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Is Density A Physical Property: Why, How And Facts

January 20, 2024March 7, 2022 by AKSHITA MAPARI

The density is the matter depends upon the number of atoms or molecules occupying the unit volume of the mass. In this article, we shall discuss how is density a physical property.

The density is a physical property of the object and is defined as the ratio of a mass of the matter constituting the unit volume of the object and is given by the relation:-

ϱ =m/v

Where ϱ denotes the density of the matter

m is the mass and

v is a volume of the matter

How is Density a Physical Property?

The smaller the volume and greater the mass of the object, the density of the object will be more.

The density of the object depends upon the mass and the volumes, which are the physical properties of the object; consequently, the density is a physical property.

The density of the object signifies the impenetrability of the molecules, such a tightly compact mass. The void spaces between the molecules keep some gaps between the molecules. If the object is suspended to the heat, the bonds between the molecules take this energy. When the energy acquired by the molecules is high enough, the bonds between the molecules break, and the distance between the separation of the two molecules increases. And hence the solid turns to liquid and liquid turns to gaseous form.

The density of the solid is more as compared to the liquid and the density of the liquid is more than that of gas. Likewise, the volume acquired by the same number of molecules in solid is less compared to the liquid and the molecules of a gas are suspended to a greater distance than that of the liquid.

Is Density Change a Physical Property?

The density of the object changes if the mass or volume of the object varies due to some external effects.

The variation due to the density is obviously the inevitable of the change in the volume or mass of the object; hence density change is also a physical property that is a cause for the physical change.

If you consider a simple example of the air conditioners there is basically the change in the phase from gaseous to liquid and then liquid state to back into the gaseous form. The compressor is used to compress the gas to form a liquid which then passes through a coil and gets cool and released out.

How is Density Change a Physical Property?

The rise in temperature breaks the molecular bonds between the atoms resulting in increasing the space and hence the volume of the matter.

As the volume of the object increases, the matter occupying per unit volume of the object will decrease, thus the density of the object will decrease, which is a physical change.

The density of the object will increase if the object is compressed. Upon compression, the vacant spaces between the object will be filled. This will reduce the gap between the molecules comprising the matter, and thus the mass per unit volume of the matter will be more and therefore the density of the object will increase on compressing. In short, we can say that the rise in pressure on the object will ascend the density of the object.

is density a physical property — **Gas Compressor;**
**Image Credit: Pixabay**

If the pressure on the object is lowered, then the molecules will spread in the surrounding region, which will result in a decrease in density. In this case, the change in the volume of the object will result in a variation in the density.

What is a density change of gas with increasing temperature if the volume changes from V₁ to V₂?

The initial volume of the object is V₁ and the final volume of the object is V₂.

The density of the object is the ratio of m/v, hence the change in density is

The mass of the object remains the same while only the volume of the object extends from V₁ to V₂.

What is a density change of a container if some molecules of a gas escape from the container?

The molecules of a gas escape from the container; hence there is a decrease in the mass of the container.

While the volume of the container remains the same and gas molecules can easily spread all around the container. Therefore the change in the density is due to the decrease in the mass of the gas in a container, given by,

Where Δ m=m₂-m₁

Frequently Asked Questions

A gas of volume 0.3m³ is compressed at a pressure of 1.2atm. The gas is converted into the liquid upon compression giving a final volume of 0.08m³. What is a density change of a matter having a mass of 25 grams?

Given: m=25 grams=0.025kg

V₁=0.3m³

V₂=0.08m³

We have,

gif.latex?%3D0.025%5Ctimes%20%5Cleft%20%28%20%5Cfrac%7B1%7D%7B0.08%7D %5Cfrac%7B1%7D%7B0

gif.latex?%3D0.025%5Ctimes%20%5Cleft%20%28%20%5Cfrac%7B0.3 0.08%7D%7B0.3%5Ctimes%200

This is the rendered form of the equation. You can not edit this directly. Right click will give you the option to save the image, and in most browsers you can drag the image onto your desktop or another program.

The change in the density of the matter is 0.23 kg/m3.

