Things I just don't get....

[Cardinal Fang]

7. [size=+1]Why does friction increase with roughness to a point and then start to decrease with increasing roughness.
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Thanks to all those that responded to me in PM. Yes you were all correct. I was using the f=(coeff. of friction)xN to describe friction in my statement. Where N is the normal force it is equal to the weight or load of the object if it is sliding on a level surface. I didn't realize friction was far more complicated.

 

[auto doctor]

7. [size=+1]Why does friction increase with roughness to a point and then start to decrease with increasing roughness.
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Think of it like rough sex..

 

[great bear]

Things I don't get.

1. Why do members say "PM me" when they can just send a PM to start the conversation?

2. Why was Idle Ramblings so popular?

3. Sex.

In things you don't get. Goober as long as you don't get a call from your doctor that your tests came back positive for STD's that's a call you don't want to get.

 

[Cardinal Fang]

careful doc, you'll turn him on

He had me at "hello."

 

[Goober Mcfly]

4. Why do I keep getting Cardinal Fang's results in this online personality test? Click

 

[auto doctor]

careful doc, you'll turn him on

Fang...just close your eyes and call out Kathy...oh Kathy...baby.

 

[eyeofthedragon]

He had me at "hello."

wasnt it in the jello?

 

[raverboy]

Thanks to all those that responded to me in PM. Yes you were all correct. I was using the f=(coeff. of friction)xN to describe friction in my statement. Where N is the normal force it is equal to the weight or load of the object if it is sliding on a level surface. I didn't realize friction was far more complicated.

What I dont get:

Why you first defined friction by...

F = μ*N where
F = Frictional Force
μ = coeff. of Friction
N = Normal Force exerted by object perpendicular to level surface, ie its weight,

then say that you "didnt realize friction was far more complicated". You've already defined it.

Now, back to #7 of your "don't get's":

7. Why does friction increase with roughness to a point and then start to decrease with increasing roughness.

That's because all materials have a distinct coefficient of friction (assuming a smooth surface in that material) dependant on their material properties.

When considering those same materials with "rough" surfaces, friction, in general, would decrease as contact area decreases (the latter being a result of increased "roughness"). For any material with a "rough" surface, I am sure one can devise a second-order function between each and any of its surface roughness units (Rq, Ra and Rm, in microns) and the corresponding coefficient of friction.

Yeah, I've got too much time on my hands, but not that much!

 

[auto doctor]

wasnt it in the jello?

Floppy in the jello with fang.... Talk about a pair wet noodles

 

[Berlin]

69. freebies.

 

[Berlin]

Yeah, I've got too much time on my hands, but not that much!

... hmm.. got free time ? How about some Quebec porn links ?

 

[shakenbake]

What I dont get:

Why you first defined friction by...

F = μ*N where
F = Frictional Force
μ = coeff. of Friction
N = Normal Force exerted by object perpendicular to level surface, ie its weight,

then say that you "didnt realize friction was far more complicated". You've already defined it.

]QUOTE]

Who the fark cares, unless it's the right type of friction, skin to mucus membrane!

 

[red]

paying for sex

 

[eyeofthedragon]

static friction or kinetic?

 

[raverboy]

Who the fark cares, unless it's the right type of friction, skin to mucus membrane!

True. μ = oh, about 0.01?

 

[raverboy]

... hmm.. got free time ? How about some Quebec porn links ?

Sure!

 

[eyeofthedragon]

Friction and Surface Roughness

In general, the coefficients of friction for static and kinetic friction are different.

Like all simple statements about friction, this picture of friction is too simplistic. Saying that rougher surfaces experience more friction sounds safe enough - two pieces of coarse sandpaper will obviously be harder to move relative to each other than two pieces of fine sandpaper. But if two pieces of flat metal are made progressively smoother, you will reach a point where the resistance to relative movement increases. If you make them very flat and smooth, and remove all surface contaminants in a vacuum, the smooth flat surfaces will actually adhere to each other, making what is called a "cold weld". Once you reach a certain degree of mechanical smoothness, the frictional resistance is found to depend on the nature of the molecular forces in the area of contact, so that substances of comparable "smoothness" can have significantly different coefficients of friction.

An easily observed counterexample to the idea that rougher surfaces exhibit more friction is that of ground glass versus smooth glass. Smooth glass plates in contact exhibit much more frictional resistance to relative motion than the rougher ground glass.

 

[great bear]

I'm bored to ratshit. Is it just me or is nothing happening today?

 

[Goober Mcfly]

I'm bored to ratshit. Is it just me or is nothing happening today?

Quick! Look out the window! Look! Look! No the other one!










Awww, you missed it.

 

[great bear]

My windows have gummy bears stuck to them.