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Mechanics

New kid on the Block

 Joined: 24 Jun 2009 Post: 6
1 Apr 2010 00:34:58 IST
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When we walk the work done by friction is negative or positive....?
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When we walk the work done by friction is negative or positive....?

Cool goIITian

Joined: 26 Mar 2010
Posts: 65
7 Apr 2010 07:09:47 IST
1 people liked this

@Optimus

Friction i a non conservative force and it is path dependent. So then we walk.... How do you walk... push the ground behind and the ground pushes you forward... now the friction is between your feet and ground. now when you push the ground the friction should have a direction in the direction opposite to that of the relative motion of your feet else you would fall down. So friction acts in the forward direction. But when the ground pushed you back.... the point of application of force loses contact so the change in direction of friction doesn't come into play. Hope fully you must have got it....

Cool goIITian

Joined: 4 Apr 2010
Posts: 48
7 Apr 2010 08:40:24 IST
0 people liked this

What are you trying to say? Read my answers once more please, I am making a similar point, I am not considering any change in the direction of the frictional force. And this does not answer the question here. And the doubt was never mine, I was just trying to clear it for the one who asked.

Blazing goIITian

Joined: 11 Apr 2009
Posts: 672
7 Apr 2010 08:41:41 IST
1 people liked this

told him the same thing in his nudgebook!!!......and where are the mods !!...can ne 1 delete viper's post !????  ...plzz! ..its unbearable!

Blazing goIITian

Joined: 15 Nov 2009
Posts: 608
7 Apr 2010 16:54:21 IST
0 people liked this

yup mods plz do sumthing about viper's post

Hot goIITian

Joined: 25 Sep 2009
Posts: 178
7 Apr 2010 17:36:37 IST
1 people liked this

hey frnds dont consider it.let this viper bark whatever he wants to...

New kid on the Block

Joined: 5 May 2013
Posts: 2
5 May 2013 13:50:29 IST
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in which direction the friction acts when we walk.?

New kid on the Block

Joined: 5 May 2013
Posts: 2
5 May 2013 13:52:58 IST
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in which direction the friction acts when we walk.?

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:12:04 IST
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AFTER SO, MANY CONFUSING DISSCUSSION, LETS DO IT PRACTICALLY.....Take your slipper and on the sole put a drop of viscous fluid like ink. now put on the slipper, and carefully stand, now move 3-4 steps......

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:16:50 IST
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now, take wear only one slipper at a time, and do walk, and repeat the walking by another slipper by wearing it.

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:18:11 IST
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make insure that your have marked the mean position of centre of ink, by the pen showing its position by arrow.

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:22:15 IST
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OBSERVATION: you will observe that the ink will flow (blot) to forward side of sole much larger and a very little backward. so, we can conclude that upper layer of in contact with ink is a rest while that with ground is experiencing a viscous drag due to friction in FORWARD (because most of the ink will flow forward)....so, the ground friction will act forward.

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:24:47 IST
0 people liked this

so, final conclusion, and Answer is that, as ink flow tells that there occured displacement in forward much more than that at backward. so, net work done is always positive, and can never be negative.

Scorching goIITian

Joined: 10 Oct 2012
Posts: 237
5 May 2013 14:33:41 IST
0 people liked this

now, those who say that the point of contact is at rest... its just ideal, in real, you can't walk properly, if the point of contact will be at rest as you will get jerk in your motion....................in real world, there occurs a little displacement of point of contact......... the point of contact experience max displacement on slippery surface,,,, and minimum, but not zero.... ..... i , better give you example.... you are walking on hard soil, in usuall manner , suddenly a swampy, wet soil(the crust is very weak) ...you cant walk on it with your slipper and you would require to take it on your hand.... but in this case too, where the earth crust is slightly smooth, or water is not absorbed properly,, you will experience sudden slipping,,, and you are required to take the smaller steps there to ensure minimum displacement of point of contact.................hope you all understood...

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