Four ice cubes of dimensions 3cm ×4cm ×5cm and mass 55.2 grams each are kept in a cylindrical tray of diameter 8 cm and height 10cm. The ice cubes are completely melted to form water and the cylinder is filled to the height of 4cm. What is the density change of ice to water?

The volume of the ice cube is

V=l x b x h

=3 x 4 x 5

=60cm³

Hence, the volume of 4 ice cubes is

V=4 x 60=240 cm³

Density of ice is

= 4 x 55.2/240

=0.92 g/cm³

Volume of water in the cylindrical container is

V_c=πr²h

=3.14 x (4)² x 4

=200.96 cm³

We know that the density of water is 1 g/cm3, hence the mass of the water is

M=ϱ_water V

M=1 x 200.96=200.96 grams

The change in the density is

Δϱ =ϱ_water-ϱ_ice

=1-0.92=0.08 g/cm³

Why does the density of ice is lighter being in a solid state as compared to the water?

The solid is usually denser than the liquid, but so is not true in the case of water and ice.

The bonds formed between the hydrogen and oxygen atoms are in a tetrahydrate structure. The orientation of bonds between the molecules in ice makes a void thus decreasing the density of the water in the solid form.

How does the temperature affect the density of the object?

The temperature may increase or decrease the density of the object.

The rise in temperature provides the heat energy to the mass that essentially breaks the bonds between the molecules and the phase change occurs, reducing the density of the object. While lowering the temperature increases the density of the object.

How does the pressure affect the density of the object?

The rise in pressure increases the density of the object.

On imposing the pressure on the object, the molecules in the object exert a force that basically brings them closer to each other forming a compact structure; this increases the number of molecules per unit volume of the object.

Also Read:

When Does A Physical Change Occur: Detailed Analysis

January 20, 2024November 8, 2021 by Rabiya Khalid

The changes happening around us are either chemical or physical changes. Let’s have knowledge about when does a physical change occur.

Physical changes occur when the substance undergoes a transition in the physical properties. Any change in the state, shape, color, or size of the object is said to be a physical change. They are generally known as temporary changes. The physical change can either be reversible or irreversible.

A physical change arises due to changing physical properties, i.e., size, shape or state, etc. Generally, physical change is caused by applying force or energy to the object. During a physical change, the total internal energy before and after the reaction or change remains the same. This means that the bonds of the object or substance remain intact. It does not break to form a new substance.

Let us understand a common example of physical change that is the melting of butter or vice versa. For melting butter, energy is required. Now this energy should be sufficient enough to change the state of the butter and does not break the bonds. When the butter acquires this energy, its molecules gain energy and come in rapid motion. Due to this, they only get apart and change into a liquid state. And hence physical change occurs.

buttered 18641 1280 — Image Credit: https://pixabay.com/photos/buttered-toast-food-bread-18641/

This change can be reversed, and butter can regain its original state on freezing, thus leading to phase change. Now physical change can also occur by changes in size, shape, odor, color, temperature, or pressure. Now when you break a pencil into two halves, its shape and size both get changed, and hence physical change has occurred.

Image Credit: Andy Schmitz, Sodium chloride dissolution, CC BY 3.0

Let’s take another case of sugar dissolving into the water. Now, this is a common example of reversible physical change. Many a time, it is confused to be a chemical change. For this, let us see how a physical change occurs. On dissolving sugar into water, no new substance is formed with no chemical reaction. During the process, the thing that happens is the change in form. The identity of both the solute and solvent remains the same. Here the water that is our solvent gets its molecules further apart, and sugar molecules fill that space. Hence this process occurs.

Now it is easy to reverse back the process and generate sugar back from the solution. The vaporization process, along with condensation and crystallization, will bring back the molecule. Hence now we know when does a physical change occur.

Frequently Asked Questions (FAQs)

Name two types of changes that can occur.

There are two types of changes that are known to humans; chemical change and physical change.

The change that forms a new substance by altering the chemical composition of the substance is said to be a chemical change. All the modifications that happen in the physical characters are inferred as physical change. There is no formation of new substances during the physical change.

Explain the physical change.

The changes happening about the physical properties of the object, substance, or compound is said to be physical change.

