a bicycle moving on road .

here friction does + work on bicycles wheels.

 One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the frame of reference in which the floor is stationary. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work .......................this is given in wiki and autobot also posted dis in an earlier reply !!......NOW WHAT I CAN DO IS EXPLAIN THIS !.....SEE IF AN OBSERVER IS DERE ON THE RUG ( JUST IMAGINE) .....FOR HIM THE BOX IS MOVING BACKWARDS !......BUT IF SUM1 IS STANDING ON THE FLOOR THE FOR HIM THE BOX IS MOVING IN THE DIRECTION OF FRICTION FORCE ONLY ...NOW WHEN WE COMMPUTE WORK IT COMES TO BE POSITIVE ....this example is given in wiki ...i am gonna draw it for u !!..plzzz wait ! .. in the meanwhile ppl plzz give sum more examples ! 

@Akash:  Wrong example dude, sorry.

As posted in the other thread too : http://www.goiit.com/posts/list/20/mechanics-when-we-walk-the-work-done-by-friction-is-negative-1013453.htm

 Wiki says:

Friction can do positive work in certain frames of reference. Though the net work done by it from ground frame would still not be positive. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the frame of reference in which the floor is stationary. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.

 I AMTALKING ABOUT THE FRAME ONLY ! 

friction could +ve work it only depend on the frame of refrence only

 When we walk..... friction does positive work...

 ^^^^^ very wrong !!!!...see my example !!!! and also see dis !  http://www.goiit.com/posts/list/mechanics-when-we-walk-the-work-done-by-friction-is-negative-1013453.htm

 when you walk we push the ground back but the friction tries to oppose the motion and acts in the forward direction. So the work done becomes positive.

 plzz yaar see the link i gave u !...i have explained dere!..and many other ppl hav also explained ..plzz see!

Consider a solid sphere on an inclined plane in a state of pure rolling.

Here, the friction force acting between the surfaces of the sphere and inclined plane produces a torque which increases the rotational kinetic energy of the sphere.

Here, it's clearly observed that work done by friction = change in K.E = K2-K1 . As explained above K2>K1. Hence work done by friction --> +ve.

I sort of agree with insomaniac. Yaar.. the points I have raised were never answered in that post.. i didnt understand a bit what optimus said. Sorry dude ur replies are way to long and cover too many points .. Its strange but I just didnt get u :O.

See this post

http://www.brighthub.com/education/k-12/articles/35149.aspx

It also claims friction does positive work when we walk. And the fbd there was the FBD i initially had in my mind but I messed it up with rotatory motion concept.

Yeah dude..

see the site I posted and see the FBD there.. I slightly modified that and animated it. see that and tell me if u still feel friction does no work when we walk

Quoting from YOUR given link:

.................Since the foot does not move, the force is static friction and not dynamic friction

.................the work in walking is done by the internal muscular forces of the leg.

.................The work done in moving the body forward and dissipation as heat by friction is done by the backward pushing force of the leg muscles.

.................The leg and the body moves forward but the foot remains stationary.

And its not about what I feel, friction actually does no work when we walk.

Please answer these 2 questions:

When we walk, we fix our leg on the ground, and push, right? Then

1) Does the fixed leg move for the duration in which we push?

2) Is that leg still in contact with the ground when we lift it and put it forward?

WHAT THE HELL only look at the FBD.

Text is pure BS. We do move our foot when we walked. I WALKED FOR HALF AND HOUR AND OBSERVED VARIOUS FORCES.

We move our leg backwards but our torso moves forward. since the whole body moves forward. and force of fricition is forward work done is positive.

Thats a very strange walking u do.. We humans do move our leg back.. u auto bots well .. use TYRES !!

ANYWAYS ENUF OF THIS STUPID SCENARIO YAArr.. I bored.. lets fight on some other question

Then I guess you humans, would include you and Michael Jackson, and since he can't moonwal-- *cough* walk now, its only you.

I give up, Its beyond my powers to explain this to you, so you keep whatever concept you want to keep.

For anyone else out there, looking for an answer.

FRICTION DOES NO WORK WHEN WE WALK.