Photo Contest - Kinetic Friction (10/12-10/18)

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Discussion Overview

The discussion revolves around the theme of a photo contest focused on kinetic friction, exploring what qualifies as kinetic friction in various scenarios. Participants are sharing their interpretations of the contest rules and debating the inclusion of different types of friction, particularly in relation to fluid dynamics and static versus kinetic friction.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that a flying aircraft, particularly during landing or take-off, could illustrate kinetic friction due to the interaction between the wings and air.
  • Others argue that air or wind drag does not qualify as kinetic friction, noting that it is typically not considered in general physics contexts.
  • A participant expresses uncertainty about distinguishing between static and kinetic friction in a static image, suggesting it is a challenging problem.
  • There is a discussion about the definition of kinetic friction, with references to physics texts that describe it as forces acting between surfaces in relative motion.
  • Some participants clarify that air resistance and drag do not constitute kinetic friction, as gases lack surfaces in the context of this definition.

Areas of Agreement / Disagreement

Participants do not reach a consensus on what constitutes kinetic friction, with multiple competing views regarding the inclusion of fluid drag and the definitions of friction types. The discussion remains unresolved on these points.

Contextual Notes

The discussion highlights limitations in definitions and the application of concepts, particularly regarding the distinction between kinetic friction and other forms of resistance like air drag and rolling friction.

ZapperZ
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Kinetic Friction

Kinetic friction is friction that occurs when something is moving and rubbing against another surface, creating such a friction. Your photo must clearly depicts a scenario in which such a thing is occurring. In includes cases where the friction is present but minimal, such as in ice skating.

Contest Rules:

1. Any digital photo or digitally-scanned photo relevant to the theme will be accepted within the contest period. In case there's a gray area, or you're not sure if the picture is suitable, check with me first.

2. Size limitations: Your photo is only limited to the file size limitation set by PhysicsForums. However, your may want to consider reducing the size of your photo if the file size exceeds 1 Mb. If your file is being hosted elsewhere, I will have to see how it is being displayed here, and I may ask you to resize and resubmit if it causes problems.

3. Upload your photos to any of the photo servers such as imageshack or photobucket. Then post it the relevant contest thread and link your picture using the img command. PM me if you do not know how. Alternatively, you may simply upload your image file to PF, and then have the full image displayed in your post.

4. Only ONE picture per member per contest. Once a picture is posted, it cannot be changed other than a total withdrawal by that member from that week's photo contest. Exceptions will be made for modification to comply with the rules, such as resizing.

5. At the end of the contest period, I will open a poll and every PF member can vote for the picture they like best.

6. Note that in case we have a large number of entries, I will do the polling in more than one thread. If that's the case, you can vote in each of the polling threads. The photos will be assigned in the polling threads in the order they were submitted.

7. The photo of the subject must be something that you took directly, not via in intermediary medium, and not taken by someone else. Unless otherwise noted, a photo of another photo, painting, print, etc. does not qualify.

8. You can use a picture only once. Once it is used in a contest, it cannot be reused in another contest.

9. Please post only pictures meant for submission in this thread. Photos not meant for submission must not be posted in the contest thread. Posting of more than one photos by a member may result in an automatic disqualification from the week's contest.

Zz.
 
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ZapperZ said:
Kinetic friction is friction that occurs when something is moving and rubbing against another surface, creating such a friction. Your photo must clearly depicts a scenario in which such a thing is occurring.
A flying aircraft or one that is about to land or take-off will count, considering the friction between the wings and air?
 
Wrichik Basu said:
A flying aircraft or one that is about to land or take-off will count, considering the friction between the wings and air?

This is a great question, as I have lots of great pics showing fluid drag in various cases, but was unsure whether fluid drag would count as "kinetic friction" for the purposes of the contest. Due to the uncertainty, I went with a classic ice skating photo of my daughter.
 
Wrichik Basu said:
A flying aircraft or one that is about to land or take-off will count, considering the friction between the wings and air?

No, air or wind drag does not count. We don't normally, at least in a General Physics course, consider those as kinetic friction. Air resistance varies with speed. Kinetic friction does not.

Zz.
 
ZapperZ said:
No, air or wind drag does not count. We don't normally, at least in a General Physics course, consider those as kinetic friction. Air resistance varies with speed. Kinetic friction does not.

Zz.

For me, the trick is to (somehow) distinguish static and kinetic friction while using a static image. Interesting problem...
 
  • #10
Andy Resnick said:
For me, the trick is to (somehow) distinguish static and kinetic friction while using a static image. Interesting problem...

Yes, the photo must give a clear impression that the object is sliding, and not simply static. It isn't trivial.

Zz.
 
  • #11
Sometimes, just posing a question stimulates an answer:

DSC_4569 copy.jpg
 
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  • #12
marzena_kinetic_friction.JPG
 
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  • #13
lekh2003 said:
A wheel rolling without slipping uses static friction, not kinetic friction. Is he braking? :oldwink:
 
  • #14
morrobay said:
lekh2003 said:

Unfortunately, I do not see the connection with kinetic friction in these two photos. Wind resistance, as has been stated, is not considered as kinetic friction, and neither is rolling friction, if the bike isn't skidding.

Zz.
 
  • #15
Well I certainly am not debating any physics PhD's here but in my Halliday-Resnick text: Forces acting between surfaces in relative motion are called forces of kinetic friction". Then since the oxygen and nitrogen molecules are in motion along the towel surface...
 
  • #16
morrobay said:
Well I certainly am not debating any physics PhD's here but in my Halliday-Resnick text: Forces acting between surfaces in relative motion are called forces of kinetic friction". Then since the oxygen and nitrogen molecules are in motion along the towel surface...

And air resistance is not such a force. Gasses have no "surfaces", so by the definition that you are using, air resistance and drag do not have kinetic friction.

zz.
 
  • #17
Thai massage
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  • #18
Final day to submit your photo for this contest.

Zz.
 
  • #19
Sorry guys :P, I guess I stretched it. It's alright.
 

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