If three objects all float on top of water, what must be true about the objects?
A. They must have the same mass, even if their volumes are different.
B. They all have densities less than the density of water.
C. They must have the same volume, even if their masses are different.
D. They all have densities greater than the density of water.
The correct answer and explanation is:
The correct answer is B. They all have densities less than the density of water.
Explanation: When an object floats on water, it means the object is less dense than the water. The principle behind this is based on Archimedes’ principle, which states that a floating object displaces a volume of water whose weight is equal to the weight of the object. For an object to float, the buoyant force acting on it (which is equal to the weight of the displaced water) must be equal to the weight of the object.
For this to happen, the density of the object must be less than the density of the fluid (in this case, water). Water has a density of about 1 gram per cubic centimeter (g/cm³). If the density of the object is greater than the density of water, it will sink because it will not displace enough water to balance its weight. If the object’s density is less than that of water, it will displace enough water to support its weight, causing it to float.
The other options do not correctly explain why the objects float:
- A. Objects floating on water do not need to have the same mass, even if their volumes are different. Mass is not the determining factor for flotation; rather, it is the object’s density in relation to the fluid’s density.
- C. Objects floating on water do not need to have the same volume. Different volumes can have different masses but can still float if their densities are less than that of water.
- D. If an object has a density greater than that of water, it will sink, not float.
In conclusion, for an object to float on water, its density must be less than the density of water, which is why option B is the correct answer.