Talk:Circular motion

Switch of Variable?
Is there a particular reason that some equations in this article show angular velocity as ω and others use Ω? I find this confusing and it is not standard in the textbooks I have. I thought maybe the article is trying to emphasize the difference between the vector form and the scalar form of the angular velocity, but if that is the case then the acceleration a and radius r should also be capitalized as vectors. Inconsistency leads to confusion if there not a clear reason. If there are no objections in the next little while, I will go ahead and change this.

129.63.129.196 (talk) 19:13, 1 December 2011 (UTC)

Homework
Please send me some example of gravitational motion! a test with answer! unsigned

What about vertical circular motion, such as an outside, noncentripetal force? This article never mentions it, a link (which I cannot find) or an explination would be nice. --1698 2006 01 08 01:40 (PST)


 * I do not understand what you mean, how can a motion be circular without centripetal force?--Patrick 12:23, 8 January 2006 (UTC)


 * Vertical, as in there is a centripetal force and circular motion, but there is also gravity that is not centripetal.--1698 2006 01 08 12:45 (PST)


 * Good point, I added the more general case including this.--Patrick 01:23, 9 January 2006 (UTC)


 * Thank you very much...I was doing some homework actually ;). --1698 2006 01 08 19:00 (PST)

The explanation of the word 'centripetal' appears in the article centripetal force. It should not appear in this article. Bo Jacoby 07:36, 27 February 2006 (UTC)

Jerk
I'm curious about the jerk vector of circular motion. I know it must exist, because the acceleration vector is a first degree vector. Deriving the acceleration vector yields the vector (x(t),y(t)), where x'''(t) = Rw3sinwt, y'''(t) = -Rw3coswt. I would imagine that if the instantaneous displacement would be described by the circle of motion, the instantaneous velocity by a line tangent to the circle of motion in the direction of rotation, the instantaneous acceleration by a line from the circle of motion towards the center of motion, that the instantaneous jerk would be described by a point at the center of motion. That’s only conjecture on my part, and I really don’t know enough about the subject to add it into the article, but it would be interesting to see the result of someone who does to do so.

Answer
The position is z=Reiωt. Differentiation is d/dt=iω. Triple differentiation is (d/dt)3=(iω)3 = &minus;iω3. So instantaneous jerk is d3z/dt3=&minus;iω3z=&minus;iω3Reiωt. The numerical value of the jerk is |d3z/dt3|=ω3R. The direction of the jerk is opposite that of the velocity. Bo Jacoby 13:32, 7 August 2006 (UTC)

edit on Dec.4
Seems as though someone had some fun.

WikiProject class rating
This article was automatically assessed because at least one WikiProject had rated the article as start and the rating on other projects was brought up to start class. BetacommandBot 09:46, 10 November 2007 (UTC)

Concluding remark
Could someone explain the remark at the end of the article?

Using all of the above, a ball of 'r' radius rolling of a cylinder of 'R' radius will always come off the cylinder of 48.2 degrees ( cosx = 2/3), this will happen on any planet, and both R and r values can be anything, as long as air resistance is ignored.

I don't understand it. It seems to be referring to a concrete example details of which are details are missing. If it's making a useful point, it would be good to give it some more context. Dependent Variable (talk) 18:48, 31 March 2010 (UTC)


 * The sentence was edited by the original anon editor to read: Using all of the above, a ball of 'r' radius rolling off a cylinder of 'R' radius will always come off the cylinder of 48.2 degrees (cosx = 2/3), this will happen regardless on the mass of the ball, the gravitational strength, the two R and r values, as long as any type of resistance is ignored. The result is certainly true for a particle sliding without friction down a cylinder or sphere.  I'm checking out under what other conditions it remains true (I need to check moment of inertia).  I've removed it (partly because it doesn't belong in that section), but should it be put back with a better explanation?    D b f i r s   09:02, 5 May 2010 (UTC)

Merger proposal
It only makes sense to have just one article about Circular motion. There is no need for an article for each of the different concepts related to circular motion: uniform circular motion, Non-uniform circular motion, angular velocity, angular displacement, angular acceleration, Angular frequency centripetal force, and centrifugal force. I will attempt to do this in the next month year. sanpaz (talk) 21:38, 10 April 2010 (UTC)


 * That sounds a sensible suggestion, though perhaps the topics on centrifugal and centripetal forces could be separated to a linked article since they would form a sufficiently long article, and they apply to motion along other curves.   D b f i r s   22:33, 6 May 2010 (UTC)
 * I was thinking the same about centrifugal and centripetal forces. I agree with that. sanpaz (talk) 23:16, 6 May 2010 (UTC)


