Re: [Phys-l] buoyancy on a submerged pole

[John Mallinckrodt <ajm@csupomona.edu>]

Chuck Britton wrote:

> I THINK that my hypothesis can be restated as saying that an object 
> submerged in a fluid will experience an UPWARD force that is equal to 
> the weight of the fluid displaced.

This sounds a lot like the misconception many students have that IF an object is moving along a circular path THEN it is subject to a "centripetal force" equal to mv^2/r .  That "centripetal force" must, therefore, be added to any other forces that might act on the object.

To avoid making that mistake, it's worth reminding them (and ourselves!) that forces always have local "agents" either in the form of "fields" (e.g., gravitational or electromagnetic) or "via direct contact."  If you can't identify the agent, the force does not exist.

John Mallinckrodt
Cal Poly Pomona