It involves changes in size, shape, color, odor, temperature, or pressure. Physical changes are said to be temporary changes. They can be reversed to bring back to the primary state, and some are irreversible too. E.g.:- broken glass, tearing paper, chopping vegetables.

When does a physical change occur?

Physical changes can be reversed or stay irreversible depending upon the situation.

A physical change occurs when there is any kind of alteration in the physical properties of the object. The changes can be just temporary or become irreversible. These changes do not lead to the formation of any new substance.

Is physical change temporary or permanent change?

Physical changes can be reversed back to their initial state by physical means.

Since physical change can be reversed, it is said to be a temporary change. The chemical change is known to be a permanent change. But remember, not all physical changes are reversible, like cutting trees into logs.

How to know the physical change has taken place?

Since the physical change brings changes in the physical properties of the substance, it can easily be seen.

If you see a change in any physical characteristics of the object, know that physical change has taken place. For example, when you drop a glass, it breaks into smaller pieces. The size and shape get deformed on hitting the floor. Hence physical change has occurred.

What are the signs of physical changes?

The change in physical properties is classified as physical change.

The signs of physical change are shape, size, color, matter, odor, temperature, and pressure. Any change in the following properties indicates that the physical change has taken place. These changes can clearly be observed by us and in the most cases are reversible.

Also Read:

The Definitive Guide: Difference Between Simple and Physical Pendulum

June 18, 2024October 30, 2021 by Keerthi Murthi

The primary difference between a simple pendulum and a physical pendulum lies in their motion, mass distribution, and the factors affecting their period. While a simple pendulum exhibits simple harmonic motion, a physical pendulum undergoes a more complex motion involving both simple harmonic and rotational components. Additionally, the period of a physical pendulum depends on its mass distribution and the distance between the pivot point and the center of mass, unlike the simple pendulum, which is solely determined by its length.

Understanding Simple Pendulum

A simple pendulum is an idealized model of a pendulum, where the mass is concentrated at a single point and the pendulum rod is assumed to be massless and inextensible. The motion of a simple pendulum is described by the following equation:

$$T = 2\pi\sqrt{\frac{L}{g}}$$

Where:
– $T$ is the period of the pendulum
– $L$ is the length of the pendulum
– $g$ is the acceleration due to gravity

The key characteristics of a simple pendulum are:

Simple Harmonic Motion: The displacement of a simple pendulum is directly proportional to the restoring force acting on it, resulting in simple harmonic motion.
Amplitude Limitation: The amplitude of a simple pendulum is limited by the angle of the swing, typically less than 15 degrees.
Massless Rod: The mass of the pendulum rod is assumed to be negligible, and the entire mass is concentrated at a single point.
Constant Length: The length of the pendulum rod is assumed to be constant and unaffected by factors such as temperature or other environmental conditions.

Understanding Physical Pendulum

A physical pendulum, on the other hand, is a more realistic model of a pendulum, where the mass is distributed along the length of the pendulum rod. The motion of a physical pendulum is described by the following equation:

$$T = 2\pi\sqrt{\frac{I}{mgd}}$$

Where:
– $T$ is the period of the pendulum
– $I$ is the moment of inertia of the pendulum
– $m$ is the mass of the pendulum
– $g$ is the acceleration due to gravity
– $d$ is the distance between the pivot point and the center of mass of the pendulum

The key characteristics of a physical pendulum are:

Complex Motion: The motion of a physical pendulum is a combination of simple harmonic motion and rotational motion, resulting in a more complex behavior.
Mass Distribution: The period of a physical pendulum depends on its mass distribution and the distance between the pivot point and the center of mass, unlike the simple pendulum, which is solely determined by its length.
Moment of Inertia: The moment of inertia of the physical pendulum plays a crucial role in determining its period, as it reflects the distribution of mass along the pendulum.
Amplitude Flexibility: The amplitude of a physical pendulum can be large or small, depending on its shape and mass distribution.
Environmental Factors: Factors such as temperature changes and air resistance can affect the period of a physical pendulum clock, as they can influence the dimensions and mass distribution of the pendulum.
Gravitational Variations: The period of a physical pendulum is also affected by variations in the gravitational pull at different locations and elevations.

