Introduction
This paper examines the physical meaning of density in the context of immersion of various objects in water. It is known that some objects float, and others sink when submerged — the reason for this is the difference in density, or specific gravity. Specific gravity should be called the ratio of the density of a body to the density of the liquid in which that body is immersed. The paper first offers calculations for determining the densities of three different bodies, followed by answers to lab questions.
Data
Initially, for each of the three objects, their dimensions and masses were measured, which was used to calculate the densities. The table below shows the values of both measurements and calculations for the metal cylinder, wooden block, and irregularly shaped object. As you can see from the data in the table, the density of the metal cylinder is much higher than the density of the wooden block and the more so of the irregularly shaped object. Considering that all three objects were placed in water, it is obvious that the metal block appears to be more immersed in water than the other objects.
Result
From observation, we can see that density is a more descriptive variable than weight. Comparing weights alone between objects does not allow us to judge how they will behave when immersed in a liquid. Instead, it is worth using density as a descriptive variable – comparing densities allows us to determine that objects with higher densities will immerse more in the liquid than objects with lower densities. When a body is immersed in a liquid, a buoyant force acts on it: the greater the value of this force, the smaller the apparent mass of the body becomes. When a body is immersed in liquids other than water, there is also a change, because it depends on the difference in densities. Thus, the ultimate change in the true mass of the body will depend on the density of the liquid into which the body is immersed.
The same amount of iron and aluminum will visually look different when immersed in water because the density of iron is greater. Since the density of lead is greater than the density of aluminum, iron will lose less mass than aluminum.
When the finger is dipped into the liquid placed on the scale, the mass value will naturally increase. The point is that a pushing force will act on the finger, and some amount of water will be pushed out of the glass. At the same time, in order for the finger to maintain a stable position inside the beaker, there will be an inverse ejection force acting on the water. As this force is added, you can expect the mass on the scale to be slightly higher than the original mass before the finger was submerged.
When samples are immersed in liquids, their weight changes due to the pushing force; the explanation for this is the difference in densities. However, the density of air is significantly lower, so the change in the true mass of the sample will not be as great as it was with water. In reality, the change in true mass will occur, but it is unlikely that it will be a significant change. For example, a metal cylinder immersed in air does displace some of the air space, which in turn results in a pushing force of air. However, because of the small difference in density, the change will be almost imperceptible.
The fact that the Mendeleev-Clapeyron equation relates temperature and volume should be used to relate density and temperature. As temperature increases, volume naturally increases, with the most noticeable changes occurring for liquids and gases. As volume increases, the density of the body experiences a decrease. Consequently, we can conclude that as temperature increases, the density of bodies decreases.
Conclusion
To summarize, the physical meaning of densities is determined by the ability of bodies to push out when immersed in liquids. However, there are too many variables that affect the result of immersion or ejection: temperature, sample material, liquid density. The lab work demonstrates that the density of bodies can be measured directly.