# Chapter 2 – Physical Quantities and Measurement

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

A physical quantity is the attribute of an entity that can be measured. For example, the length of a pipe or the mass of an object is a physical attribute. But do you know why we measure the physical quantities? Measurement is the process of linking a physical quantity to its unit, which makes it quantifiable.

Do you know the difference between mass and volume? The matter contained in an object or a body is its mass. The space occupied by an object or body in the universe is known as its volume. Let us understand the concept of density and its importance.

#### Density

The ratio of the mass of an object to its unit volume is known as density.

⍴= M/V

Where ⍴= density of the substance

M= mass of the substance

V= volume of the substance

Density is measured in Kilogram per metre cube or Kg/m3, which is its S.I. unit. The symbol of density is rho (⍴).

#### Relative Density

The ratio of the density of a material to the density of reference material is known as its relative density, also known as specific density. For most liquids, the relative density is calculated with respect to the density of water.

Relative density = Density of a material/ Density of reference material

#### Measurement of Density of Solids

To measure the density of regular solids, find the mass of the regular solid. You can use a beam balance to know the mass.

Calculate the volume of the solid using the prescribed formulas. Some common shapes and their volumes are given by –

• The volume of a cube = Cube of measure of a side
• Volume of a cuboid = Length x breadth x height
• Volume of a cylinder = 4/3 x pi x cube of radius
• Volume of sphere = 4 x pi x cube of radius
• The volume of cylinder = pi x square of radius x height

Using the values of mass and volume, find the density of the solid by

Density = mass/ volume

To find the measurement of the density of irregular solids, we must first determine their mass and volume.

Using a physical balance, we can find the mass of an irregular solid. To find the volume of an irregular solid, we can’t use any pre-described formulas. We use a different approach here using the concept of volume that states that the amount of space taken by an object is its volume.

First, we take a cylinder or any other container that has markings for volume. Then, fill this container with water and note the initial reading. Next, we dip the object in this water, increasing the container’s water level. This elevated water reading is noted in the final reading. The difference between the two markings will give us the object’s volume, which has an irregular shape.

After we determine the mass and volume of the irregular solid, the density is given by

D = mass/volume

#### Measurement of Density of Fluids

A specially designed bottle, known as the density bottle, is used for measurement of the density of fluids.

• First, we find the mass of the bottle with the help of a balance. Next, we fill this bottle with water and again measure its mass.
• Then, we empty all the water from this bottle.
• We fill the emptied and dried bottle with the liquid whose density we want to find.
• Next, we measure the mass of the liquid-filled density bottle.
• Using these measurements, we first find the mass of water.

Mass of water = mass of bottle filled with water – the mass of the empty bottle

Mass of liquid = mass of bottle filled with liquid – the mass of the empty bottle

• Now, we know that the density of water is 1gm/cm3. So, the value of the mass of water in the volume is the same as the volume of the density bottle.
• Therefore, the density of the liquid = mass of liquid/ mass of water.

#### Floatation and Sinking

The Law of Floatation states that “The weight of the solid floating in a fluid is equal to the weight of the fluid displaced by immersed part of the solid.”

Let us understand the concept of floatation and sinking of a substance. An object with its relative density with water less than one floats on the surface of the water, while an object with a relative density of more than one sinks when placed in water. So, floatation and sinking depend upon the relation between the density of water and the object’s density.

Two forces act on an object when it is immersed in a liquid:

• The first force ties to make the object sink in the liquid. It is the weight of the body that acts perpendicularly downwards.
• The second force is the buoyant force that acts vertically upwards. The buoyant force is equal to the liquid’s weight that the object has displaced when immersed in the liquid.
• So, the volume of an object x density of an object = Volume of the displaced liquid x density of the liquid.

#### Comparison of Densities

The three states of matter, i.e., solid, liquid, and gas, possess different properties. The molecular placement in the three states of matter is different and so are their intermolecular spaces. The densities of these states of matter also differ according to the arrangement of their molecules.

The comparison of densities in the three states of matter is given below:

 State of matter Solid Liquid Gas Molecule placement Molecules are close together Molecules are spread apart Molecules are very far apart Intermolecular space Least intermolecular space Moderate intermolecular space Highest intermolecular space Density Density is the highest Medium-density Lowest density

#### Conclusion

The measurement of density helps us understand the process of sinking and floatation. To compare the different physical quantities, we use measurement expressed in the form of units. The physical quantities and measurements are essential to apply the concepts of physics in the real world.

#### FAQs

1. What is the unit of relative density?
Since relative density is the ratio of an object’s density with respect to reference material, it is a dimensionless quantity.
2. What device is used for the measurement of the density of fluids?
A density bottle is used to measure the density of fluids.
3. What is buoyancy?
The buoyancy of an object is its virtue of floating on the liquid’s surface.

To know more about the concepts of physical quantities and measurements, visit the MSVgo app. With interactive videos, quizzes, interactive games on the app, you can hone your knowledge.

