# Contact forces

1. Sep 11, 2009

### dorian_stokes

I've looked everywhere to find how do you calculate contact forces, like if you were pushing boxes. Don't want the answer just need to know how to do the calculations.

2. Sep 12, 2009

### Staff: Mentor

It depends on the problem, but you'll be using Newton's laws. Post a specific problem in the Intro Physics section (showing your work) and you'll get plenty of specific advice.

3. Sep 14, 2009

### dorian_stokes

contact forces with coefficient of friction

If you have two boxes being pushed where both have different masses and both boxes have a coefficient kinetic friction how do you calculate the normal force between the two?

4. Sep 14, 2009

### Staff: Mentor

Dorian, as Doc says, you should post your specific schoolwork question in the Introductory Physics sub-form in the Homework Help section of the PF, and show your attempt at a solution. You should get good advice in that forum.

5. Sep 14, 2009

### dorian_stokes

I'm trying not to use the exact question. Here's a revised one. Lets' say that a person is moving two boxes. M1 is 14 kg and M2 is 10 kg and the coefficients of kinetic fricton between both the boxes and the floor is .10. What is the Normal force between the two boxes? Please can you explain this in as simple terms as possible?

6. Sep 14, 2009

### Staff: Mentor

Draw a diagram....see where the force vectors of the weight overlap and don't overlap...

7. Sep 14, 2009

### Staff: Mentor

Thread moved to Homework Help. And why would you be trying to not use the actual question? A bit worried that your professor and fellow students can use Google?...

8. Sep 15, 2009

### Staff: Mentor

What do you think it would be? If a box with mass m is sitting on a horizontal surface, what do you think the normal force is between the box and the surface?

Hint: Analyze the vertical forces acting on the box, one of which is the normal force.

The same thinking is needed when you have two boxes.