If three objects all float on top of water, what must be true about the objects?
A. They all have densities less than the density of water.
B. They all have densities greater than the density of water.
C. They must have the same volume, even if their masses are different.
D. They must have the same mass, even if their volumes are different.
The correct answer and explanation is:
The correct answer is A. They all have densities less than the density of water.
Explanation:
For an object to float on water, its density must be less than that of water. The principle governing this is Archimedes’ principle, which states that an object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced. For an object to float, the buoyant force must be equal to the weight of the object. This happens when the object’s density is less than that of the fluid it is placed in (in this case, water).
Water has a density of about 1 g/cm³ at 4°C. If an object is floating on top of the water, it means it is displacing a volume of water equal to its weight. For this to occur, the object’s density must be lower than that of water, as a denser object would sink due to the inability of the buoyant force to overcome its weight.
On the other hand, if an object has a density greater than water’s, it will sink. Objects that float are generally less dense than the fluid they are in, which explains why materials like wood, ice, and certain plastics float on water.
Options B, C, and D are incorrect for the following reasons:
- Option B: If the objects had densities greater than that of water, they would not float.
- Option C: The objects do not need to have the same volume to float; they can have different volumes as long as their densities are less than that of water.
- Option D: The objects do not need to have the same mass to float; they can have different masses but must have densities less than water to float.