Question about bouyancy... Looking for a hint

Forums › Science

Anonymous
10 Feb 2006 20:40:23 UTC
Topic 13268
(moderation:
    )

    Quote:
    Equilibrium is what you are after. Volume of mercury displaced * density of mercury = iron sphere mass. When you add water, what changes?

    I think this assumes the density of air is zero, which is a good approximation.
    Volume of mercury displaced * density of mercury + Volume of air displaced * density of air = iron sphere mass.

    This should be a good hint.

    David Hammer
    David Hammer
    Joined: 15 Oct 04
    Posts: 144
    Credit: 82,938
    RAC: 503

    Question about bouyancy... Looking for a hint

    11 Feb 2006 8:20:33 UTC
    Message 2790
    (moderation:
      )

      Here is a thought experiment that may make the solution clearer.

      If you weighed an iron ball in a vacuum would it weigh the same as it weighs at the bottom of a swimming pool? By weight I mean the force the ball would apply to a scale.

      In a vacuum the iron ball would weigh
      [mass of iron * acceleration due to gravity]
      Gravity pulls the ball down and there is no force pushing up.

      On the other hand at the bottom of a pool it would weigh
      [mass of iron * acceleration due to gravity - mass of displaced water * acceleration due to gravity]
      Gravity pulls the ball down but there is now a buoyancy force pushing up on the ball.

      Would the iron ball need to sink as far into mercury to support its weight at the bottom of a swimming pool as it would in a vacuum?

      edit to improve clarity ???

      Comment viewing options

      Select your preferred way to display the comments and click "Save settings" to activate your changes.

      Forums › Science