Air pressure on resting object

[XOT]

---

Members don't see this ad.

I am trying to make a link between Pascal's principle and an object resting on a table (if there is an actual connection?).

I understand that at the surface in a tank filled with fluid, this fluid can feel three forces:

1) force due to atmospheric pressure above the fluid pushing down
2) force due to weight of the fluid (similar to gravitational force)
3) force due to fluid below the liquid pushing up (similar to contact force)

Does an object at rest on a table also feel these three forces? I was under the assumption that there is only two forces on this object (similar to forces 2 and 3; contact and gravitational forces). Why is it never mentioned that there is a force due to atmospheric pressure on an object at rest on a table??

Thanks for the help.

 

[milski]

The contact between the object and the table is not really air-tight. As a result you have two forces - one from above and one from below. The latter is slightly larger (and the difference is what would account for buoyancy) but for typical objects at atmospheric pressure the difference is so small that it is normally neglected.

If you want to be absolutely precise, there are forces on the sides of the object too. For these it can be proven that when the forces from all directions are taken into account, they'll cancel each other.

 

[XOT]

Thanks for your input, milski- very much appreciated. I think it makes more sense now.