# Homework help (Force of friction)

1. Feb 11, 2012

### -Physician

1. The problem statement, all variables and given/known data
We have a body with force $F=10N$. Now we know Force of friction makes the body not move if the Force of friction $F_f$ is higher than the normal force $F_n$, so what force of friction do we have to depress to make the body move

2. The attempt at a solution
We know that the force of friction $F_f$ has to be lower or equal to normal force $F_n$, so the solution would be:

$F_f ≤ 10N$

Am I right? Thanks!

2. Feb 11, 2012

### PeterO

Where is this body? is it being pinned to a vertical wall with a horizontal force or are you trying to push it across a surface?

3. Feb 12, 2012

### -Physician

4. Feb 12, 2012

### SammyS

Staff Emeritus
In general the normal force is perpendicular to the surface, and the force of friction is parallel to the surface, so this question appears to make no sense!

What is the context of this question?

Where did you find it?

Who gave it to you?

Where did that person find it?

5. Feb 12, 2012

### -Physician

It's my teacher's homework ..., she found it from the book, and the task says:

The body has force $F=10N$. What force of friction $F_f$ do we have to depress to make the body move. Remind:
The force of friction $F_f$ has to be lower or equal to normal force $F_n$, so the body can move.

This is the exact text that is written on the book.

6. Feb 12, 2012

### PeterO

Well that might be what is written, but it still makes no sense at all.

Breaking down what you have written:

"The body has force $F=10N$" .
Now if the body had a weight of 10N it would have more meaning.

"What force of friction do we have to depress ... "
If that had read "What force of friction do we have to oppose ... " we would be part way to a logical situation.

"The force of friction $F_f$ has to be lower or equal to normal force $F_n$, so the body can move".

Not quite sure what that might mean????

7. Feb 13, 2012

### -Physician

That's what is written on book, maybe they're technical mistakes?