 * I think trying to have only one article for all of those topics will just lead to a confusing mess, especially when you add non-circular orbital motion (e.g. the Earth around the Sun), and try to cover both a point mass moving in a circle and a body spinning about an axis through its centre of mass. In my view, the best article above is uniform circular motion, which gives a fairly clear description of a relatively tightly-bounded topic.  (That's not to say that I think that we should keep all of these articles, just that I would prefer a less drastic merger proposal combined with a clear view on what the final goal should be.)  Djr32 (talk) 22:14, 1 June 2010 (UTC)
 * I don't think I am suggesting to merge any article about non-circular orbital motion. And there is also no suggestion to include rotation motion for rigid bodies. The only articles I am suggesting to be merged are uniform circular motion, Non-uniform circular motion, angular velocity, angular displacement, angular acceleration, Angular frequency. Let me know if I did not understand your point. sanpaz (talk) 16:05, 4 June 2010 (UTC)
 * Angular velocity, angular displacement, angular acceleration and angular frequency are just as relevant to the rotational motion of rigid bodies. My point about non-circular motion was badly expressed - I realise that you didn't mention this topic, but just as uniform circular motion is a special case of circular motion, it's also a special case of orbital motion, so it might be worth thinking about this area too.  Djr32 (talk) 21:16, 7 June 2010 (UTC)
 * I agree that the uniform and non-uniform circular motion articles can be merged. The other concepts are not exclusively related to circular motion though. They are used in non-circular contexts and would thus not fit well in an article regarding circular motion. However, they do cover rotational dynamics topics, so maybe those articles could be merged into an article along the lines of concepts in rotational dynamics. JHobbs103 (talk) 14:14, 5 June 2010 (UTC)
 * I have just seen that the centrifugal and centripetal force articles are included in this. They should not be merged. There is enough confusion surrounding those concepts without the articles being merged. JHobbs103 (talk) 14:31, 5 June 2010 (UTC)
 * ^Agree with that. Many people confuse centripetal and centrifugal. It helps to make things clearer. Melara... (talk) 22:52, 31 March 2011 (UTC)


 * I agree with Djr32 in that combining these would make a mess. There's a wealth of information on all these articles separately; merging them would make for a confusing article. —scarecroe (talk) 17:26, 16 June 2010 (UTC)


 * I am a student with a limited understanding of all these topics. I was just looking up angular frequency, because it relates to some of my reading on wave disturbances. I would be slightly confused if it showed up on wikipedia only as an aside within circular motion article. —Preceding unsigned comment added by 173.79.58.60 (talk) 04:44, 25 June 2010 (UTC)


 * Given the discussion above, I have reduced the scope of the merger proposal to just cover circular motion, uniform circular motion and non-uniform circular motion. Djr32 (talk) 12:10, 26 June 2010 (UTC)


 * Given the reduced scope of the merger proposal I now support it. Seeing as the discussion has taken a while, would you (Djr32) perform the task? JHobbs103 (talk) 00:02, 31 July 2010 (UTC)


 * I support it, too. I hope someone will get to it.  Dicklyon (talk) 00:27, 6 February 2011 (UTC)


 * I strongly support the latest proposal. I was appalled to find there were three separate articles on the same topic. MarcusMaximus (talk) 06:36, 7 July 2011 (UTC)


 * let it be as it is. Making a Joint topic will make it difficult to understand. mmshivesh 08:25, 25 May 2012 (UTC) — Preceding unsigned comment added by Mmshivesh (talk • contribs)

Merger of Circular motion, Uniform circular motion and Non-uniform circular motion
I would be pleased to take on the task of merging these three articles. Prof McCarthy (talk) 17:04, 5 January 2012 (UTC)


 * Go for it. I don't think anyone is particularly against the new proposal, and consensus is usually permission. 68.7.134.191 (talk)
 * Well, here's a start. It needs another hour or two to let out the lecture-hall droning and generally tighten up the language. A second reference might be useful for all that math, too. --Wtshymanski (talk) 03:42, 11 October 2012 (UTC)

Equations and Mathematical expression error
Equations and Mathematical expression are not displaying correctly in may sections, could someone please correct them. — Preceding unsigned comment added by Ahmer Jamil Khan (talk • contribs) 15:11, 27 August 2012 (UTC)

Non-uniform circular motion inaccuracies?
Fairly sure there are some inaccuracies in both wording and information. For example, the normal force should be perpendicular to the track. It should never appear to be diagonal. Anyone else with perhaps more expertise care to correct me or the article depending on which is wrong? 72.65.245.74 (talk) 01:06, 5 November 2012 (UTC)


 * The normal force is normal to the surface that constrains the motion, so it's perpendicular to the track in 3D, but not necessarily in the plane of the track. In that plane it can be "diagonal" if the speed is changing. Dicklyon (talk) 01:29, 5 November 2012 (UTC)


 * I believe that speed of an object should only affect the magnitude of the normal force, not it's direction. The normal force might be diagonal in a non Newtonian reference frame (certainly not my area of expertise), also perhaps if the plane you slice some 3D object in is weird. But in this specific case, the normal force should only point towards the center of the circle.72.65.245.74 (talk) 01:48, 5 November 2012 (UTC)


 * Sounds like you still haven't taken the hint of following the link and reading the definition of normal force.  Dicklyon (talk) 02:09, 5 November 2012 (UTC)

