Interesting Question???

I was wondering--When you add live rock to a tank, does it add its dry weight to the total tank weight or its buoyant weight????

 

Is this a trick question? If it is live rock it shouldn't be dry.

It should add the buoyant weight to the tank. When you hold the rock under water it always feels lighter than outside the tank.

Dry base rock should start out with a lighter buoyant weight and then get heavier over time when water saturates all of the small pores.

 

Agreed. Live rock = wet rock.

 

hahah-by dry I meant its weight out of the tank--so it is the buoyant weight?

 

No. If you weigh the rock outside the tank, that is how much heavier the tank will be. Remember for every force there is an equal and opposite force. The buoyancy force on the rock is equal to the increase of the force of the water against the bottom of the tank.

The buoyancy force offsets itself and the rock still has the same gravitational pull (weight) regardless of being in water or not.

 

BINGO!!! k+

 

Yes! I knew 3 years of physics would come in useful some day. ;D

 

Thanks stevo---That makes sense!!!