Motion of an object submerged in water.

[aero&astro]

ignoring drag, how could you describe the motion of a cylindrical object in water, if the upwards buoyancy force is given by a certain equation? (B = [1020+0.25z]Volumexgravity)

I'm not sure if its just Fup = Fdown where Fdown is the weight and Fup is the buoyancy. However it can't be that or else the cylinder wouldn't have motion it would be stationary, wouldn't it?

 

[tiny-tim]

hi aero&astro!

(try using the X₂ icon just above the Reply box )

I'm not sure if its just Fup = Fdown where Fdown is the weight and Fup is the buoyancy. However it can't be that or else the cylinder wouldn't have motion it would be stationary, wouldn't it?

no, F_up = F_down would be the equilibrium equation

you need (as usual) good ol' Newton's second law …

F_up - F_down = ma

 

[aero&astro]

why is it Fup - Fdown and not Fdown - Fup?

 

[Metaleer]

Because tiny-tim assumed a reference frame where "up" points to positive values, and "down" points to negative values.

 

[tiny-tim]

Y_up!

 

[aero&astro]

thanks a lot guys, this really helped.