<p align="right">Last Update: <font color="#4f81bd">January 07, 2025</font></p>
## BIG IDEAS
- The modern metric system
- Length (L), mass (M), and time (T) are the most common physical quantities measured in motion.
- The measurements of physical quantities ae expressed with a number multiplied by a standardized value known as a unit.
- Using SI, and adaptation of the metric system, helps scientists communicate observations.
---
A [[Physical quantity]] is a property of an object or system that can be measured. For example, 3 liters is a measurement of volume. It means 3 times 1 liter. This volume measurement has a number and a unit. In this course the units are the SI units.
Most of [[Classical Physics|classical mechanics]] will rely on the three physical quantities: [[Length|length]], [[Mass|mass]], and [[Time|time]]. In describing [[Rest and Motion|motion]], the physical quantities might be [[Notes Vault/Physics Notes Vault/Kinematics/1D Motion/Position|position]], [[Velocity|velocity]], or [[Notes Vault/Physics Notes Vault/Kinematics/1D Motion/Acceleration|acceleration]].
In explaining motion, the physical quantities might be forces, momentum, or impulse. In studying pressure, the physical quantities might be pressure, volume, or temperature. During the energy unit, the physical quantities might be work, kinetic energy, potential energy, or power. In thermal physics, it might be specific heat or temperature. In electricity, the physical quantities might be amount of charge, resistance, or power.
![[Base Units#About Base Units]]
### Prefixes
An awesome feature of the SI system is to add a prefix to a base unit. Adding a prefix changes the scale of the measurement; the prefix acts as a multiplier. For example, the prefix centi- (1/100) can be added to meters and we are now communicating that an object is small.
Common prefixes include
| Prefix | Abbreviation | Multiplier (Fraction) | Multiplier (Exponential) |
|----------|--------------|-----------------------|---------------------------|
| deka | da | 10 | $10^1$ |
| deci | d | 1/10 | $10^{-1}$ |
| centi | c | 1/100 | $10^{-2}$ |
| milli | m | 1/1000 | $10^{-3}$ |
| kilo | k | 1000 | $10^{3}$ |
### Derived
A derived unit is a combination of other units. It’s possible to combine base with base or base with other derived units and it’s possible to combine derived with derived. Twenty two derived units have special names.
Let’s look at velocity and force then ultimately work.
Velocity is defined as a length of motion during a time interval (length / time). The length is in meters and the time is in seconds; therefore, we combine the two units to derive meters per second. This unit is shown as m/s, where the / is the symbol for “per”.
|Quantity|Dimension|SI Unit|Symbol|
|---|---|---|---|
|Length|[L]|meter|m|
|Mass|[M]|kilogram|kg|
|Time|[T]|second|s|
### The **m-** Possible Symbol
The lowercase m and the uppercase M have many meanings in physics. It’s important to watch how the letter is being used in a physics problem.
| Symbol | Meaning |
|--------|------------------|
| m | mass |
| M | large mass |
| M | Mega- |
| m | milli- |
| m | meters |
### Slide Deck
<div style="position: relative; width: 100%; height: 0; padding-top: 56.2500%;
padding-bottom: 0; box-shadow: 0 2px 8px 0 rgba(63,69,81,0.16); margin-top: 1.6em; margin-bottom: 0.9em; overflow: hidden;
border-radius: 8px; will-change: transform;">
<iframe loading="lazy" style="position: absolute; width: 100%; height: 100%; top: 0; left: 0; border: none; padding: 0;margin: 0;"
src="https://www.canva.com/design/DAGPwEHxHmc/rgweNnQEQmAvRT0KXlshjw/view?embed" allowfullscreen="allowfullscreen" allow="fullscreen">
</iframe>
</div>
### Video
<iframe width="100%" height="480px" style="border:0;" scrolling="no" src="https://go.screenpal.com/player/cYQhrBHyBA?width=100%&height=100%&ff=1&title=0" allowfullscreen="true"></iframe>
## Sources
https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf
### Related
---
Return [[Home|Home]] | [[SI units]] | [[Uncertainty]] | [[Notes Vault/Physics Notes Vault/Measurements/Dimensional Analysis/Dimensional Analysis|Dimensional Analysis]] | [[Notes Vault/Physics Notes Vault/Measurements/Graphing/Graphing|Graphing]]