IIT JEE , AIEEE Forum - Physics , Mechanics

nikki.411

hey can ne1 temme dat wat will b d direction f d force of friction on a rolling body moving:

1. up the inclined plane.

2. down the inclined plane.

i wan a perfect answer 4 dis.....

nikki.411

plzzz ans dis one yaar.....

kahan ho sab????

helloooooooooooooooo....

ksgandharva

well.. it depends on the way the rolling body rolls.. if it rolls perfectly without slipping.. the direction of friction will be down the plane when it rolls up.. and vice versa.. because note the direction of the point of the rolling body that is in contact with the surface.. frictional force will be opposite to it!.. hmm is my answer correct?? rate me!

akshay.khare91

In case of rolling friction always tries that there should be pure rolling
..i.e. always v=

R...

if the body is moving up the incline then due to mgsin

the velocity of body goes on decreasing and there is no force which can increase its velocity therefore friction acts in same direction in which body is moving that is upwards so as to increase v
therefore the body can follow v=

R.

however if the body is moving down the incline then due to mgsin

its velocity goes on increasing and there is no force which has torque about COM.. so friction
acts in opposite direction in which the body is moving so as to decrease v and to
provide a torque which will increase

... so as to follow v=

R.

sidsgr88

dir of friction???
WELL IT DEPENDS .. if the body is rollin up or down and the rolin is pure then the dir of friction cant b determined coz its static friction
if the rollin is not pure then the dir of friction is determined in the same way as in normal horizontal surface

abhishekray07

the direction of friction for a rolling body is always up the incline

saurabh_reincarnated

ya rit.....

if body is pure rolling direction is always up the inclined plane......

but if body slides ...... th friction will oppose relative motion......

Cheers!!!!!!!

sutapadey

while the body is rolling up, the friction willk act up the plane and while the body is rolling down thr friction will act downward only if the case is of pure rolling.

saurabh_reincarnated

why guys........

u see everyone can understand that friction will be upwrd while moving down

but while moving up see the frce mg sin theta acts at COM and cause speed of body to decrease ......... due to extrnal frce

now to satisfy v= r omega ......... omega must also decrease

now...... for omega to decrease we need to hve a torque........ and mg sintheta

can apply no torque bcos its acting on COM.....

so the trque is provided by friction........ and it acts in such a way to decrease omega.....

so u can now realise that here also friction acts in upward direction,,,,,,

hope this helps .........

Cheers!!!!!!

jasss

in both the cases friction acts in the upward direction.
when the body is moving down the incline,acceleration is downwards,hence the lowermost point has the tendency to go downwards---friction acts in the upward direction
wen the body is moving up the incline since the torque due to all other forces is zero,that means no forcehas got the tendency to make the body roll,hence a friction force has to act to make the body roll,now 4 the direction,see that acceleration of the body is downwards hence the angular acceleration should be anti clockwise n dat's possible only wen friction acts upwards.................
for the direction of friction always keep 1 thing in mind...try to predict the direction in wich the lowermost point of the body has the tendency to go.....friction acts in opposite direction..........i hope its useful

Ask & Discuss Questions with Community & Experts