Short notes of chapter 1 measurement and experimentation of class 9

 * Physical quantity -

A measurable quantity is called as a physical quantity.

Example length, Mass ,time ,temperature ,pressure density, volume ,weight,force etc.,  .

A physical quantity can be expressed as a product of magnitude and a unit.

Eg. Height of a boy= 163 cm

Weight of a bat= 1.2 kg

Physical quantity = magnitude × unit

* Measurement-

Measurement is a process of comparison of an unknown quantity with a known standard quantity of same kind or nature.

Q1. Is it possible to measure height of a person by using 1 kg of standard mass ?

Ans. No, it is not possible to measure height of a person by using 1 kg of standard mass. Because height and mass both are different physical quantities.

*Fundamental quantity-

Those physical quantities which does not depend on any other quantities are called as fundamental quantities.eg. length, time, temperature ,current, mass etc.,

* fundamental unit-

Units of fundamental quantities are known as fundamental units. Fundamental units cannot be related to any other units. Or in other words fundamental units are independent of all other units.eg m-metre,s- second,A-ampere,K- Kelvin,kg-kilogram etc.,

* Derived quantity-

Derived quantities are those physical quantities which depends on the fundamental quantities or can be related to it. Example area volume, density ,weight, velocity,acceleration etc.,

* Derived unit-

Units of a derived  quantity are known as derived unit. Directly or indirectly all derived units depends on the fundamental units only. Example velocity,

V = displacement / time 

    = m/ s

    = ms-¹

Acceleration= rate of change in velocity/  time

                      = ᇫv / ᇫt

                       = ms-¹ / s

                        = ms-²

Force = mass × acceleration

F = m × a

    = 1 kg × ms-²

    = 1N

Now, pressure = thrust / area

                          = 1N / m²

                          = 1 pascal 

                          = 1 Pa

* System of units :

1. FPS (British )

2.CGS (French)

3.MKS (metric)

4.SI (international system of unit)

Q. Why SI system was introduced in the year 1960 ?

Ans. To maintin uniformity of units across the world.

* Prefixes before units:

10²⁴ = y ( yoeto)

10-²¹ = z (zepto)

10‐¹⁸ = a (atto)

10-¹⁵  = f (femto)

10‐¹²  = p (pico)

10-⁹ = n (nano)

10-⁶ = μ (micro)

10-³  = m ( milli)

10-²  = c (centi)

10-¹ = d (deci)

10⁰ = 1

10¹ = da (deca)

10² = h (hecto)

10³ = k (kilo)

10⁶ = M (mega)

10⁹ = G (giga)

10¹² = T (tera)

10¹⁵ = P (peta)

10¹⁸ = E (exa)

10²¹ = Z (zetta)

10²⁴ = Y (yotta)