密度

Why is a ballon filled with water heavier than a balloon filled with air? Why does filling up a bag with books make it heavier than filling it up with clothes?

To deal with this, physicists have made up the term density. Density is a property of a material, independent of its volume or mass, that is higher if and only if an equivalent volume has a higher mass.

$Density = \frac{Mass}{Volume}$

Density was actually discovered by Archimedes. Most people know the story about how he realized the concept of Density in his bathtub, and so ran onto the streets (immediately) shouting "Eureka".

The formula for density can be used to solve many real-world problems and applications. The concept is what makes it possible to differentiate between real gold and pyrite, fool's gold. It also allows for the understanding of Bernoulli's principle, a complex application of Density to understand the mechanical movements of a fluid. It even accounts for how such large boat's float, why oil simply refuses to mix with water, and also even for airplane movement.

What is density?

It is one of the more fundamental concepts of physics. It doesn’t include only physics but also our day to day life. So, let’s talk about it.

Suppose we have 1 kg iron. And we also have 1 kg cotton. Now if I ask to you which objects are more massive? Many of us can do the common mistake, that you can say the iron is more massive than cotton. But it is clearly wrong. Because 1kg cotton and 1 kg iron are same in mass. We know that the unit of mass is ‘kg’. Here we take 1kg cotton and 1kg iron, so they are same in mass, because both of them sustain the same mass and that is 1kg. Okay?

Now I have one another question to you which things allure you to choose the wrong answer in above case. Within a word the answer is ‘Density’.

If you take same volume of cotton and iron then you can realize that the mass of iron is more than the cotton. It indicates the feelings of density. Now we are able to define the conception of density.

‘’The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho)’’ – from Wikipedia

By using the unitary method we can emerge an equation for density.

Suppose I have an object which has a definite mass – ‘m’ and a definite volume ‘V’

Now we want to get the density of this object.

So let’s play with unitary method-

We get the mass ‘m’ for the volume of ‘V’

So, for 1 unit volume we get the mass - m/V

We know that density of an object is its mass per unit volume. So the density of my object is- ρ= m/V

ρ= m/V, actually it is true for the density of every object

Density is a characteristic property of a substance. The density of a substance is the relationship between the mass of the substance and how much space it takes up (volume). The mass of atoms, their size, and how they are arranged determine the density of a substance. Density equals the mass of the substance divided by its volume; D = m/v. Objects with the same volume but different mass have different densities.