. So I don't have to sue my school for teaching me crap in A-level physics then Cos that's how I understand it too Link to comment Share on other sites More sharing options...
iamtrip Posted September 23, 2004 Share Posted September 23, 2004 Can you just not agree that the force is flowing through us? Link to comment Share on other sites More sharing options...
ShadowTemplar Posted October 22, 2004 Share Posted October 22, 2004 A thread about physics? Wow! And I missed it? Damn! Link to comment Share on other sites More sharing options...
Dagobahn Eagle Posted October 22, 2004 Share Posted October 22, 2004 Isn't it already an estabilished fact that all objects going in a certain direction "want to go on in that direction"? What's there to debate? Link to comment Share on other sites More sharing options...
ET Warrior Posted October 22, 2004 Share Posted October 22, 2004 The debate was over whether or not there is such a thing as centrifugal force. I've actually come up with a good (at least I think so) description of why physicists use the term Centripetal and not centrifugal. The reasoning is that applying a force implies exerting something that will cause an acceleration, due to the law of nature Force = mass*acceleration. So lets look at the car example. The car turns, you fly outwards, the door holds you in and you push the door out. The door is accelerating you inwards, towards the center of the circle it is moving in. THIS is centripetal force, because it is actually accelerating you. Your push on the car door, while you ARE exerting a force, you are NOT accelerating the door, and therefore it is NOT centrifugal force Link to comment Share on other sites More sharing options...
Shok_Tinoktin Posted October 22, 2004 Share Posted October 22, 2004 The movement outwards in a circle is actually a matter of momentum, and not of force at all. The force that is applied to the door is a normal force, due to Newton's third law. The door is applying a force to you, so you are applying a force of equal magnitude and opposite direction on it. Link to comment Share on other sites More sharing options...
ET Warrior Posted October 22, 2004 Share Posted October 22, 2004 Yeah, we've already discussed that part of the laws into the dirt Link to comment Share on other sites More sharing options...
Spider AL Posted October 22, 2004 Share Posted October 22, 2004 Yeah, we've already discussed that part of the laws into the dirt Bluhhh, thread should never have been bumped by that darned ShadowTemplar... Link to comment Share on other sites More sharing options...
Dagobahn Eagle Posted October 22, 2004 Share Posted October 22, 2004 If you hit a car door, you transfer part of your energy into it and then use the rest to bounce back (if there's enough energy). Scientifically, gravity, too, is explained this way in a sense, too: You stay on the floor, which absorbs the energy that would otherwise make you keep falling. Clumsily put, but you know what I mean. Link to comment Share on other sites More sharing options...
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