Physical Quantities Master Table
A dynamic reference of over 50+ physical quantities. Search by name, symbol, or dimensions.
| Quantity | Symbol | SI Unit | Dimension | Type |
|---|---|---|---|---|
Length Fundamental | l, x, r | meterm | Scalar | |
Mass Fundamental | m | kilogramkg | Scalar | |
Time Fundamental | t | seconds | Scalar | |
Electric Current Fundamental | I, i | ampereA | Scalar | |
Thermodynamic Temperature Fundamental | T, Θ | kelvinK | Scalar | |
Amount of Substance Fundamental | n | molemol | Scalar | |
Luminous Intensity Fundamental | Iv | candelacd | Scalar | |
Area Mechanics | A | square meterm² | Scalar | |
Volume Mechanics | V | cubic meterm³ | Scalar | |
Density Mechanics | ρ | kilogram per cubic meterkg/m³ | Scalar | |
Speed / Velocity Mechanics | v | meter per secondm/s | Vector | |
Acceleration Mechanics | a | meter per second squaredm/s² | Vector | |
Momentum Mechanics | p | kilogram meter per secondkg·m/s | Vector | |
Force Mechanics | F | newtonN | Vector | |
Impulse Mechanics | J | newton secondN·s | Vector | |
Work / Energy Mechanics | W, E | jouleJ | Scalar | |
Power Mechanics | P | wattW | Scalar | |
Pressure Mechanics | p | pascalPa | Scalar | |
Torque Mechanics | τ | newton meterN·m | Vector | |
Surface Tension Mechanics | γ | newton per meterN/m | Scalar | |
Viscosity (Dynamic) Mechanics | η | pascal secondPa·s | Scalar | |
Moment of Inertia Mechanics | I | kilogram square meterkg·m² | Scalar | |
Electric Charge Electricity | Q, q | coulombC | Scalar | |
Electric Potential (Voltage) Electricity | V | voltV | Scalar | |
Capacitance Electricity | C | faradF | Scalar | |
Electrical Resistance Electricity | R | ohmΩ | Scalar | |
Conductance Electricity | G | siemensS | Scalar | |
Magnetic Flux Electricity | Φ | weberWb | Scalar | |
Magnetic Field Strength Electricity | B | teslaT | Vector | |
Inductance Electricity | L | henryH | Scalar | |
Frequency General | f, ν | hertzHz | Scalar | |
Entropy Heat | S | joule per kelvinJ/K | Scalar | |
Specific Heat Capacity Heat | c | joule per kilogram kelvinJ/(kg·K) | Scalar | |
Thermal Conductivity Heat | k | watt per meter kelvinW/(m·K) | Scalar | |
Luminous Flux Light | Φv | lumenlm | Scalar | |
Illuminance Light | Ev | luxlx | Scalar | |
Radioactivity Atomic | A | becquerelBq | Scalar | |
Absorbed Dose Atomic | D | grayGy | Scalar | |
Catalytic Activity Chemistry | - | katalkat | Scalar | |
Angle (Plane) General | θ | radianrad | Scalar | |
Solid Angle General | Ω | steradiansr | Scalar |
Showing 41 quantities
Mastering Physics: The Language of Measurement
In the vast world of Physics, implies nothing without measurement. To understand the universe, from the motion of galaxies to the vibration of atoms, we need a standard way to measure and communicate. This is where Physical Quantities and SI Units come into play. A physical quantity is any property of matter or energy that can be measured and expressed in numbers, such as mass, time, or velocity.
Scalar Quantities
These are the "simple" quantities. They have only magnitude (size) and no direction.
- Mass (5 kg)
- Time (30 seconds)
- Volume (2 liters)
Vector Quantities
These quantities are direction-dependent. They have both magnitude AND direction.
- Force (10N downwards)
- Velocity (50 km/h North)
- Displacement
Fundamental vs. Derived Quantities
Physics is built on a hierarchy. At the base, we have the 7 Fundamental Quantities. These are independent and cannot be defined in terms of other quantities. Every other quantity in existence (called Derived Quantities) is just a mathematical combination of these seven base pillars.
For example, Speed is not fundamental. It is derived from Length divided by Time ($L/T$). Force is even more complex, combining Mass, Length, and Time ($ML/T^2$).
Why Dimensional Analysis Matters?
Dimensional Analysis is a powerful tool used by physicists to check if equations make sense. We refer to the dimension of Mass as [M], Length as [L], and Time as [T].
💡 The Golden Rule of Physics
"You cannot add apples to oranges." In physics terms, you can only add or subtract quantities that have the exact same dimensions. You can add 5 meters to 2 meters, but you cannot add 5 meters to 2 seconds.
Evolution of Unit Systems
Before the world agreed on a standard, chaos reigned. Different regions used different systems:
- CGS System (French): Centimeter, Gram, Second. Good for small scale lab work but inconvenient for large engineering.
- FPS System (British): Foot, Pound, Second. Still used in the US and some engineering fields, but clumsy for calculation (12 inches = 1 foot?).
- MKS System: Meter, Kilogram, Second. The direct ancestor of our modern SI units.
- SI System (Modern): Système International. Adopted globally in 1960. It covers all fields including Thermodynamics and Electricity (using Kelvin and Ampere).
Frequently Asked Questions
What are the 7 Fundamental Physical Quantities?
The 7 fundamental quantities defined by the SI system are: Length (meter), Mass (kilogram), Time (second), Electric Current (ampere), Thermodynamic Temperature (kelvin), Amount of Substance (mole), and Luminous Intensity (candela). All other quantities are derived from these seven.
What is the specific difference between Scalar and Vector quantities?
Scalar quantities have only magnitude (size) but no direction (e.g., Mass, Time, Temperature). Vector quantities have both magnitude and direction and obey the laws of vector addition (e.g., Force, Velocity, Displacement).
Why is "Radian" considered a supplementary unit?
Plane Angle (radian) and Solid Angle (steradian) are considered dimensionless derived quantities (formerly supplementary). They have units but no dimensions because they are ratios of lengths (Arc/Radius).
Can a quantity have units but no dimensions?
Yes. Angles are the classic example. They are measured in degrees or radians (units) but are dimensionless numbers ([M⁰L⁰T⁰]) because they represent a ratio of two lengths.
Can a quantity have dimensions but no unit?
No, looking at standard physics, this is impossible. If a physical quantity has a dimension (like [L] or [T]), it must be measurable in some unit (like meters or seconds).
What is the Principle of Homogeneity of Dimensions?
This principle states that for any correct physical equation, the dimensions of all terms on both sides of the equality must be identical. You can only add or subtract quantities that have the exact same dimensions.
Why do we prefer SI units over CGS or FPS?
SI (System International) is a "coherent" system, meaning derived units are obtained by simple multiplication or division without numerical factors. It is also metric (decimal-based), making conversions simple, unlike the FPS (Foot-Pound-Second) system.
How do you find the dimension of a constant like "G" (Gravitational Constant)?
Use the formula: F = G(m₁m₂)/r². Rearrange for G: G = Fr²/(m₁m₂). Substitute dimensions: [MLT⁻²][L²] / [M][M] = [M⁻¹L³T⁻²].
Are all constants dimensionless?
No. Some constants like Pi (π) or Euler's number (e) are dimensionless. However, physical constants like Planck's constant (h), Gravitational constant (G), and Speed of light (c) definitely have dimensions and units.
What is Dimensional Analysis used for?
It is used to: 1) Check the correctness of a physical equation. 2) Derive relationships between different physical quantities. 3) Convert the value of a quantity from one system of units to another.