# Free body diagrams for forces on a block

1. Feb 7, 2005

### wajhea

Hi all,

For an online physics assignment I have a question about a block resting on a slope. The question asks what forces are acting on the block.. and I was thinking normal and weight force? But it turned out to be incorrect...

list of possibilities to choose from
weight
kinetic friction
static friction
force of push
normal force

2. Feb 7, 2005

### Staff: Mentor

If the block is resting on the slope, what does that tell you?

3. Feb 7, 2005

### wajhea

Does it mean that there are no forces acting on it? I don't know, I don't get this stuff.

4. Feb 7, 2005

### wajhea

or static friction maybe?

5. Feb 7, 2005

### Staff: Mentor

It means that the net force on the object is zero. So what additional force is needed to balance the component of the weight acting down the slope?

6. Feb 7, 2005

### wajhea

normal force?

7. Feb 7, 2005

### Staff: Mentor

No. The normal force is perpendicular to the surface of the slope, so it cannot act to balance out a force parallel to the surface.

8. Feb 7, 2005

### wajhea

So could the static force balance out the forces?

9. Feb 7, 2005

### Staff: Mentor

Absolutely! If there were no friction, the object would slide down the slope.

10. Feb 7, 2005

### wajhea

Thanks...

as my answer I put down weight and static friction, but turns out that was wrong because the answer also includes normal force. Oh well.....

11. Feb 7, 2005

### Staff: Mentor

Yes. Three forces act on the object.