Name:____________________
Density, Buoyancy, and Force Diagrams PhET Lab (rvsd 2/2011)
Introduction
You’ve heard that oil floats on water. You also know that ice cubes normally float in a glass of water. Why? What
causes some things to float in water (corks, ice, dogs) and some to sink in water (rocks, metal spoons, mobsters)?
Density is often described as the amount of mass crammed into a volume, and is illustrated by the formula shown
below. The units for density are expressed g/cm3, g/mL, kg/m3, and kg/L. In this simulation, we will use kg/L.
Water’s density is 1.00 kg/L.
Important Formulas:
Procedure: PhET Simulations Play With Sims Physics Density
•Take a few minutes and familiarize yourself with the simulation before moving on.
Free Body Diagrams for Floating Objects:
•Grab the various blocks, lift them over the water and drop into the water a few times.
•In the boxes at the right, draw free body diagrams for a falling block, block under water, and a floating wood
block.
•When is the block accelerating? ________________&________________________
•What should be the net force in the vertical direction when the block is floating? _____
The %-Density Ratio Trick
•
Estimate the percentage of the wood, ice, and Styrofoam block that is under water while those blocks are floating.
Remember: the density of water is 1.00 kg/L
% Wood under water % Ice under water % Styrofoam under water
Density of Wood Density of Ice Density of Styrofoam
•Compare your estimations to the densities shown on the chart . Place those densities in the chart
above.
•Create a formula to show how much of a floating object would be submerged in any fluid.
% under =
____________
_
