This is a question from [url=http://www.physics.umd.edu/lecdem/outreach/QOTW/arch1/q003.htm]The Physics Question of the Week[/url] at Univ. of Mrayland.
A ball floats on water, as seen in the photograph below, but will sink when put into mineral spirits. The water is dyed green with food coloring to distinguish it from the clear mineral spirits. Note how far the floating ball sinks into the water.
[img]http://www.phy.ntnu.edu.tw/demolab/phpBB/2/33_f2-26a.jpg[/img]
When the mineral spirits is poured slowly onto the top of the water, it will remain on top because the two fluids are immiscible.
If the mineral spirits is poured slowly on top of the water while the ball is floating on the water, what will happen to the level at which the ball floats?
* (a) The ball will float lower into the water.
* (b) The ball will float higher out of the water.
* (c) The ball will float at the same level with respect to the surface of the water after the mineral spirits are poured on top of the water.
The following simulation will let you play with the above experiment with java applet.
An object with density d2 is floating on a liquid with density d1. (d1>d2)
You can drag h3 to add another liquid with density d3 to find out what will happened to the object d2.
You can change density for d1,d2,d3 and height for those two liquid.
Click showp to find out how the pressure changed.
I hope you can enjoy playing with this applet and learn more about buoyancy force (liquid pressure as well) ::)

Virtual Physics laboratory Original URL

Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.