Recent content by per persson

I don't understand how why the derivative is continuous. Clearly there is a surface charge and by gauss law we should have

Above is the pages of the problems. T is the force caused by a cable. I'm still lost on how to determine if there is reactive moment or not when there are more than two supports. If I understand your method right you find an axis where reactive forces of two supports do not cause a torque...

In the picture below consider the plane where T_z and T_y of T lie and the plane where A_x and A_y lie. They intersect in a line which is parallel to the x-axis. The force 300lb and A_z causes a torque around this axis but it does not prevent the rotation around it thus there is a reactive...

Are you saying given a set of forces how to find an axis where there is no torque about it? I would just check if the action of line of the forces pass through the axis or are parallel to the axis.

I'm thinking a disc centered at z=0 that lies on the xy-plane. The only forces that will not cause the disc to spin are those for which the action of line passes through the z-axis and those which are parallel to the z-axis. Correct? Edit: Sorry it should say how can I determine from a diagram...

In the book engineering mechanics statics and dynamics Hibbeler says:" It should be noted that the single bearing supports in items (5) and (7), the single pin (8), and the single hinge (9) are shown to resist both force and couple-moment components. If, however, these supports are used in...

In r<a the potential is V_o. I don't understand why in a<r<2a, V(r)=V_o-\int^r_a E*dl. I would write V(r)=\int^r_a E*dl+\int^2a_\infty E*dl I dont know how to write math symbols here but I wrote question here...

I remember yes. I think I understand moment better know. Consider a beam that is fixed to the wall. The gravitational force on the beam causes a moment and where it is fixed to the wall prevents the rotation of the beam thus in a free body diagram we draw a moment there. But if beam is fixed at...

So the hinges prevent each other from rotating. So when drawing a free body diagram I have to take into account all constraints. So for a case where there is a horizontal beam in 2d that is fixed into a wall at each end there is not moment at these points in the FBD. But if the beam instead is...

I think I got it.

Why are there no moments at hinges in the FBD?

But there is rotation around one axes the y axis. But no rotation about the x and z axes. Should there not be 2 moments M_z and M_x because of this?

it says that the door can rotate around the axis OA. How can I determine if it is a free hinge or not?

sorry I got confused it is not that picture it is this At O and A there are hinges but no moment