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

[*.*.*AnUm*.*.*]

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.

Please explain it.

Thanks.

 

[berkeman]

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.

Please explain it.

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]

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 :)

 

[*.*.*AnUm*.*.*]

In other words,

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

 

[*.*.*AnUm*.*.*]

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]

In other words,

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

Yep!

 

[berkeman]

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 :)

 

[*.*.*AnUm*.*.*]

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

 

[haruspex]

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]

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

The wikipedia article that I linked to earlier in this thread answers that question.