Students can use NCERT Class 9 Advanced Science Notes and Chapter 1 Measurement Foundation of Science Class 9 Notes to understand complex concepts with ease.
Measurement Foundation of Science Notes Class 9 Advanced Science
Class 9 Measurement Foundation of Science Notes
Measurement
- Measurement is the systematic process of comparing an unknown quantity (the object you are measuring) with a known standard quantity (the unit) of the same nature.
- We can only compare quantities of the same kind. For example, you cannot measure the “weight” of a length or the “length” of a temperature.
Why Measurement Matters
- The Foundation of Physics: Physics is a quantitative science; it relies on precise data to explain how the universe works.
- Accuracy and Consistency: Whether it is calculating the dimensions of a room, the mass of an object, or the duration of an event, accurate measurement ensures that results are reliable and can be shared globally.
| Scenario | What is Measured? | Standard Unit Used |
| At the Tailor Shop | Length of cloth | Metre |
| At the Clinic | Body temperature | Degree Celsius |
| At the Grocery Store | Quantity of rice | Kilogram |
| On the Race Track | Duration of a run | Second |
Activity 1.1 Measuring the area of the classroom floor
Materials: Take three sticks of length l1:l2:l3 = 1:2:3
Procedure:
1.Divide students in 3 groups and hand over one stick to each group.
2. Each group will measure the length and width of the classroom taking stick as one unit.
| Stick 1 (Used by Group A) | Stick 2 (Used by group B) | Stick 3 (Used by group C) | |
| Length of wall | ….. unit | ….. unit | ….. unit |
| Breadth of wall | ….. unit | ….. unit | ….. unit |
| Area of floor | ….. unit2 | ….. unit2 | ….. unit2 |
3. Compare the length, breadth and area measured by different groups and try to generate conclusions between unit chosen and numerical values obtained by all the three groups.
Answer:
1. Three sticks are taken of length 30 cm, 60 cm and 90 cm. So, l1:l2:l3 = 1:2:3
2. Divided students in 3 groups A, B and C and handed over one stick to each group.
3. Each group measured the length and width of the classroom taking stick as one unit.
| Stick 1 (Used by Group A) | Stick 2 (Used by group B) | Stick 3 (Used by group C) | |
| Length of room | 12 unit | 6 unit | 4 unit |
| Breadth of room | 18 unit | 9 unit | 6 unit |
| Area of floor | 216 unit2 | 54 unit2 | 24 unit2 |
4. Compared the length, breadth and area measured by different groups.
| Measured by group A | Measured by group B | Measured by group C | |
| Length of room | 12 unit = 12 × 30 cm = 360 cm | 6 unit = 6 × 60 cm = 360 cm | 4 unit = 4 × 90 cm = 360 cm |
| Breadth of room | 18 unit = 18 × 30 cm = 540 cm | 9 unit = 9 × 60 cm = 540 cm | 6 unit = 6 × 90 = 540 cm |
| Area of floor | 216 unit = 216 × 30 cm × 30 cm = 194400 cm2 | 54 unit2 = 54 × 60 cm × 60 cm = 194400 cm2 | 24 unit2 = 24 × 90 cm × 90 cm = 194400 cm2 |
Lengths, breadths and areas measured by different groups are same.
Activity 1.2: Let’s play an estimation game
Procedure:
1. Estimate the length of the blackboard without measuring.
2. Then measure its length using a metre scale.
3. Compare the estimated and measured values. Now, calculate the inaccuracy (error) in the measurement.
Answer:
1. Estimated the length of the standard blackboard without measuring is approximately 2.5 m.
2. Then measured its length using a metre scale.
| Length of black board | |
| By eye estimation | Measured using a metre scale |
| 2.5 m | 2.4 m |
3. Compared the estimated and measured values.
Error = Estimated value – Actual value
= 2.5 m – 2.4 m = 0.1 m
Percentage error = \(\left(\frac{0.1 \mathrm{~m}}{2.5 \mathrm{~m}}\right)\) × 100% = 4%
Different Systems of Units
Historically, different regions developed their own unique ways to measure the world. However, using multiple standards often led to confusion in trade and science.
To solve this, three primary systems were established before the global adoption of the SI system:
A. The CGS System
Primarily used in laboratories and for specific scientific calculations.
- Length: centimetre (cm)
- Mass: gram (g)
- Time: second (s)
B. The FPS System
Commonly used in the United Kingdom (historically) and still widely used in the United States.
- Length: foot (ft)
- Mass: pound (lb)
- Time: second (s)
C. The MKS System
This system became the foundation for modern engineering and eventually evolved into the SI (International System of Units) used worldwide today.
- Length: metre (m)
- Mass: kilogram (kg)
- Time: second (s)
Need for a Common System of Units
Having different systems caused major difficulties in international communication, global trade, and scientific research.
Activity 1.3: Let us Compare
Materials: Ruler marked in cm and inches
Procedure:
1. Measure the length of a book using both cm and inches.
2. Compare the values and find the relation between them.
Answer:
1. Measured the length of a book using both cm and inches.
| Length of a book | |
| Measured in cm | Measured in inch |
| 25.4 cm | 10 inch |
2. Compared the values:
10 inch = 25.4 cm
∴ 1 inch = \(\frac{25.4 \mathrm{~cm} \times 1 \text { inch }}{10 \text { inch }}\) = 2.54 cm
Problems Without a Common System:
- Confusion in Trade: Buying and selling goods between countries was difficult when weights and lengths didn’t match.
- Scientific Errors: Calculations performed in one system were often miscalculated when converted to another.
- Data Sharing: It was nearly impossible for scientists to compare results accurately without a universal standard. Example: If a scientist in India measures a length in metre and a scientist in the USA measures it in foot, comparing their data is difficult and prone to error. A universal system (SI) ensures everyone “speaks the same language” of measurement.
International System of Units (SI)
The SI System (Systeme International d’Unites) is the modern, universally accepted standard of measurement used today.
SI Base Units
| Physical Quantity | SI Unit | Symbol |
| Length | Metre | m |
| Mass | Kilogram | kg |
| Time | Second | s |
| Temperature | Kelvin | K |
| Electric current | Ampere | A |
| Luminous intensity | Candela | cd |
| Amount of substance | Mole | mol |
Advantages of the SI System
- Universal: It is accepted by almost every country in the world.
- Logical: It is based on the decimal system (powers of 10), making conversions simple.
- Standardised: It ensures that a “metre” is the same length everywhere on Earth
Conversion of Units Between Systems
During unit conversion, the numerical value and the unit may change, but the magnitude of the physical quantity remains the same.
Basic Conversions
- 1 km = 1000 m
- 1 m = 100 cm
- 1 kg = 1000 g
- 1 hour = 3600 s
- The fundamental principle of measurement: It states that the magnitude of a physical quantity remains same, regardless of the system of units used to measure it.
If n = The numerical value and u = The unit of measurement then, n1u1 = n2u2