Does Density Affect Weight?

Hola folks! Here we are with another interesting topic for all of you science lovers.

Playing with balloons is one of the fondest memories of all of our childhood.

So tell me, if you fill a balloon with water and another balloon with air and throw them both in water, what would happen?

Obviously, the water-filled balloons will sink while the air-filled balloon will float.

So, why exactly did this happen? Let’s find out….

So, does density affect weight? Yes, density affects weight but, under specific conditions. The density of an object is directly proportional to its mass and inversely proportional to its volume. On the other hand, weight is directly proportional to mass and independent of volume. Therefore, the density of a substance increases with its weight, provided that the volume of the object remains constant.

In this article, I will focus on density, weight, mass, and volume. I will also cover their co-relation with each other. So, Stay connected.


What are Density and Weight?

Density is the measure of mass contained per unit volume of a material. It is denoted by the unit Kg/m3 or g/mm3.

The density of particular material remains the same, whatever be its shape or size. The formula for density is given below:

Density = Mass/Volume

Therefore, if the mass of an object is M and its height, length, and width measure L cm each, then the density of that object is given by M/L3.

Here, if we increase or decrease the measurements of this object, its volume would increase or decrease accordingly. Hence, the density would remain the same throughout the object.

The weight of a substance, on the other hand, is the measure of its mass under the influence of gravity. Hence, more the mass of an object more is its weight. Similarly, the weight of a substance also increases or decreases with a change in gravity.

For example, the weight of a substance would be more on the earth in comparison to the moon owing to the lower gravitation constant of the moon.

Weight = M * g

For a better understanding of both these concepts let us look at the diagrams below:

Density of Rubik

In the above picture, the density of the Rubik’s cube is the same as the density of one of its cubes separately, irrespective of the difference in size as the ratio of mass to volume remains constant.

However, the weight of the Rubik’s cube would definitely be more than the weight of its one small cube piece measured separately.

Now, look at the picture given below:

Density of Wood

It is clear from the above picture that even when both the logs are made of wood their weights are different owing to the difference in their mass. However, as both the logs are made of wood, the density would remain the same for both of them.

The following table differentiates between density and weight elaborately.

Density Weight
The density of an object is given by the mass contained per unit volume of an object. The formula for density is:

Density = Mass/Volume

Weight is the measure of the mass of an object under the influence of gravitation force. It is given by the formula:

Weight = Mass X Gravitation

It is an intensive physical property of an object. It is an extensive property of an object.
The density of an object changes under the influence of temperature and pressure. The weight of an object changes with variation of mass and force of gravity.
The unit of density is given by Kg/ cubic meter cube or gram per cubic milliliter. The unit of weight is Kilogram or Newton.
Density varies in terms of four extensive properties viz. length, width, height, and mass. Weight varies only under the influence of two properties viz. mass and gravity.


What does Less Dense Mean?

To understand this look at the following pictures:

Less Dense Forest

More Dense Forest

Out of Figure 1 and Figure 2 given above which one has more density of tree?

Obviously, it is Figure 2, as it has more trees in the same area. Hence, the forest shown in Figure 2 is denser, while the forest in Figure 1 is less dense.

Similarly, in terms of matter, if a substance contains more molecules or atoms in the same capacity then it is denser while the other substance will be less dense. You can compare the atoms or molecules to the trees given in the above pictures. More trees mean more density.

Now, look at the pictures below and tell me if the red and blue balls symbolize atoms then, which of the following substance is less dense?

Atoms Density

You are right. Substance 2 is denser than substance 1.


Does More Density Mean More Weight?

Up till now, you have understood that more density means more mass per unit volume. This means that an object with a higher density has more mass in the same volume in comparison to an object with lesser density.

Hence, more density does not imply more weight.

Let’s take an example, if you have a rock in hand and a big water body in front of you which one do you think has more mass?

You know the answer, it is the water body. It is way too bigger than the rock but, it also occupies much more space. So, what would happen if you throw that stone in water? Obviously, it would sink.

But, why did this happen? After all the big water body has a lot more weight than the small stone in your hand. It is because the density of stone is way more than the water as the large mass of water is scattered in large volumes.


How Does Density Impact Weight?

Density is the measure of how tightly the molecules or atoms are packed in an object. The closer the molecules are arranged or larger numbers of molecules indicate higher density.

Hence, solids are the densest of all the states of matter while gases are the least dense of all.

As discussed in the earlier sections, the weight of an object is directly proportional to its mass indicating that higher the mass of an object higher is its weight.

The density of an object is also directly proportional to its mass but is inversely proportional to volume.

Therefore, even if the mass of an object is high, it might have a lower density owing to a larger volume.

Drawing the relation between weight and density:

Weight, W = Mg; Implying that, M =W/g

Density, D = M/V; Implying that, M = DV

Putting these values in one equation, W/g = DV

Therefore, Density and Weight are directly proportional to each other. But, as density is also inversely proportional to volume, the density of an object would increase in the same proportion as weight till its volume remains constant.

Check out the video attached explaining the density.



Relation of Density with Temperature and Pressure

The two major factors that affect the density are:

• Temperature

An increase in temperature results in the increase in kinetic energy of the particles constituting an object. Due to this increase in kinetic energy, the particles start vibrating at higher speeds owing to which the number of collisions also increases.

As the number of collisions increases the particles get pushed away from each other, and hence, the density of the object decreases.

Therefore, density is inversely proportional to temperature. I have also written a specific article on it.

Check out Does Density changes with temperature.

The density variation with change in temperature for water is shown in the graph below:


As per the graph, the maximum density of water is reached at 0°C when it is in the form of ice. Further, as the temperature keeps increasing, the density keeps declining.

• Pressure

Unlike temperature, pressure is directly proportional to density. As the pressure increases the particles inside a substance get pushed towards each other.

Therefore, the volume keeps decreasing, and ultimately, more particles are accommodated in lesser space. This means that the density of the substance increases with the pressure.

The pressure versus Density graph is given below:

Calculated relationship between density and pressure, using REFPROP. | Download Scientific Diagram



Question: Does the shape of an object affect its density?

Answer: No. The density of an object will remain the same when the shape is changed. You can understand this by recalling that the formula for calculating the volume of different objects is different. So ultimately, the volume will remain the same and hence, density unaffected.

Question: Does density depends upon the amount or size of an object?

Answer: No. Density is an intensive property which means it is unaffected by any change in the size or amount of an object.

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The density of an object is directly proportional to its weight provided that the volume of the object remains constant.

Density is measured using the formula, D = M/V, where, M is the mass of the object and V is the volume.

The weight of an object is measured by the formula, W = Mg, where M is the mass of the object, and g is the acceleration due to gravity.

Happy learning!!

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