Three small objects are released from rest at the surface of a large, open container of fresh water (density 1.0×103kgm−3). Each object has the same volume.
• A wooden cube whose average density is 7.0×102kgm−3
• A sealed, hollow glass bulb that contains a partial vacuum, so its average density is 9.8×102kgm−3
• A solid steel sphere whose density is 7.8×103kgm−3
After several minutes, the water in the container is completely replaced by glycerin (density 1.3×103kgm−3) without disturbing the positions of the objects.
(a) For each object in fresh water, indicate whether it ultimately rises above the surface, remains partially submerged, or sinks to the bottom.
(b) For one of the objects that floats, qualitatively compare the upward force exerted by the water to the weight of the object and explain how this comparison determines the observed motion.
(c) After the water is replaced by glycerin, predict the new vertical positions of all three objects. State explicitly whether any object’s behavior changes and why.
(d) Consider only the steel sphere in glycerin. Describe all forces acting on the sphere and state whether a net force is present. Justify your answer using appropriate comparisons of physical quantities.