🧪 What Are Physical Quantities?

Physical quantities are things in the real world that we can:

• Observe

• Measure

They describe how much, how far, how fast, how heavy, and how hot, etc.

🧱 Two Types of Physical Quantities:

1. Fundamental (Base) Quantities – The building blocks.

   • Length, Mass, Time, Temperature, Electric current, Amount of substance, Luminous intensity

2. Derived Quantities – Made by combining base ones.

   • Speed = Distance ÷ Time

   • Force = Mass × Acceleration

   • Volume = Length × Width × Height

They all have units. Units tell us what we are measuring and how much.

🎯 Why Do We Measure?

• To compare things scientifically

• To predict outcomes (like force, speed, temperature...)

• To communicate science with exact values

• To design, build, and discover things precisely!

Without measurement, science would just be guesses.

📏 Measurement Techniques :

Let’s see how we measure the real world — with what tools and techniques.

🧍‍♂️1. Measuring Length / Distance

Instruments:

• Ruler (small things)

• Vernier Caliper (very small gaps, like in engineering)

• Micrometer Screw Gauge (tiny parts like wires)

• Laser Rangefinders (long distances)

• Radar / LIDAR (for huge distances or scanning)

  
  

Science Behind It:

• Light waves can bounce back to measure time taken (used in laser/radar).

• Measurement is about comparing the object to a standard unit (like 1 meter).

  
  

⚖️2. Measuring Mass

Instruments:

• Balance scale (compares weight)

• Electronic scale (uses force sensors)

• Spring balance (uses gravity and spring stretching)

  
  

Science Behind It:

• Mass is the amount of matter inside something.

• It never changes, even on the Moon (gravity does not matter ).

  
  

⏱️3. Measuring Time

Instruments:

• Stopwatch / Clock

• Atomic Clock (most accurate – uses vibrations of atoms!)

• Pendulum Clocks (old style – gravity-controlled swing)

• Quartz Clock (uses vibrating crystals)

  
  

Science Behind It:

• Time measurement is about counting repeating cycles (vibrations, swings, pulses).

• Atomic clocks use cesium atoms vibrating billions of times per second — perfect for GPS and science!

  
  

🌡️4. Measuring Temperature

Instruments:

• Thermometer (mercury or alcohol expands with heat)

• Digital sensors (convert temperature to electrical signals)

• Thermocouple (two different metals produce voltage when heated)

• Infrared sensors (detect heat radiation)

  
  

Science Behind It:

• Temperature = how fast molecules are moving

• Heat energy makes particles vibrate more

• Instruments either expand materials or use electricity to detect that movement

  
  

🔋5. Measuring Electric Current & Voltage

Instruments:

• Ammeter (current)

• Voltmeter (voltage)

• Multimeter (does both)

• Oscilloscope (shows changing signals)

  
  

Science Behind It:

• Current = how many electrons flow per second

• Voltage = how much energy each electron carries

• Measuring is done by letting some current pass through known resistors and calculating energy

  
  

🌍6. Measuring Force, Pressure, Energy, Speed, etc. (Derived Quantities)

Examples:

• Speed = distance ÷ time → measured with speed sensors or GPS

• Force = mass × acceleration → measured using spring scales or force sensors

• Pressure = force ÷ area → measured using barometers or pressure gauges

• Energy = measured by calorimeters, electric meters, etc.

These quantities are not basic — we build them using other measurements!

🧠 Standard Units and SI System

We need everyone in the world to agree on what one meter, one kilogram, or one second means.

That’s why we use:

✨ SI Units (Systeme Internationale)

• Meter (m) – Length

• Kilogram (kg) – Mass

• Second (s) – Time

• Kelvin (K) – Temperature

• Ampere (A) – Current

• Mole (mol) – Amount of substance

• Candela (cd) – Brightness

This system keeps science universal and exact.

🧩 Final Summary:

1. Physical quantities describe real-world features like size, mass, time, temperature, etc.

2. We measure using tools that compare things to standard units.

3. Techniques depend on the physics of the tool — expansion, vibration, electricity, gravity, etc.

4. Modern science uses super accurate tools like atomic clocks, lasers, and sensors.

5. Measurement is how we turn the world into numbers — and that’s the base of all science.