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21 Dec 2007 14:30:35 IST
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Shreya
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21 Dec 2007 14:54:43 IST
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ya, it acts as rolling friction also exists
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21 Dec 2007 15:28:57 IST
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Yes, the force of friction acts tangentially to the surface of the rolling body at the point of its contact with the surface (point A in the diagram above).
The force of friction mainly depends upon the area of the body in contact with the surface. In case of a pure rolling body the area under contact with the surface is very negligible, therefore the frictional force acts tangentially.
The only reason why we use wheels in cars for fast transportation.
22 Dec 2007 17:23:35 IST
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IN PURE ROLLING..THERE IS NO FRICTION!!!! JUST ..THINK THIS WAY... WAT IS VELOCITY OF PT OF CONTACT...V-WR...TAT IS 0000000000 SINCE PURE ROLLING...SO WEN THERES NO MOTION ..Y SHD FRICTION..ACT.....
IM QUITE CONFIDENT TAT IM RIT...SO PLZ...RATE ME!!!!
IM QUITE CONFIDENT TAT IM RIT...SO PLZ...RATE ME!!!!
22 Dec 2007 20:57:21 IST
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Friction opposes relative slipping. Refer the figure.
It is clearly seen that the point A moves backward, ie, after the wheel is set into motion. Hence to prevent this relative slipping, friction acts in the forward direction.
If the wheel were slipping with zero angular velocity, then the frictional force would act in the forward direction
23 Dec 2007 00:07:46 IST
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@ Indzee,
The force and friction in this case act in the forward direction. Here's my argument.
When F acts on the sphere, the sphere has an angular acc. which gives it a tendency to slip on the suface and not move as in pure rotation. Imagine, when you apply brakes on a slippery ground, your wheels retard faster than stop revolving and hence there is slipping and pure rolling does not occur.
Friction acts to stop this slipping tendency and hence acts in the same direction as the force F.
Also, if friction acts in the backward direction, the wheel will have a very high torque, giving it a higher angular acc. but since the forces act in the opposite directions, acceleration will be less. hence, there'll be slipping.
Hope its clear now
The force and friction in this case act in the forward direction. Here's my argument.
When F acts on the sphere, the sphere has an angular acc. which gives it a tendency to slip on the suface and not move as in pure rotation. Imagine, when you apply brakes on a slippery ground, your wheels retard faster than stop revolving and hence there is slipping and pure rolling does not occur.
Friction acts to stop this slipping tendency and hence acts in the same direction as the force F.
Also, if friction acts in the backward direction, the wheel will have a very high torque, giving it a higher angular acc. but since the forces act in the opposite directions, acceleration will be less. hence, there'll be slipping.
Hope its clear now
23 Dec 2007 21:11:03 IST
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@ karthik_karthik9920
Check this.
If there was no friction, there would be slipping between the surface and ground.
I'll give the same example I gave to explain it to Indzee. On a slippery ground, the sphere or a wheel will not be in complete rotation ( i.e.
r*v) This is because there is slipping between the surfaces and there is less friction to keep the body in pure rotation.
Also, friction acts to prevent relative motion between two bodies, this doesn't imply that if there's no motion, there is no friction. Imagine this, when you push a block on a rough surface, there is no motion initially, but still friction acts
Why do we say that friction acts? Not because the bodies are moving, but becoz there 's a tendency of relative motion. Had there been no friction, the body wud have moved.
I hope its clear now.
PS : rate me if I'm correct
Check this.
If there was no friction, there would be slipping between the surface and ground.
I'll give the same example I gave to explain it to Indzee. On a slippery ground, the sphere or a wheel will not be in complete rotation ( i.e.
r*v) This is because there is slipping between the surfaces and there is less friction to keep the body in pure rotation.Also, friction acts to prevent relative motion between two bodies, this doesn't imply that if there's no motion, there is no friction. Imagine this, when you push a block on a rough surface, there is no motion initially, but still friction acts
Why do we say that friction acts? Not because the bodies are moving, but becoz there 's a tendency of relative motion. Had there been no friction, the body wud have moved.
I hope its clear now.
PS : rate me if I'm correct
24 Dec 2007 12:50:59 IST
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@karthik
no, man. consider this case. a ball is placed on a rough inclined plane. due to gravity, it is set into motion down the incline. your argument is that friction acts in the direction down the incline. this results in a clockwise torque that tries to stop motion.
consider this. according to ur argument, a cube and a ball of the same material and mass would take the same time to come down the incline. is that what really happens?
25 Dec 2007 19:13:41 IST
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Yes, in case of pure rolling the force of friction acts
Let us consider a example
IF a body is rolled and placed on a surface with friction and also we have given
it a velocity then if V> then friction force acts in backward direction to
provide it a torque and increases it angular velocity so that v=r.
And if V< then friction force acts in forward direction to reduce angular velocity
so that again v= r...
and if we are performing the above experiment on a inclined plane so that
Mg has two components Mgsin
and Mgcos .Since Mgcos
is balanced
by normal reaction and it has no torque. Also Mgsin has no torque
therefore there is only frictional force which will provide a torque and
will cause pure rolling v=r
however work done by frictional force is zero
Let us consider a example
IF a body is rolled and placed on a surface with friction and also we have given
it a velocity then if V>
then friction force acts in backward direction to provide it a torque and increases it angular velocity so that v=
r. And if V<
then friction force acts in forward direction to reduce angular velocity so that again v=
r...and if we are performing the above experiment on a inclined plane so that
Mg has two components Mgsin
and Mgcos .Since Mgcos is balanced by normal reaction and it has no torque. Also Mgsin
has no torquetherefore there is only frictional force which will provide a torque and
will cause pure rolling v=
rhowever work done by frictional force is zero
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