BASIC ENGINEERING SCIENCE BASIC ENGINEERING SCIENCE OBJECTIVES 1

BASIC ENGINEERING SCIENCE

BASIC ENGINEERING SCIENCE OBJECTIVES 1. Ability to define and understand base and derived quantities, distinguish standard units and system of unit, and fundamental quantities. 2. Ability to understand apply converting units within a system or from one system of unit to another 3. Ability to understand apply Dimensional Analysis.

BASIC ENGINEERING SCIENCE DEFINITION a physical quantity that can be counted or measured using standard size defined by custom or law. Every measurement or quantitative statement requires a unit. Example: If you say you’re driving a car 30 that doesn't mean anything. Are you driving it 30 miles/hour, 30 km/hour, or 30 ft/sec? 30 only means something when unit is attached to it.

BASIC ENGINEERING SCIENCE STANDARD UNITS If a unit becomes officially accepted, it’s called Standard Unit. Group of Unit and Combination is called SYSTEM OF UNITS. Example: SI Units, British Units SI = International Systems of Units

BASIC ENGINEERING SCIENCE PHYSICAL QUANTITIES - Physics is based on physical quantities. Eg: length, mass, time, force and pressure. - Generally, physical quantity is a quantity that can be measured. Physical quantities Definition Base quantities Fundamental quantities having their own dimensions. Eg: length, mass, time, electrical current, etc. Derived quantities The quantity which derived from base quantity. Eg: force, energy, pressure, etc

BASIC ENGINEERING SCIENCE BASE QUANTITIES IN SI SYSTEM Name Symbol of quantity Symbol of dimension SI base unit Length l L meter (m) Time t T second (s) Mass m M kilogram (kg) Electrical current I I Ampere (A) Thermodynami c temperature T Kelvin (K) Amount of substance n N mole Luminous intensity Iv J Candela (c)

BASIC ENGINEERING SCIENCE DERIVED QUANTITIES FROM BASE QUANTITIES Quantity Name Symbol of quantity SI unit Symbol of dimension Force, Weight Newton N mkg/s 2 LMT-2 Energy, Work, Heat Joule J m 2 kg/s 2 L 2 MT-2 Power, radian flux Watt W m 2 kg/s 3 L 2 MT-3 Frequency Hertz Hz s-1 T-1 Pressure, Stress Pascal Pa m-1 kg/s 2 L-1 MT-2 Electric charge or flux Coulomb C As AT Electrical potential difference Volt V m 2∙kg∙s− 3∙A− 1 L 2 MT-3 A-1

BASIC ENGINEERING SCIENCE Quantity Name Symbol of quantity SI unit Symbol of dimension Electric resistance, Impedance, Reactance Ohm Ω m 2 kgs− 3 A− 2 L 2 MT-3 A-2 Electric capacitance Farad F m− 2 kg− 1 s 4 A 2 L-2 M-1 T 4 A 2 Magnetic flux density, magnetic induction Tesla T kgs− 2 A− 1 MT-2 A-1 Magnetic flux Weber W m 2 kgs− 2 A− 1 L 2 MT-2 A-1 Inductance Henry H m 2 kgs− 2 A− 2 L 2 MT-2 A-2

BASIC ENGINEERING SCIENCE CONVERSION FACTORS • To change units in different systems, or different units in the same system. SI to C. G. S. to SI 1 m = 100 cm 1 cm = 10 -2 m 1 kg = 1000 g 1 g = 10 -3 kg 1 m 2 = 104 cm 2 1 cm 2 = 10 -4 m 2 1 m 3 = 106 cm 3 1 cm 3 = 10 -6 m 3 Example 1: Convert Density of water which is 1 g cm-3 to SI unit

BASIC ENGINEERING SCIENCE Example 2 • A hall bulletin board has an area of 2. 5 m 2. What is area in cm 2? Solution:

BASIC ENGINEERING SCIENCE Example 3 • Convert miles per hour to meters per second. Given: – 1 inch = 2. 54 cm – 1 m = 3. 28 ft – 1 mile = 5280 ft – 1 mile = 1. 61 km

BASIC ENGINEERING SCIENCE DIMENSION From Latin word = "measured out" • a parameter or measurement required to define the characteristics of an object • The dimension of physical quantity relates the physical quantity to base quantities such as mass(M), length(L), time (T), electric current (I) and temperature (θ).

BASIC ENGINEERING SCIENCE The dimension of a physical quantity can be written as [physical quantity] Unit for velocity is ms-1 Unit force is kg ms-2 or N Unit for frequency is s-1 or Hz

BASIC ENGINEERING SCIENCE DIMENSIONAL ANALYSIS PURPOSES: 1) to check the homogeneity of physical equations Example (to check homogeneity ): Example (to check Distance, d=vt 2 ( velocity x time 2 ) Dimension on left side [d] = L Dimension on right side [vt 2] = L / T x T 2 = L x T L=LT? Left units and right units don’t match, the equation must be wrong !!

BASIC ENGINEERING SCIENCE Example 4 • The force (F) to keep an object moving in a circle can be described in terms of the velocity, v, (dimension L/T) of the object, its mass, m, (dimension M), and the radius of the circle, R, (dimension L). – Which of the following formulas for F could be correct ? (a) F = mv. R (b) Remember: Force has dimensions of ML/T 2 (c)

BASIC ENGINEERING SCIENCE Solution (a) F = mv. R (b) (c)

BASIC ENGINEERING SCIENCE Exercise Show the dimensions of the following equations are homogeneous a) b) c) d) Impulse, Ft=m(v-u) Pressure, p =hρg Kinetic energy, Period,

BASIC ENGINEERING SCIENCE Solution

BASIC ENGINEERING SCIENCE END OF CHAPTER 1