##### Chapter 1

## Physical Quantities and Measurement

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

#### Introduction

**physical quantities are measured**.

Scientists across the globe adopted an international unit of measurements(S.I.) to improve communication.

Physical quantity | S.I. unit for Measurement | Symbol |

Mass | Kilogram | Kg |

Length | Meter | m |

Time | Second | s |

Temperature | Kelvin | K |

Here in this section, we will discuss **Measurement of Volume and Density**, **calculation of speed, and Measurement of area** of any given object.

Volume is defined as the quantity of space occupied by an enclosed object. In this section, we will see how the volume of different things is measured.

Few of the real-life applications are,

- We
**measure the volume**of liquids while cooking. - We
**measure the volume**of fuel to be filled in vehicles, and so on.

Volume of a solid object

Consider you have a tangible object whose volume needs to be determined. It can be found by multiplying its length, width, and height.

So, the **volume of any solid object= length X breadth X height**

Now, consider finding the volume of a cube.

In this case of cube, length=breadth=height=l

So, Measurement of Volume for cube = l^{3}

Thus the standard unit of volume of any solid object is a cubic meter or m^{3}.

Volume of any liquid

Liquids are physical quantities that do not have a definite shape. Thus, a measuring cylinder is used to **measure the volume** of any liquid. A measuring cylinder is a glass cylinder with

markings on the sidewall. You need to pour the liquid and take the reading once it comes to rest.

Measuring cylinder

Suppose Arjun and Seema have participated in a 200m race competition in school. Arjun takes 200 seconds, while Seema takes 400 seconds to finish the race. Can you tell me who runs faster?

Here, in this section, you will get an answer to this question.

**What is speed?**

Speed finds out how fast or how slow an object is moving. It is defined as the distance covered by any object in unit time. Suppose a bike covers a distance of 100 km in 1 hour, then we can say its speed is 100km per hour.

Speed = Total distance covered(d)/Total time taken(t)

he SI unit of speed is meters/second or m/s. It is measured using a speedometer.

Now let us consider our previous example and **calculate the speed** for them.

Speed of Arjun=200/200= 1 m/s

Speed of Seema=200/400= 0.5 m/s

Thus, we can say that Arjun runs faster than Seema.

An object covers the maximum distance in a given time when it is travelling at the highest speed. Also, the same thing will cover the minimum distance when it is travelling at the lowest speed.

The area is the space occupied by a closed two-dimensional object. In other words, it is the number of squares occupied by a closed flat figure.

In a real-life scenario, we measure the area of the wall to find out the expenses that we might have to bear to paint that wall.

S.I. unit of area is a square meter or m^{2}.

**Measurement Of Area Of A Regular Shaped Body**

A regularly shaped body or a regular solid is a type of object with a fixed geometrical shape like a plate, compass box, book, etc.

**Measurement Of Area Of A Regular Shaped Body using formula** gives,

Area of a square = l^{2}, where l is the length

Area of a rectangle=l X b, where l=length and b=breadth

Area of a circle = **π**r^{2}, where r=radius of circle

Area of a triangle=1/2 x b x h , where b=breadth and h=height

Consider a wooden ball and a brass ball of equal sizes, i.e., same volumes. Now can you tell which is heavier? Yes, the brass ball is heavier than the wooden ball as it has more mass. Thus, Density is defined as mass per unit volume.

Density= Mass(m)/Volume(v)

A simple example, where a rock sinks in a glass of water, indicates it is denser than water.

S.I. unit of Density is kg/m^{3}.

**For Measurement of Density of Regular solid, **we would need,

- Mass of the regular solid that is measured using a weighing scale or any physical balance.

- The volume of the regular solid that can be measured using the below formulas

Volume of a cube = (length)^{3}

Volume of a cuboid = length X breadth X height

Volume of a cylinder = **π** r^{2}h , where r= radius and h=height of the cylinder

Volume of a sphere= 4/3 **π** r^{3}, where r is radius of the sphere

**Physical quantities and Measurement** are expressed using standardized units. Volume is the space occupied by a three-dimensional object, whereas area is the space occupied by two-dimensional objects. An item with a higher density is densely packed as compared to the other things. We increase the vehicle’s speed when there is less traffic and decrease its speed during high traffic.

- Name two instruments that are used for the
**Measurement of the Volume**of a liquid?

A measuring cylinder and measuring beaker are used to measure the volume of the liquid. - State the C.G.S unit used for
**Physical quantities and Measurement**?**Physical quantity****C.G.S unit for Measurement****Symbol****Mass**Gram gm **Length**Centimeter cm **Time**Second s **Temperature**Kelvin K - Find the measurement of the area of the triangle with a breadth of 4m and a height of 12m.

Area of a triangle= 1/2 x b x h**using formula**

=1/2 x 4 x 12

=212

Area of triangle = 24 m^{2}

- What care needs to be taken while measuring the volume of a liquid?

The measuring cylinder needs to be kept on a horizontal surface, and the liquid measured should be at rest. - If you have steel and glass balls of the same size, which has a higher density?

The steel ball will have a higher density as it is heavier than the glass ball. - The speed of the train is 200km/hr while that of an aeroplane is 500km/hr. Which travels faster?

Aeroplanes travel faster than trains.