Squeaky Friction

[BL4CKCR4Y0NS]

Main Question or Discussion Point

Why is it that when you pull out a cheap plastic drawer, there is sometimes a squeak that makes your ears bleed? (exaggerated.)

I know it has to do with friction but why does it squeak? Or rather, what causes the squeak?

If I run my finger down a surface, there is no squeak. Even if there is it's not nearly as high-pitched...

What's the difference between the two situations?

 

[Phrak]

Interesting. I'm going to hazard a guess that should be similarily true of the squeak a bow causes a fiddle string.

Becuase you have two similar materials--plastic drawer and plastic case the two materials tend to bind to each other.

The binding and break-away as you continue to pull the drawer sets up waves at the bind/break-away frequency. Binding occurs pulling the cabinet lip with it, it breaks-away oscillating in the opposite direction only to rebind when the velocites are a closest match. So I think it's the cabinet that vibrates, not the drawer. Maybe we should consult violin rosin manufactures about this.

 

[BL4CKCR4Y0NS]

Wow I didn't expect such an answer for such a simple question... nice :)

So may I ask, what is it that causes the binding of the drawer, and the cabinet?

 

[Phrak]

Wow I didn't expect such an answer for such a simple question... nice :)

So may I ask, what is it that causes the binding of the drawer, and the cabinet?

Remember, I'm just guessing about this. But if you were to visit the mechanical engineering folder and ask about similar vs. dissimilar materials in bearing surfaces, you might get a more informed answer. For instance, it may only be that bearing and journal should be dissimilar materials if they are metal, and I'm all wrong about plastics. Or it could just be that one surface just has to be a harder metal than the other. I'm not a materials expert, so I don't know much about it.

This is also about simple friction which is a more basic physics exercise than anything, unless you look at the microscopic level. The sliding friction between two surfaces is less than the static friction.