Lesson 1 - Physical Quantities Introduction.docx

[ **Lesson 1 -- PHYSICAL QUANTITIES**] ================================================== **INTRODUCTION:** ================= Measurement is a very important aspect of Physics because the discipline is based on exact measurements. Every such measurement requires two components -- first a number of...

[ **Lesson 1 -- PHYSICAL QUANTITIES**] ================================================== **INTRODUCTION:** ================= Measurement is a very important aspect of Physics because the discipline is based on exact measurements. Every such measurement requires two components -- first a number of quantity and second, a unit to relate the measurements to some standards. Example: 10 meter, 30 seconds, 75 kilograms. A unit or standard of measurement should be such that: 1. It must be possible to define it unambiguously. 2. It must be easily reproducible 3. It does not vary with time and place 4. It should be possible to multiply or divide each one of the standard. **PHYSICAL QUANTITIES** ======================= All measurable attributes, properties or characteristics of objects that can be measured, quantified, or expressed numerically are called **Physical Quantities**. Physical quantities typically have a numerical value and a unit of measurement e.g., 5 meters, 60 seconds, 50 kilograms. Examples of physical quantities include length, mass, time, weight, force, power, speed, acceleration etc **CLASSIFICATION OF PHYSICAL QUANTITIES** Physical quantities can be grouped into two main categories -- **Fundamental and Derived Quantities** [**Fundamental Quantities**: ] These are basic physical quantities that cannot be expressed in terms of other quantities. They are measured directly and not necessarily calculated from a mathematical formular. There are seven (7) of such quantities in physics and they are as follows: a. Length (L): measured in meters (m) b. Mass (M): measured in kilograms (kg) c. Time (T): measured in seconds (s) These are the three most important fundamental quantities. Others are as follows: d. Temperature (θ): measured in kelvins (K) e. Electric Current (I): measured in amperes (A) f. Luminous Intensity: measured in candelas (cd) g. Amount of Substance (n): measured in moles (mol) The units of measurement of the fundamental quantities are called fundamental units. The Systeme International (SI) unit is the most important system of measurement in physics. It used to be called MKS system (metre-kilogram-seconds). Another system previously used is the c.g.s system with centimeter, gram and seconds as standard units of length, time and mass. **[Derived Quantities: ]** These are quantities that can be expressed in terms of fundamental quantities. They are not usually measured directly but are calculated from fundamental quantities using mathematical formulas. Examples include Area, Volume, Density, Speed, Acceleration, etc. **MEASURING INSTRUMENTS** Some essential physical quantities and their respective measuring instruments are as follows: 1. Length: Ruler, Tape measure, Calipers, Micrometer 2. Mass: Balance, Scales, Mass spectrometer 3. Time: Clock, Stopwatch, Timer, Oscilloscope 4. Temperature: Thermometer, Thermocouple 5. Electric Current: Ammeter, Galvanometer 6. Voltage: Voltmeter 7. Resistance: Ohmmeter 8. Pressure: Barometer, Manometer, Pressure gauge 9. Speed: Speedometer, Tachometer, Radar gun 10. Acceleration: Accelerometer 11. Force: Spring balance 12. Energy: Calorimeter