Lecture 1: Measurements - Physics & Laser (BAS 111) PDF

Course Title : Physics & Laser Course Code : BAS 111 Department : Physics Lecture 1 Measurements Dr. Yasser Abdou Physics Department @ Alsalam University [email protected]  What is Physics? ❑ Physics is the study of the basic components of the un...

Course Title : Physics & Laser Course Code : BAS 111 Department : Physics Lecture 1 Measurements Dr. Yasser Abdou Physics Department @ Alsalam University [email protected]  What is Physics? ❑ Physics is the study of the basic components of the universe and their interactions. ❑Theories of physics have to be verified by the experimental measurements.  Measurement A scientific measurement requires: (1) the definition of the physical quantity (2) the units. The value of a physical quantity is actually the product of a number and a unit. The precision of the measurement result is determined by procedures used to measure them.  Basic Measurements Length: Our “How far?” question involves being able to measure the distance between two points. Time: To answer the question, “How long did it take?” Mass: Mass is a measure of “amount of stuff (matter).”  The Système International (SI) of units The SI, or metric system of units is the internationally accepted system of units for measurement in all of the sciences, including physics. The SI consists of base units and derived units: (1) The set of base units comprises an irreducible set of units for measuring all physical variables (2) The derived units can be expressed in terms of the base units  Physical Quantities Basic Quantities Derived Quantities The Quantities on Quantities that are the basis of which expressed in other quantities terms of base are expressed. quantities. Physical Quantities The SI Base Units SI Units SI Units Example of derived quantity: area Defining equation: area = length × width In terms of units: Units of area = m × m = m2 Defining equation: volume = length × width × height In terms of units: Units of volume = m × m × m = m3 Defining equation: density = mass ÷ volume In terms of units: Units of density = kg / m3 = kg m−3 SI Units Work out the derived quantities for: distance Defining equation: speed = time In terms of units: Units of speed = velocity Defining equation: acceleration = time In terms of units: Units of acceleration = Defining equation: force = mass × acceleration In terms of units: Units of force = SI Units Work out the derived quantities for: Force Defining equation: Pressure = Area In terms of units: Units of pressure = Defining equation: Work = Force × Displacement In terms of units: Units of work = Work done Defining equation: Power = Time In terms of units: Units of power =  Prefixes Prefixes simplify the writing of very large or very small quantities Prefix Abbreviation Power nano n 10−9 micro  10−6 milli m 10−3 centi c 10−2 deci d 10−1 kilo k 103 mega M 106 giga G 109 Prefixes  Prefixes Alternative writing method Using standard form N × 10n where 1  N < 10 and n is an integer This galaxy is about 2.5 × 106 The diameter of this atom light years from the Earth. is about 1 × 10−10 m. 1. A physical quantity is a quantity that can be measured and consists of a numerical magnitude and a unit. 2. The physical quantities can be classified into base quantities and derived quantities. 3. There are seven base quantities: length, mass, time, current, temperature, amount of substance and luminous intensity. 1. The SI units for length, mass and time are metre, kilogram and second respectively. 2. Prefixes are used to denote very big or very small numbers.  Measurement of Time Time Measured in years, months, days, hours, minutes and seconds SI unit for time is the second (s). Clocks use a process which depends on a regularly repeating motion termed oscillations.  Measurement of Time Time The oscillation of a simple pendulum is an example of a regularly repeating motion. The time for 1 complete oscillation is referred to as the period of the oscillation.  Measurement of Time Pendulum Clock Measures long intervals of time Hours, minutes and seconds Mass at the end of the chain attached to the clock is allowed to fall Gravitational potential energy from descending mass is used to keep the pendulum swinging In clocks that are wound up, this energy is stored in coiled springs as elastic potential energy.  Measurement of Time Watch also used to measure long intervals of time most depend on the vibration of quartz crystals to keep accurate time energy from a battery keeps quartz crystals vibrating some watches also make use of coiled springs to supply the needed energy  Measurement of Time Stopwatch Measure short intervals of time Two types: digital stopwatch, analogue stopwatch Digital stopwatch more accurate as it can measure time in intervals of 0.01 seconds. Analogue stopwatch measures time in intervals of 0.1 seconds.  Density The density (ρ) of a material: is the mass per unit volume. Density of water = 1000 Kg/m3 or 1.0Kg/dm3 1g/cm3 Density Density Density Density Why do icebergs float in the sea ? Why does steel sink in water? Thank you