Forces involved in strapping something down

Say I have a hollow cylinder and I wanted to strap it down to the bed of a truck. I would tension the strap on one end, and it would exert a force on the cylinder. My intuition tells me that the strap would crush the hollow cylinder down toward the truck bed, but when I think about it, there are inward forces perpendicular to the truck bed caused by the straps on the cylinder as well. Is this correct thinking, or are all of the forces only vertical?

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Do you mean inward forces parallel to the truck bed? –  Wouter Jan 15 '13 at 1:59
I have removed the tensors tag, which refers to mathematical objects, not the ones you use to tighten a strap! –  Jaime Jan 15 '13 at 4:16

If you neglect friction, the strap presses on the cylinder, and exerts a force perpendicular to the contact surface. So the infinitesimal length of strap sitting on the highest point of the cylinder exerts force downward, but at any other point, there will be a horizontal component as well. If the configuration of your strap is symmetrical, any horizontal force exerted on one side of the cylinder will be compensated by an equal, opposite force exerted on the symmetrical side.

So the overall force exerted on the cylinder has no horizontal component, only vertical, and equal to $2T \sin \alpha$, where $T$ is the tension of the strap, and $\alpha$ the angle the ends of the strap make with the horizontal. This is also the reaction that the truck bed will exert on the cylinder from below.

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