Comments on: Will an object ever stop because of friction

By: tdzxtdzx

tdzxtdzx — Wed, 26 Aug 2009 22:04:52 +0000

By: T.

T. — Fri, 17 Jul 2009 23:12:58 +0000

Doug:

Because we are talking about the effect of friction over a *moving* object, static friction is irrelevant in this situation.

Dynamic friction clearly depends on velocity, and that’s about all you can say about it in a general way (that and the fact that it opposes movement). Postulating that friction is directly proportional to velocity is a simplification — one frequently used in physics problems. I only did so in order to be able to arrive at a concrete result. But, as I pointed out, my conclusion generalizes to cases where the dependence is something other than a linear function.

I’m not sure what you mean when you say that the dynamic frictional force is required to keep an object moving at a constant speed. In fact an object will move at a constant speed if there is no force at all (or if the resultant of all forces is zero).

By: admin

admin — Fri, 26 Jun 2009 12:16:29 +0000

Thanks for your response,

Frictional forces may not be proportional to the velocity but they clearly depend upon it a increase and as the velocity increases. Does static friction have an effect in this situation since there isn’t a force being applied to the object to start it moving?

My main point in this post is that when no force is being applied to an object and it is at rest the frictional force is 0 so as a moving objects velocity is reduced and tends to 0 the frictional force that it is experiencing is also reduced and also tends to 0 so it would appear the fictional force could never bring the object to rest.

thanks again for your comment,
David

By: Doug Jenkins

Doug Jenkins — Wed, 24 Jun 2009 23:14:01 +0000

It seems to me that the response from T is overcomplicating the problem. Frictional forces are in general not proportional to velocity, in fact the static frictional force (the force required to get a static object moving over a rough surface) is usually greater than the dynamic frictional force (the force required to keep it moving at a constant speed).

By: AgekEurorge

AgekEurorge — Thu, 21 May 2009 02:36:27 +0000

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By: Codsperee

Codsperee — Wed, 20 May 2009 06:13:01 +0000

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By: T.

T. — Mon, 18 May 2009 17:56:55 +0000

I’m actually from Portugal. I’m 22 and about to finish a Master’s degree in Electrical Engineering. Besides that I have a strong passion for mathematics and computer programming.

You do cover advanced stuff in comparison with us here in Portugal; I wasn’t taught anything about integrals before University (much to my dismay). We really should have our curricula revised.

Best of luck with your studies!

By: admin

admin — Mon, 18 May 2009 14:48:19 +0000

Im doing A level maths and further maths at the moment with the hope of starting university in October (ill be 18 in july). I live in the UK but im not sure how that converts to american stages of education(Im guessing your american simply on the basis that the majority of people on the internet are).

If your interested below is one of last years pure maths papers so you can see the level of covered ive covered.
http://www.wjec.co.uk/uploads/papers/s08-979-01.pdf

Dave

By: T.

T. — Mon, 18 May 2009 13:48:42 +0000

No problem! Meanwhile I re-read my reply and noticed a couple of errors (an extra minus sign in (1), v’ instead of dv/dt, P(x) instead of P(t)), but I think they were fairly easy to spot.

If I may ask, what is your level of education? From the title of your blog it seems you are in high school, but you do cover slightly more advanced stuff.

By: admin

admin — Mon, 18 May 2009 10:15:19 +0000

Thanks for your detailed response,
Both of your explanations seem to offer a good explanation so thank you for the response.

David