Buoyant Force in High vs Low Density Liquids: Homework Statement & Solution

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
36 replies · 4K views
haruspex said:
Yes, that would generally be true.
So, the reason that the object is less stable in more dense water is because when the object float higher in liquid, it has more tendency to turn over?
 
Physics news on Phys.org
chetzread said:
So, the reason that the object is less stable in more dense water is because when the object float higher in liquid, it has more tendency to turn over?
Yes. But as I posted, that is only the general trend. There may be exceptions according to shape.
 
  • Like
Likes   Reactions: Simon Bridge and chetzread
haruspex said:
Yes. But as I posted, that is only the general trend. There may be exceptions according to shape.
Exception according to shape? Can you explain further?
 
The trick is to realize what gives rise to the stability.
To do that, draw the same shape in two different liquids, as per my example to start with, then do another sketch with them a bit tilted over.
Look to see where the forces act (hint: pressure is perpendicular to the surface, and the pressure at the sides is also important.)

Do you understand where the buoyancy force comes from in the first place?

(I know I said "tomorrow but I have insomnia - and I saw post #25 before post #24 for some reason.)
 
  • Like
Likes   Reactions: chetzread
Simon Bridge said:
The trick is to realize what gives rise to the stability.
To do that, draw the same shape in two different liquids, as per my example to start with, then do another sketch with them a bit tilted over.

Look to see where the forces act (hint: pressure is perpendicular to the surface, and the pressure at the sides is also important.)

Do you understand where the buoyancy force comes from in the first place?

(I know I said "tomorrow but I have insomnia - and I saw post #25 before post #24 for some reason.)
Here it is, so what are you trying to say?
 

Attachments

  • IMG_20161002_225508.jpg
    IMG_20161002_225508.jpg
    16.9 KB · Views: 455
is there anything to do with the metacentric height , buoyant point in this question ?
 
chetzread said:
is there anything to do with the metacentric height , buoyant point in this question ?
Not specifically. I just wanted to alert you to the fact that the topic is subtler than may appear, that it might not actually be true that the object would always be more stable in the lighter fluid, and that even if it is a rigorous proof would not be easy.