High School Question about Friction

[JasonRox]

If the coeficient of friction is 0, than I don't need any force to push it?

If it is .5, I only need to push 50% of it's total vertical force?

I think I got this right.

Which is why sliding is sometimes more efficient than lifting, right?

If something had a coeficient of 1.5, you are better off lifting it off the ground.

 

[Alkatran]

The friction coefficient is not the percent of force which is resisted, it's the ratio between the force between object/ground and friction.

For example, you know that gravity accelerates everything downwards at 9.8 m/s^2 so if we had a 5 Kg block sitting ona surface with a coefficient of 2:

Friction = Fn * u
Fn = -Fg
Fg = -9.8*m
Friction = -Fg * u = --9.8*m*u = 9.8*5*2 = 98 Newtons

So if you push the block, you need to push with more than 98 Newtons to accelerate it.

 

[HallsofIvy]

"The friction coefficient is not the percent of force which is resisted, it's the ratio between the force between object/ground and friction."

But that's what Jason Rox said: " 50% of it's total vertical force?"

Essentially, yes, in order to keep something moving at a constant speed on a horizontal surface, you must apply a force equal to the friction force which is the friction coefficient times the "total vertical force".

 

[Gokul43201]

I doubt you'll ever come across a pair of surfaces with mu = 1.5.

 

[JasonRox]

It's been awhile, but in the end, because frictional force rarely goes above it's vertical force, everyone chooses to slide big objects.

 

[Chen]

I also thought that μ is limited to be between 0 and 1, but some websites list coefficients with values greater than 1:
http://www.carbidedepot.com/formulas-frictioncoefficient.htm
At the same time some websites say this isn't possible, so I don't know what to believe.

 

[JasonRox]

It is possible, but it is unlikely.

Friction exists because surfaces are uneven if you look REALLY close. You see little bumps, which the object must overcome to slide across the surface.

So if the surface consisted of walls, like a maze, it would be quite difficult to slip a television through without going around the walls. In the end, the bigger the bumps, chances are the coeficient of friction is higher.

 

[cookiemonster]

Try putting two pieces of glass on each other...

cookiemonster