### High School Physics

• Alternating Current
• Atoms
• Communication Systems
• Current Electricity
• Dual nature of Radiation and Matter
• Electric Charges and Fields
• Electricity
• Electromagnetic Induction
• Electromagnetic Waves
• Electron Beams and Radioactivity
• Electrons and Photons
• Electrostatic Potential and Capacitance
• Fluid Pressure
• Force and Acceleration
• Force And Laws Of Motion
• Gravitation
• Internal Energy
• Kinetic Theory
• Law of motion
• Light – Reflection And Refraction
• Magnetic Effects Of Electric Current
• Magnetism and Matter
• Management Of Natural Resources
• Mechanical properties of Fluids
• Mechanical properties of Solids
• Motion
• Motion in a plane
• Motion in a straight line
• Moving Charges and Magnetism
• Nuclear Energy
• Nuclei
• Oscillations
• Our Environment
• Paths of Heat
• Physical world
• Ray optics and optical instruments
• Semiconductor Devices
• Semiconductor Electronics: Materials, Devices and Simple Circuits
• Simple Machines
• Sound
• Sources Of Energy
• Specific and Latent Heats
• Spherical Mirrors
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• Systems of Particles and Rotational motion
• Thermal properties of matter
• Thermodynamics
• Units and Measurement
• Vectors, Scalar Quantities and Elementary Calculus
• Wave Optics
• Waves
• Work, Power and Energy

### High School Chemistry

• Acids, Bases and Salts
• Alcohols, Phenols and Ethers
• Aldehydes, Ketones and Carboxylic Acids
• Aliphatic and Aromatic Hydrocarbons
• Alkyl and Aryl Halides
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• Analytical Chemistry
• Atomic Structure
• Atoms And Molecules
• Basic concepts of Chemistry
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• Carboxylic acids and Acid Derivatives
• Chemical Bonding and Molecular Structures
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• Chemistry in Everyday Life
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• Classification of Elements
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• States of Matter
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• Study of Compounds
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• The d-block and f-block elements
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• The p-Block Elements
• The Periodic Table
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### High School Biology

• Absorption and Movement of Water in Plants
• Adolescent Issues
• Anatomy of Flowering Plants
• Animal Kingdom
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• Biodiversity and Conservation
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• Cell – Unit of Life
• Cell Cycle and Cell Division
• Cell Division and Structure of Chromosomes
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• Circulation
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• Diversity In Living Organisms
• Ecosystem
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• How Do Organisms Reproduce?
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• Microbes in Human Welfare
• Mineral Nutrition
• Molecular Basis of Inheritance
• Morphology of Flowering Plants
• Neural Control And Coordination
• Nutrition in Human Beings
• Organism and Population
• Photosynthesis
• Photosynthesis in Higher Plants
• Plant Growth and Development
• Plant Kingdom
• Pollination and Fertilization
• Pollution; Sources and its effects
• Principles of Inheritance and Variation
• Reproduction and Development in Angiosperms
• Reproduction in Organisms
• Reproductive Health
• Respiration in Human Beings
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• Respiratory System
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• Strategies for Enhancement in Food Production
• Structural Organisation in Animals
• Structural Organisation of the Cell
• The Endocrine System
• The Fundamental Unit Of Life
• The Living World
• The Nervous System and Sense Organs
• Tissues
• Transpiration
• Transport in Plants

### High School Math

• Algebra – Arithmatic Progressions
• Algebra – Complex Numbers and Quadratic Equations
• Algebra – Linear Inequalities
• Algebra – Pair of Linear Equations in Two Variables
• Algebra – Polynomials
• Algebra – Principle of Mathematical Induction
• Algebra – Quadratic Equations
• Binomial Theorem
• Calculus – Applications of Derivatives
• Calculus – Applications of the Integrals
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• Geometry – Area
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• Geometry – Introduction to Euclid’s Geometry
• Geometry – Three-dimensional Geometry
• Geometry – Lines and Angles
• Geometry – Quadrilaterals
• Geometry – Straight Lines
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• Linear Programming
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• Mensuration – Areas
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• Number Systems
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• Permutations and Combinations
• Probability
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• Trignometry – Height and Distance
• Trignometry – Identities
• Trignometry – Introduction

### Middle School Science

• Acids, Bases And Salts
• Air and Its Constituents
• Basic Biology
• Body Movements
• Carbon and Its Compounds
• Cell – Structure And Functions
• Changes Around Us
• Chemical Effects Of Electric Current
• Chemistry in Your Life
• Coal And Petroleum
• Combustion And Flame
• Components Of Food
• Conservation Of Plants And Animals
• Crop Production And Management
• Electric Current And Its Effects
• Electricity And Circuits
• Elements and Compounds
• Fibre To Fabric
• Food production and management
• Force And Pressure
• Forests: Our Lifeline
• Friction
• Fun With Magnets
• Garbage In, Garbage Out
• Getting To Know Plants
• Health and Hygiene
• Heat
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• Life Processes: Nutrition in Animals and Plants
• Light, Shadows And Reflections
• Materials: Metals And Non-Metals
• Matter and Its States
• Metals and Non-metals
• Micro Organisms: Friend And Foe
• Motion And Measurement Of Distances
• Motion And Time
• Nutrition In Animals
• Nutrition In Plants
• Organization in Living Things
• Our Environment
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• Reaching The Age Of Adolescence
• Reproduction In Animals
• Reproduction In Plants
• Respiration In Organisms
• Rocks and Minerals
• Separation Of Substances
• Simple Machines
• Soil
• Some Natural Phenomena
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• Sound
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• Structure of Atom
• Synthetic Fibers And Plastics
• The Living Organisms And Their Surroundings
• Transfer of Heat
• Transformation of Substances
• Transportation In Animals And Plants
• Universe
• Waste-water Story
• Water: A Precious Resource
• Weather, Climate And Adaptations Of Animals To Climate
• Winds, Storms And Cyclones

### Middle School Math

• Addition
• Area and Its Boundary
• Boxes and Sketches
• Data Handling
• Fun With Numbers
• Heavy and Light
• How Many
• Long And Short
• Mapping
• Measurement
• Money
• Multiplication and Factors
• Multiply and Divide
• Numbers
• Parts and Wholes
• Pattern Recognition
• Patterns
• Play With Patterns
• Rupees And Paise
• Shapes And Angles
• Shapes And Designs
• Shapes and Space
• Similarity
• Smart Charts
• Squares
• Subtraction
• Tables And Shares
• Tenths and Hundredths
• Time
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