How to Calculate the Force Needed to Move a Roller Over an Obstacle?

[John O' Meara]

A roller whose diameter is 1.0m weighs 360N. What horizontal force is necessary to pull the roller over a brick 0.1m high, when the force is applied (a) at the center, (b) at the top of the roller.
I need a diagram showing the forces acting at the point of contact between the roller and the brick, please? I only know how to use MS word which has no drawing tool in it.

 

[radou]

What exactly do you mean when you say 'a roller'? Could you draw a sketch of the problem with paintbrush and post the image?

 

[Astronuc]

I believe 'roller' means cylinder (circular cross-section).

The roller has radius 0.5 m, since the diameter = height = 1.0 m.

It might be easier to draw triangles.

Word does have drawing tool. If one doesn't see the drawing toolbar, go to View - Toolbars - select Drawing, and the drawing toolbar should be activated. If one doesn't have it installed, then install it from the CD, assuming one has MS Office or Word CD.

 

[John O' Meara]

Yes a roller means a cylinder. My attempt at drawing a cylinder in contact with a brick can be classed a failure, I wanted to show the lines of action of the forces acting on the brick due to the roller( as I see them) but the drawing got too messy. I have to figure out how to group figures like circles and lines to make a roller e.t.c.

 

[Astronuc]

Perhaps it would be better to simply draw the profile (2D) rather than perspective (3D). One can assume constant or uniform cross-section.

Draw a circle and place a box, with the corner in contact with the circumference. The bottom of the circle (OD = 1 m) and the base of the box (height = 0.1 m, or 0.1 of circle diameter) should be tangent.

Then draw the lines from the contact point of the box to the center of mass and the point of force application. Then use moments to determine the force necessary to lift the roller.