Need for Measurement

Measurement is necessary to know the exact size, amount, or quantity of things. It helps us perform tasks accurately, compare objects, and communicate clearly. Without measurement, everyday activities like cooking, building, shopping, and scientific work would be difficult and unreliable.

1.0Definition of Measurement

Measurement is the process of finding out how big, how much, or how many of something there is by using a standard unit. It works by comparing what you want to measure with something you already know, like a ruler or a scale, to get a number that tells you the size, weight, time, temperature, or amount of that thing. 

2.0Importance of Measurement

• Helps us find the exact size, weight, or amount of things.
• Ensures accuracy and fairness in daily activities like cooking and shopping.
• Allows easy comparison between different objects or quantities.
• It is essential for science, medicine, and engineering to work correctly.
• Helps us plan, build, and communicate clearly and safely.

3.0SI Unit Prefixes

4.0Physical Quantities

Physical quantities are things we can measure in the physical world. Some, like length, mass, and time, are basic and can’t be broken down further—these are called fundamental quantities. Others, like speed, force, and energy, are made by combining these basic ones and are called derived quantities. Every physical quantity has a standard unit, like meters or seconds, set by systems such as the International System of Units (SI) so everyone measures things the same way.

Types of Physical Quantities

1. Fundamental Quantities: The quantities which do not depend upon other quantities for their complete definition are known as Fundamental or Base quantities.

2. Derived Quantities: The quantities which can be expressed in terms of fundamental quantities are referred to as derived quantities.

• Speed = $\frac{Distance}{Time}=\frac{meters}{second}$
• Force = Mass × Acceleration=Newton
• Area = Length × Width =$Metr{e}^2$

5.0Units of Measurement

6.0Standards of Measurement

A standard is a physical reference that defines a unit of measurement. It helps ensure everyone uses the same definition when measuring something.

Types of Standards

1. Primary Standards: These are the most accurate and trusted references, usually kept and maintained by national or international labs. For example, the International Prototype Kilogram was once the global reference for mass.
2. Secondary Standards: These are carefully calibrated using the primary standards. They are used in labs for high-precision work but aren't as exact as primary standards.
3. Working Standards: These are the tools used in everyday measurements—like rulers, thermometers, or weighing scales. They are regularly checked and calibrated using secondary standards to maintain accuracy over time.

7.0Types of Measurement

8.0Accuracy, Precision, and Errors in Measurement

(a) Accuracy: How close a measurement is to the actual or true value.

(b) Precision: How consistent repeated measurements are, even if they’re not close to the true value.

(c). Errors in Measurement

1. Systematic Errors: These errors occur consistently in the same direction and affect all measurements similarly.

• Common sources: faulty or improperly calibrated instruments, zero errors, and environmental conditions.
• Note: Systematic errors can often be identified and corrected.

2. Random Errors: These occur unpredictably and vary in magnitude and direction. They arise from limitations in measurement methods or human estimation.
3. Least Count: The least count is the smallest unit or division that an instrument can measure accurately.

• Example: A vernier caliper might have a least count of 0.01 cm, meaning it can measure up to one-hundredth of a centimeter.