S.I. base units and derived units
TLDRThis video script introduces the concept of SI base and derived units, essential for accurate measurements in physics. It explains the seven SI base units, including meter, kilogram, second, Kelvin, Ampere, mole, and Candela, and their role in forming all other units. The script also demonstrates how to derive units for speed, force, and work, highlighting the importance of writing equations in line and the conventions for unit names and symbols. It emphasizes the neatness of derived units like Newtons and Joules, which simplify complex expressions, and notes the lowercase usage for unit names, with exceptions for those named after individuals.
Takeaways
- 📏 SI Base Units: There are seven fundamental SI units, including the meter for length, kilogram for mass, second for time, Kelvin for temperature, Ampere for electric current, mole for quantity, and Candela for luminous intensity.
- 🔍 Derived Units: Units like speed and force are derived from the base units using equations, such as speed being meters per second (m/s).
- 🚀 Equations for Units: The script explains how to derive units for physical quantities using equations, such as acceleration being meters per second squared (m/s²).
- 📚 Newton as Derived Unit: The Newton is a named derived unit for force, equal to one kilogram meter per second squared (kg m/s²).
- 🔧 Joules for Energy: The unit for work and energy, the Joule, is derived from the units of force and distance, equal to one kilogram meter squared per second squared (kg m²/s²).
- 📐 Unit Conventions: Units are written with a lowercase first letter, except for symbols named after a person, which use a capital letter.
- 🔡 Unit Symbols: Symbols for units named after people, like Newton (N), Joule (J), Hertz (Hz), and Pascal (Pa), have capital letters.
- 🔑 Prefixes and Units: Some units, like the kilogram, have prefixes added to them to denote multiples, such as 'kilo' for thousand (kg).
- 🔠 Kelvin Exception: Kelvin is an exception to the lowercase rule, being written with an uppercase 'K' because it is named after Lord Kelvin.
- 📉 Units Not Named After People: Base units like meter, second, and mole do not have capital letters in their symbols, reflecting they are not named after individuals.
- 📝 Writing Equations: It's recommended to write physics equations in line rather than as fractions for neatness, especially with complex units.
Q & A
What are the SI base units?
-The SI base units are seven fundamental units used in the International System of Units, which are the meter (m) for length, kilogram (kg) for mass, second (s) for time, Kelvin (K) for temperature, Ampere (A) for electric current, mole (mol) for the amount of substance, and Candela (cd) for luminous intensity.
What is the difference between SI base units and derived units?
-SI base units are the fundamental units from which all other units are derived. Derived units, on the other hand, are units that are created from combinations of the base units, often using equations from physics to define them, such as meters per second for speed.
How is the unit for speed derived from the SI base units?
-The unit for speed is derived from the equation for speed, V = distance/time. Since the unit for distance is the meter and the unit for time is the second, the derived unit for speed is meters per second (m/s).
What is the equation for acceleration and how is its unit derived?
-Acceleration is given by the equation a = Δv/Δt, where Δv is the change in velocity and Δt is the change in time. Since velocity has units of m/s and time has units of seconds, the unit for acceleration is meters per second squared (m/s²).
What is the SI unit for force and how is it derived?
-The SI unit for force is the Newton (N), which is derived from the equation F = ma, where m is mass in kilograms (kg) and a is acceleration in meters per second squared (m/s²). Therefore, 1 Newton is equal to 1 kg m/s².
What is the relationship between the Newton and the base units?
-The Newton is a derived unit expressed in base units as 1 kg m/s², representing the force exerted on a mass of 1 kilogram accelerating at 1 meter per second squared.
How is the unit for work done derived?
-The unit for work done is derived from the equation for work, W = F × d, where F is force in Newtons and d is distance in meters. Thus, the unit for work is the Joule (J), which is equal to one kilogram meter squared per second squared (kg m²/s²).
What is the convention for writing the names and symbols of SI units?
-The names of SI units are always written in lowercase, while their symbols may be uppercase or lowercase depending on the unit. For units named after a person, such as Newton (N), Joule (J), Hertz (Hz), and Pascal (Pa), the symbol typically starts with a capital letter, but the word is lowercase.
Why is the Kelvin written with an uppercase 'K'?
-The Kelvin is written with an uppercase 'K' because it is named after Lord Kelvin, making it one of the few units named after a person, and thus its symbol is capitalized.
What is the difference between the kilogram and the gram in terms of their status as SI base units?
-The kilogram (kg) is the SI base unit for mass, while the gram (g) is not a base unit but a derived unit, which is 1/1000th of a kilogram. The prefix 'kilo-' is used to denote this relationship.
Why are SI units important in scientific calculations?
-SI units are important in scientific calculations because they provide a standardized system of measurement that ensures consistency, accuracy, and clarity in scientific communication and experimentation.
Outlines
📏 Introduction to SI Units in Physics
This paragraph introduces the concept of SI base and derived units in physics. It explains the importance of distinguishing between these two types of units and emphasizes the use of SI units for calculations. The SI base units include the meter for distance, kilogram for mass, second for time, Kelvin for temperature, Ampere for electrical current, mole for the quantity of a substance, and Candela for luminous intensity. The paragraph also demonstrates how to derive units for specific quantities, such as speed (meters per second) and acceleration, using the base units and their respective equations. It highlights the convenience of using derived units like Newtons for force, which simplifies the expression of complex units.
🔤 Unit Notation and Naming Conventions
The second paragraph delves into the conventions of writing and naming units. It points out that units are always written with a lowercase first letter, except for the symbols associated with units named after a person, which are capitalized. Examples include Newton (N), Joule (J), Hertz (Hz), and Pascal (Pa). The paragraph also clarifies that base units like meter (m), kilogram (kg), and second (s) do not have a capital letter in their symbol, while derived units named after individuals do. It further explains that the gram is not a base unit and is prefixed with 'kilo-' to become the kilogram, and that the Kelvin is an exception as it is named after Lord Kelvin and thus is written with an uppercase 'K'.
Mindmap
Keywords
💡SI base units
💡Derived units
💡Meter
💡Kilogram
💡Second
💡Kelvin
💡Ampere
💡Mole
💡Candela
💡Newton
💡Joule
Highlights
Introduction to SI base units and derived units in physics.
Explanation of the difference between base and derived units.
Seven SI base units are meter, kilogram, second, Kelvin, Ampere, mole, and Candela.
Base units can form any other unit used in physics.
Derived units are created from base units using equations.
Speed's unit is meter per second, derived from the speed equation.
Writing physics equations in line is a common practice.
Force's unit is derived from mass and acceleration units.
Acceleration's unit is meters per second squared.
Newton is a derived unit for force, equal to kilogram meter per second squared.
Work's unit, the joule, is derived from force and distance units.
Explanation of how to derive the unit for work (joule).
Naming conventions for units and their symbols.
Units named after people have capital letters in their symbols.
Base units are always written with lowercase letters except for Kelvin.
Kelvin is an exception with an uppercase letter due to being named after Lord Kelvin.
Explanation of the lowercase 'd' for Candela.
Importance of using correct case for units and their symbols in scientific writing.
Transcripts
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