# Question about friction

1. Feb 23, 2008

### shayrgob

In my physics book it says: "If there were no applied force (F), then Static friction force will be 0."

What confuses me is this, what if an object was sitting on a conveyer belt moving at a 30 degree angle, for instance. What causes that object to remain on the conveyer belt? obviously the friction between the object and the belt? Am i mixing up coefficient of friction and static frictional force?

thanks for your time

2. Feb 23, 2008

### arildno

Gravity then plays the role of applied force (i.e, a force from somewhere else acting upon the object ALONG the surface).

3. Feb 23, 2008

### shayrgob

yeah but what if you change the material being used for the conveyer belt? Then obviously more variables (besides the weight of the object) are introduced. Let's say that a smoother surface is used. The object will now slide down.

4. Feb 23, 2008

### arildno

How does that change gravity from being the "applied" force which was what you were asking about?

5. Feb 23, 2008

### Staff: Mentor

Yes. That's dynamic friction. [response was to shayrgob]

Last edited: Feb 23, 2008
6. Feb 23, 2008

### arildno

Even if the object slides down, graviry is still to be regarded as the "applied" force.

7. Feb 23, 2008

### shayrgob

wanna elaborate?

8. Feb 23, 2008

### Cyrus

Sorry, Arildno already answered your question. I answered something you did not ask, so I deleted it. What I said is not wrong, its just not addressing your question. (Find out the answer to your question first, before moving on to what I said. I dont want to confuse you).