Labeling of figures is confusing. There are two 'figure 2'
The labeling of the figures in the article is confusing. It goes Figure 1, Figure 2, Figure 3, then for some reason it goes back to Figure 1 and Figure 2. In the article below (on the acceleration part) it refers to figure 2, which happens to be the first figure 2 , not the second figure 2. It took me a few minutes which Figure 2 it was talking about. It seems more logical to just label the second figure 1 as 'figure 4' and the second figure 2 as 'figure 5'. — Preceding unsigned comment added by 71.233.152.159 (talk) 05:29, 15 August 2014 (UTC)


 * I've changed the second "figure 2" to "figure 4". The two "figure 1"s are essentially the same.  Should we call them 1 and 1a?    D b f i r s   06:23, 15 August 2014 (UTC)

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Example wrong?
Hello,

I belief the example in the article is wrong: "Consider a body of one kilogram, moving in a circle of radius one metre, with an angular velocity of one radian per second." And that the resulting speed is 1 metre per second.

The formula above says that speed is defined as: Speed = 2 * PI * r / T.

T is in that example "2 seconds" (= it takes to seconds to do a complete turn of 360° = 2 rad). Radius is of course 1 metre resulting in a speed of Speed = 2 * PI * 1 metre / 2 seconds = 1 rad per second.

Since the speed is wrong, all other derived results (acceleration, centripetal force, ...) are also wrong.

Can someone check and correct it? — Preceding unsigned comment added by 194.114.104.118 (talk) 07:52, 10 September 2019 (UTC)

What is non uniform circular motion
When a fan is switched ON or OFF, the speed of particles of the fan go on increasing or decreasing for some time,  however their directions are always tangential to their trajectories. During this time, it is non-uniform circular motion. Rohan Gajbhiye (talk) 02:29, 15 July 2020 (UTC)

I't was really helpfull. Rohan Gajbhiye (talk) 02:33, 15 July 2020 (UTC)

Article issues and classification
The article fails the B-class criteria (#1 and #4). Far too much technical content and most of the article is unsourced. There is a 2019 "cleanup rewrite tag". -- Otr500 (talk) 17:10, 27 February 2023 (UTC)

Confused Lead
We seem to have ended up with a Lead that has some confused ideas likely to puzzle readers. This is an extract:

"'The rotation around a fixed axis of a three-dimensional body involves the circular motion of its parts. The equations of motion describe the movement of the center of mass of a body. In circular motion, the distance between the body and a fixed point on the surface remains the same. Examples of circular motion include: ... a ceiling fan's blades rotating around a hub'"

So the reader is encouraged to think about a ceiling fan. The equations of motion describe the movement of the center of mass of the body, which is presumably the middle of the axle in the middle of the fan, the one point that, in a properly-balanced fan, isn't actually going anywhere. So why do we have equations of movement to describe the one bit that isn't moving? And in circular motion, the distance between the body (is that the middle of the fan, which isn't going anywhere, or a point on the blades, which is actually moving in a circle) and a "fixed point on the surface" of what remains the same? A fan doesn't have a "surface". And in any case, in any rigid solid object, including ceiling fans, the distance between any fixed point on any part of it and any other fixed point, including its center of mass remains the same, no matter how it's moving. It would be true of the ceiling fan when it's turned off and not rotating. It was true of the ceiling fan when it was in the back of the electrician's delivery van, being driven in a straight line from the depot to the restaurant where it was finally fitted...

Is there any chance that someone who knows enough about the maths to avoid being instantly reverted could find a lead that actually makes sense to a reasonably intelligent but non-expert reader? Elemimele (talk) 18:36, 30 July 2023 (UTC)


 * ... I see it makes more sense if we consider the center of mass of each blade of the fan, which is moving in a circular path compared to the axis on which the fan is rotating. But so is every other part of the blade of the fan. And I still don't get what the "surface" means?? The center of mass of a fan-blade is highly unlikely to be on its surface - it isn't the surface of a simple cylinder either. What am I supposed to get from this mention of surfaces? Elemimele (talk) 18:40, 30 July 2023 (UTC)

Wiki Education assignment: 4A Wikipedia Assignment
— Assignment last updated by Kmijares (talk) 22:46, 15 November 2023 (UTC)


 * @Kmijares if you need any help, feedback, or advice don't hesitate to ask. In my opinion the thing this article most needs right now is better sources. If you could manage to find some excellent survey paper(s), book chapter(s), historical papers, etc. that would be amazing.
 * One concrete topic that would be worth discussing in a high-quality article about this subject is circular motion relative to different reference frames. For example, the historically oldest concept of 'circular motion' that was analyzed in detail is the apparent circular motion of the Sun and the stars relative to a horizon at a specific place on a spinning Earth. We now know that the stars are not actually undergoing a daily rotation about the celestial pole, and are instead (apparently) fixed when we change to a heliocentric coordinate system. –jacobolus (t) 23:11, 15 November 2023 (UTC)
 * Yes, the article is currently in a sadly under-referenced state. Any book called something like College Physics or University Physics will talk a lot about this. The ones from OpenStax are decent in my experience and have the advantage of being free online. XOR&#39;easter (talk) 04:09, 16 November 2023 (UTC)