We need to understand the formula correctly and pay attention to the conditions and the special meaning expressed by each physical quantity.
From a mathematical point of view, there are three situations (judging right or wrong): when 1. ρ is fixed, and m is proportional to v; 2. When m is constant, ρ is inversely proportional to V; 3. When V is constant, ρ is proportional to M. Combining with the physical meaning, only (1) is correct in the three cases, while (2) and (3) are all wrong. Because the density of the same substance is constant and does not change with the change of volume and mass, we can't understand the physical formula without physical facts, nor can we simply understand the relationship between the quantities in the physical formula from a mathematical point of view.
Density is a measure of mass in a specific volume. Density is defined as the mass of an object divided by its volume. Density formula is widely used in practical application.
Can be used to identify substances: such as whether your gold jewelry is pure gold, what crops are suitable for planting in rural farmland, seed selection and so on.
Used to measure volume. For example, the decoration needs thousands of meters of wires, and it will take a long time to measure with a ruler, but it will be solved quickly with a scale.
Used to measure quality: for example, buy a few kilograms of bulk wine, gasoline, etc. We can check the volume and the corresponding density value to determine whether there is a shortage of two pounds.