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

You might have experienced measuring the length of your wall to finalize the size of the wardrobe. We constantly check the clock’s time to determine if we will make it on time to the destination. The topic **Measurements and Experimentation** is included in the Class 9 syllabus to understand better the different units and their relationship with the physical quantities like time, length, mass, temperature, etc.

The **International System of Units**, also commonly called as S.I unit system. Countries like United States, United Kingdom, Canada, and many more have widely accepted in 1960.

There are seven fundamental and two complementary units included in the SI system. They are length, time, mass, luminous intensity, current, temperature, and quantity of the substance and Angle and solid angle.

We have tabulated below the **International System of units** for better readability.

**Physical quantityS.I. unit for MeasurementSymbolMass**KilogramKg**Length**Meterm**Time**Seconds**Temperature**KelvinK**Luminous intensity**Candelacd**Current**AmpereA**Quantity of substance**molemol**Angle**Radianrad **Solid angle**Steradiansr

The prefixes used for larger measurements in the** International System of units** are tabulated below.

**PrefixSymbolMeaningDeca**da101**Hecto**h102**Kilo**k103**Mega**M106**Giga**G109**Tera**T1012**Peta**P1015**Exa**E1018

For the **measurement of length**, we can use a meter scale or vernier calipers.

A meter scale is a plastic, wooden, or metal scale with a maximum length of 1 meter or 100 cms. It is divided into 100 divisions, with each division or the least count 1mm or 0.1 cm.

We cannot use a meter scale for measurements to go up to 2 decimal places(0.01 cm).

Two scales, namely the main scale and the vernier scale, give us accuracy up to 0.01 cm.

Vernier calipers are used to measure any rod’s length, the diameter of the cylinder and sphere, etc.

A screw gauge ideally measures the wire or paper thickness. For a screw gauge, its pitch is the straight distance that the screw moves on the main scale while the circular scale completes one rotation.

You might have experienced that your friend arrived late for the class on a particular day. We have always heard that time never waits for anyone. So the teacher starts with the lecture without waiting for latecomers. So we need to understand the **measurement of time**.

We use Stopwatches in laboratories where shorter time intervals need to be measured. In contrast, you might have seen a wall clock at your homes to measure time. In this section, we will briefly discuss the working of a **simple pendulum**.

A **simple pendulum** consists of a heavy point-like object called bob that is suspended from fixed support using a string that can neither be extended nor has mass. Bob is an iron or brass ball suspended using a lightweight string from firm support.

Now when its bob is at rest at the position O. It is then released to pass horizontally from point A to point B passing through O.

It completes one oscillation when it moves from O to A, A to B, and then back to O.

Period of oscillation is the time needed by a **simple pendulum** to complete one oscillation, while the frequency of oscillation is the total number of oscillations completed in one second. The amplitude of oscillation is the maximum distance covered from the bob’s mean position on either of its side.

In this topic of **Measurements and Experimentation**, we have learned about the **International System of units** and their relations. Also, a meter scale is used for the **measurement of length** in daily life, while we prefer to use a **simple pendulum** for the **measurement of time**.

- What is a lunar month?
- It is the time duration in which the moon completes one revolution around Earth.
- How to find the least count of a screw gauge?
- =
- What is the relation between frequency and period of oscillation in a
**simple pendulum**? - =
- Give the expression to find the period for a
**simple pendulum**. - =
- T is the oscillation period, l is the string’s length, and g is the acceleration due to gravity.
- What are the prefixes used for smaller measurements and experimentation?

**PrefixSymbolMeaningdeci**d10-1**centi**c10-2**milli**m10-3**micro**10-6**nano**n10-9**pico**p10-12**femto**f10-15**atto**a10-18