Comparison of Simple and Physical Pendulum

To further highlight the differences between simple and physical pendulums, let’s compare them in a tabular format:

Characteristic	Simple Pendulum	Physical Pendulum
Motion	Simple harmonic motion	Complex motion (combination of simple harmonic and rotational)
Mass Distribution	Mass concentrated at a single point	Mass distributed along the length of the pendulum
Period Formula	$T = 2\pi\sqrt{\frac{L}{g}}$	$T = 2\pi\sqrt{\frac{I}{mgd}}$
Moment of Inertia	Not explicitly considered	Plays a crucial role in determining the period
Gravity Dependence	Frequency not explicitly related to mass distribution	Frequency related to the square root of the force of gravity
Length Dependence	Period increases as the square root of the length	Relationship involves the distribution of mass along the pendulum and the distance from the pivot to the center of mass
Environmental Factors	Length unaffected by temperature changes	Temperature changes can affect the dimensions and mass distribution, impacting the period
Air Resistance	Negligible effect	Can affect the accuracy of the pendulum clock
Gravitational Variations	No effect	Variations in gravitational pull affect the pendulum’s period

Practical Applications and Examples

Simple and physical pendulums have various practical applications in science, engineering, and everyday life:

Timekeeping: Both simple and physical pendulums have been used in the design of pendulum clocks, with physical pendulums being more commonly used due to their higher accuracy and stability.
Seismometers: Physical pendulums are used in seismometers to detect and measure the motion of the Earth’s surface during earthquakes.
Metronomes: Simple pendulums are often used in metronomes, which are devices used to maintain a steady beat or tempo in music.
Toys and Demonstrations: Simple and physical pendulums are commonly used in educational settings and toys to demonstrate the principles of oscillatory motion and the effects of various parameters on the period.

Numerical Examples

Simple Pendulum: Suppose a simple pendulum has a length of 1 meter. Calculate its period.
Given: $L = 1 \text{ m}$, $g = 9.8 \text{ m/s}^2$
Substituting in the formula: $T = 2\pi\sqrt{\frac{1 \text{ m}}{9.8 \text{ m/s}^2}} = 2\pi\sqrt{\frac{1}{9.8}} = 2.00 \text{ s}$
Physical Pendulum: Consider a physical pendulum in the form of a uniform rod with a length of 1 meter and a mass of 0.5 kg. The distance between the pivot point and the center of mass is 0.5 meters. Calculate the period of the pendulum.
Given: $L = 1 \text{ m}$, $m = 0.5 \text{ kg}$, $d = 0.5 \text{ m}$, $g = 9.8 \text{ m/s}^2$
The moment of inertia for a uniform rod is $I = \frac{1}{12}mL^2$
Substituting in the formula: $T = 2\pi\sqrt{\frac{\frac{1}{12}(0.5 \text{ kg})(1 \text{ m})^2}{(0.5 \text{ kg})(9.8 \text{ m/s}^2)(0.5 \text{ m})}} = 1.41 \text{ s}$

These examples illustrate the differences in the period calculations for simple and physical pendulums, highlighting the role of the moment of inertia and the distance between the pivot point and the center of mass in the case of the physical pendulum.

Conclusion

In summary, the primary difference between a simple pendulum and a physical pendulum lies in their motion, mass distribution, and the factors affecting their period. While a simple pendulum exhibits simple harmonic motion and its period is solely determined by its length, a physical pendulum undergoes a more complex motion and its period depends on its mass distribution, moment of inertia, and the distance between the pivot point and the center of mass. Understanding these differences is crucial in various applications, from timekeeping and seismology to educational demonstrations and toys.

References

Principles of Physics: A Calculus-Based Text, 5th Edition, by Raymond A. Serway and John W. Jewett, Jr.
Chapter 24: Oscillations, by Luis Anchordoqui, Lehman College, CUNY.
Physical Pendulum, GeeksforGeeks.
Simple Pendulum vs. Physical Pendulum, Purdue University Physics Demonstrations.
Simple Pendulum vs. Physical Pendulum, Vaia.com.