Introduction to Physics: Measurement, Units, and the Foundations of Science

Physics: The Foundation of Science

What is Science?

Science is a systematic approach to understanding the natural world. It begins with curiosity and the desire to answer questions about how and why things happen.

• Science starts with a question: The process of scientific inquiry is driven by asking questions about the universe.

• Asking "why" and "how": Scientists seek to explain phenomena by understanding underlying causes and mechanisms.

• Power of science: Science is valued not only for its explanations but also for its predictive power—its ability to forecast future events or behaviors based on established principles.

Measurement in Science

The Importance of Measurement

Measurement is fundamental to science, providing a quantitative basis for observation, comparison, and prediction.

• Precision and clarity: Accurate measurements are essential for reproducibility and communication in science.

• Examples: Recipes, bank statements, and scientific experiments all rely on precise measurements to ensure consistency and reliability.

SI Units: The International System of Units

Base Units

The SI system is built on seven base units, each representing a fundamental physical quantity. All other units are derived from these base units.

Quantity	Unit	Symbol
Mass	kilogram	kg
Length	meter	m
Time	second	s
Temperature	kelvin	K
Electric current	ampere	A
Amount of substance	mole	mol
Luminous intensity	candela	cd

Additional info: In introductory physics courses, the most commonly used base units are kilogram, meter, second, and kelvin.

Base Units Used in Introductory Physics

Quantity	Unit	Symbol
Mass	kilogram	kg
Length	meter	m
Time	second	s
Temperature	kelvin	K

Defining the Meter and Kilogram

The Meter (m)

The definition of the meter has evolved over time to increase precision and universality.

• Historical definition: Originally based on a physical artifact (a platinum-iridium bar).

• Modern definition: Since 1983, the meter is defined as the distance light travels in vacuum in 1/299,792,458 of a second.

Equation:

$1\ \text{meter} = \text{distance traveled by light in vacuum in}\ \frac{1}{299,792,458}\ \text{seconds}$

The Kilogram (kg)

The kilogram is the SI base unit of mass. Historically, it was defined by a physical artifact, but this approach has limitations.

• Artifact standard: The kilogram was defined by the mass of a platinum-iridium cylinder kept in Paris.

• Problems: Physical artifacts can change over time (e.g., due to contamination or material loss), leading to inconsistencies.

• Modern redefinition: The kilogram is now defined in terms of fundamental physical constants, specifically the Planck constant (since 2019).

Additional info: The move to define the kilogram by a constant of nature ensures long-term stability and universality.

Examples and Applications of SI Units

• 1 liter of water has a mass of approximately 1 kg.

• 1 dollar bill weighs about 1 g.

• 1 nickel weighs about 5 g.

• 1 carat is 0.2 g.

• 1 metric ton is 1000 kg.

Summary Table: SI Base Units

Physical Quantity	Unit Name	Unit Symbol
Mass	kilogram	kg
Length	meter	m
Time	second	s
Temperature	kelvin	K
Electric current	ampere	A
Amount of substance	mole	mol
Luminous intensity	candela	cd

Key Takeaways

• Physics is the foundational science that seeks to explain and predict natural phenomena.

• Measurement is essential for scientific inquiry, enabling precise communication and reproducibility.

• The SI system provides a standardized set of units for all scientific measurements, with seven base units forming the foundation.

• Modern definitions of units are based on universal physical constants, ensuring consistency and accuracy worldwide.