Final answer:
To determine which object will float in water, we need to consider the object's density related to the density of water. An object with a density less than water will float, while the denser objects will sink. This is explained by Archimedes' principle, which connects buoyancy to the weight of the displaced fluid.
Step-by-step explanation:
Objects that are less dense than water float, while denser objects will sink. The density of water is a standard 1000 kg/m³. For example, oil is less dense than water and will float on top of it. On the contrary, most metals are denser than water, which leads them to sink. The principle behind this is closely related to Archimedes' principle, which states that the buoyant force on an object in fluid is equal to the weight of the fluid displaced by the object.
Considering a practical scenario, let's take a cube of polystyrene measuring 10 cm on each side. If 90% of the polystyrene is floating above the surface, implying that only 10% of the volume of the polystyrene is displacing water, we can calculate its density. To do this, we find the volume of the polystyrene submerged in water (which is 10% of the entire volume), calculate the mass of water equivalent to that volume (since the density of water is 1000 kg/m³), and then use this mass to determine the density of the polystyrene.
When additional weight is added onto the polystyrene block, such as a 0.5 kg mass, the percentage of the polystyrene that remains above water will decrease because the overall density of the polystyrene-mass system has increased, causing it to displace more water to balance the additional weight, according to Archimedes' principle.