Here's why:
* Fundamental: They represent basic, intrinsic properties of physical objects.
* Length describes the spatial extent of an object.
* Mass describes the amount of matter an object contains and its resistance to acceleration.
* Time measures the duration of events.
* Independent: These quantities cannot be defined in terms of each other. They are distinct and independent physical concepts.
Why these are important for mechanics:
* Building Block: All other mechanical quantities can be derived from these base quantities. For example:
* Velocity: Change in length over time (m/s)
* Acceleration: Change in velocity over time (m/s²)
* Force: Mass times acceleration (kg m/s²)
* Energy: Ability to do work (kg m²/s²)
* Momentum: Mass times velocity (kg m/s)
* Consistency and Standardization: Choosing base quantities provides a consistent framework for defining and measuring all other mechanical quantities. This ensures that measurements are universally comparable.
Other considerations:
* Practicality: These quantities are easily measurable and understood.
* Historical Development: The choice of these base quantities reflects the historical development of mechanics and our understanding of fundamental physical concepts.
It's worth noting that the choice of base quantities is somewhat arbitrary and can vary depending on the specific area of physics. However, length, mass, and time are widely accepted as fundamental quantities in classical mechanics.
