1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Buoyant forces

  1. Nov 25, 2008 #1
    I did an experiment where i measured the weight (in Newtons) of three objects on a spring scale. Then, i measured the weight (in Newtons) of the three objects on a spring scale while the objects were submerged underwater. How would i calculate the volume and buoyant force?
  2. jcsd
  3. Nov 25, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Please show your work.

    May we assume you weighed each of three objects dry (out of water) and wet (submerged)? Is there a difference? If so, what is the reason for the difference.

    When measuring submerged, did one measure the change in water level or volume?

    Does one know the density of the objects?
  4. Nov 25, 2008 #3
    Yes i measured the objects both dry and wet. Object one was 2.00 Newtons dry and 1.75 Newtons wet. Objects two was .57 Newtons dry and .45 Newtons wet. Object three was 2.00 Newtons dry and 1.75 Newtons wet.

    I do not know the density of any of the objects.
  5. Nov 25, 2008 #4
    I figured out the buoyant force is the difference in the weight of the objects from dry to wet. I also figured out the volume of the objects by using the formula Buoyant force = Density of the fluid times the volume of the fluid times the acceleration due to gravity.

    How would i start to calculate weight density and mass density of the three objects?
  6. Nov 25, 2008 #5
    The water that an object displaces is equal to the buoyancy force of that mass. So the weight difference can be used to determine the volume. For example the weight difference for the first object was 0.25 Newtons. 0.25 Newtons is 25.5 grams of water displaced or since the density of water is 1 gram per cc then that means you displace 25.5 cc of water. So object one's density is 2N/.0255L or 78.4 Newtons/ liter or 8 Kg/L. Did you know that you used the same figures for items one and three?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook