# Help in Homework -- difference b/w kinematics friction and static friction?

Hi,

Please explain what is the difference b/w kinematics friction and static friction ?

Please explain, what is rolling friction ?
Is it when we are pulling a weight with rope, and rope is rolling on a wheel ?
for example in past days, people used rope to get water from well.

Thanks.

Related Introductory Physics Homework Help News on Phys.org
berkeman
Mentor
Hi,

Please explain what is the difference b/w kinematics friction and static friction ?

Please explain, what is rolling friction ?
Is it when we are pulling a weight with rope, and rope is rolling on a wheel ?
for example in past days, people used rope to get water from well.

Thanks.
What do you think the difference is between static friction and dynamic friction? What do you find when you use Wikipedia or Google?

*.*.*AnUm*.*.*
I think static friction when any force causes friction
dynamic friction when a body is moving, right ?

berkeman
Mentor
dynamic friction when a body is moving, right ?
Yes. When the object is sliding, that is dynamic friction. When it hasn't broken loose yet to start sliding, that is static friction.

http://en.wikipedia.org/wiki/Friction

*.*.*AnUm*.*.*
Thanks :)

In other words,

• static friction between non-moving surfaces, and kinetic friction between moving surfaces, right ?

Is this explanation correct:

"Please explain, what is rolling friction ?
Is it when we are pulling a weight with rope, and rope is rolling on a wheel ?
for example in past days, people used rope to get water from well.
"

berkeman
Mentor
In other words,

• static friction between non-moving surfaces, and kinetic friction between moving surfaces, right ?
Yep!

*.*.*AnUm*.*.*
berkeman
Mentor
Is this explanation correct:

"Please explain, what is rolling friction ?
Is it when we are pulling a weight with rope, and rope is rolling on a wheel ?
for example in past days, people used rope to get water from well.
"
I think of rolling friction more like between a tire and the road. But I suppose it would also apply to a rope over a pulley too.

*.*.*AnUm*.*.*
Okey, thanks :)

And I think friction shouldn't be constant, is it correct ?

haruspex
Homework Helper
Gold Member
And I think friction shouldn't be constant, is it correct ?
Static friction can never be less than kinetic friction, but I know of no rule that says it has to be more.
In reality, friction is rather more complicated than is taught in school. But generally you are safe to say that each of the two coefficients of friction of a given combination of surfaces is constant, not varying according to normal force nor, in the case of kinetic friction, according to relative speed of the two surfaces.

berkeman
Mentor
And I think friction shouldn't be constant, is it correct ?