# New to Physics Forum and would like some help with concepts

1. Oct 12, 2011

### seekheart

Hi everyone,

I'm having some issues understanding how to approach (conceptually) a problem
where there is a box with a ramp with static friction. The scenarios that are problematic to me
are when you are pushing with a force horizontally and perpendicular to the surface.
It's not a hw problem so it's why I thought it would be appropriate here.

Thanks everyone

2. Oct 12, 2011

### ZapperZ

Staff Emeritus
This is very vague. You described the scenario, but did not describe what and where exactly you are having such a problem. What exactly is the issue here?

You may end up needing to go to the HW/Courswork forum, and present a typical HW question that you got stuck in.

Zz.

3. Oct 12, 2011

### seekheart

My issue is just how to do this type of problem when you want to find the force applied on the block.

4. Oct 12, 2011

### johng23

Draw a free body diagram, figure out the forces acting on the body, use Newton's laws.

5. Oct 12, 2011

### Trevormbarker

You may find it usefull to break your forces into componets that are perpendicular and parrallel to the surface of the ramp. ie for the force of gravity use mgsin(theta) where theta is the angle of the ramp

6. Oct 13, 2011

### Redbelly98

Staff Emeritus
As johng23 said, you need to be able to draw a free body diagram showing the forces. That's Step 1 in solving most of these problems. Make sure you account for all of the forces that are present (gravitational, normal force, friction, rope tension, or any applied forces).

Step 2 would be to set up the F=ma equations. Decide on directions for x and y -- usually x is taken to be along the surface that a given object is resting on or moving along. Then you can write up to two equations for each object in the problem:
ƩFx = m ax
ƩFy = m ay
Most forces will be in either the x or y direction. For forces acting at an angle, you'll need to write the force in terms of it's x and y components.

You'll also need to figure out -- usually from the wording of problem statement -- whether you can set ax or ay to zero or not.

Step 3, after you set up the F=ma equations, is to work through the algebra and solve the problem.

EDIT:
A possible complication happens when there is more than one object in the problem. There is usually some kind of relation between the accelerations of the two -- or possibly more -- objects. Objects that move together have the same acceleration. It's also fairly common, in a certain type of pulley arrangement, that one object has twice the acceleration of another. You'll need to figure out if that is the case.

Last edited: Oct 13, 2011
7. Oct 14, 2011

### jetwaterluffy

First find the components of the forces perpendicular and parallel to the plane. Do this using trigonometry, with the force as the hypotenuse of the triangle. If you want the friction, F=μR. μ is the friction coefficient between the surfaces, which is usually between 0.05 and 1, depending on how slippery the surface is. The reaction force should be equal to the component of weight perpendicular to gravity.