Presentation on theme: "Safe Hands, Akola Mechanics and properties of matter Measurements By: Dr. Nitin Oke."— Presentation transcript:
Safe Hands, Akola Mechanics and properties of matter Measurements By: Dr. Nitin Oke.
Safe Hands, Akola Need of measurement Physical theory need experimental verification and results of experimental verification involves measurement. If every one decide to have his own way of measurement then it will not be possible to come to correct conclusion. Thus a well defined, universally accepted system must be developed
Safe Hands, Akola Need of system of units It must be convenient Easily reproducible Must be uniform and constant Internationally accepted.
Safe Hands, Akola Different systems of units FPS system: Used by Europeans, consist of three basic units for length, mass and time. The units were foot (ft), pound (lb) and for time it is second (s). Metric system: MKSA system, it is system based on quantities for length, mass, time and current. Sub system of this system is more popular by name MKS. SI system: Recent mostly accepted. It is abbreviation of ”System International de unites” (1960) It consist of six base units two supplementary units and derived units.
Safe Hands, Akola SI system Base units are –Meter : it is defined as times the wavelength in vacuum of orange red line emitted by krypton 86. –Present definition is length of path traveled by light in vacuum during time interval 1/ of second. –Kilogram : It is the mass of prototype of iridium – platinum alloy kept in “ International Bureau of Weights and measures at serves, Near Paris in France –Second : It is the time taken by radiation from cesium- 133 atom to complete vibrations
Safe Hands, Akola SI system Base units are –Ampere : it is defined as current flowing through each of two thin parallel conductors of infinite length kept in free space at a distance of a meter apart, produces a force of 2 x N per unit length. –Candela : It is the luminous intensity of an area of 1/ m2 m2 of black body in the normal direction to its surface at temperature of freezing platinum under the pressure of N/m 2 –Kelvin : It is the fraction 1/ of thermodynamic temperature of triple point of water. –Mole : It is defined as the amount of substance of a system which the same number of elementary entities as there are atoms in exactly 12 grams of pure carbon 12
Safe Hands, Akola Supplementary units are –Radian : It is the angle subtended by an arc length equal to radius of a circle at centre of circle. –Steradian : It is the solid angle subtended at the centre of a sphere by an area of a square on the surface of a sphere each side of square is of length equal to radius of sphere. SI system
Safe Hands, Akola Fundamental physical quantities Fundamental physical quantities: The physical quantities which can not be expressed in terms of other physical quantities are called as fundamental physical quantities. Fundamental physical quantities: The physical quantities which are chosen for base units are called as fundamental physical quantities. Fundamental units: Units expressing fundamental quantities is called as fundamental units.
Safe Hands, Akola Derived physical quantities Physical quantities which can be expressed in terms of one or more fundamental quantities are called as derived quantities. –Speed, acceleration, density, volume, force, momentum, pressure, room temperature. charge, potential difference, KE, PE, resistance, work,
Safe Hands, Akola Derived physical quantities –Speedlength/timem/s –Accelerationlength/time 2 m/s 2 –Densitymass/ length 3 kg/m 3 –Volumelength 3 m 3 –Forcemass.(length)/time 2 kg.m/s 2 –Momentummass. Length/time kg. m/s –Pressure mass/length.time 2 kg/ms 2 –room temperature temperatureK
Safe Hands, Akola Short recall Force = mass. displacement Work = force. Displacement KE = ½ mv 2 PE = m. g. h I = charge/time pd = energy required to circulate the unit charge from terminal to terminal. = E/q R = V/I
Safe Hands, Akola Derived physical quantities –Charge = current x Time = A.s –Work= force. Displacement = mass x (length) 2 /(time) 2 –KE = mass x (length) 2 /(time) 2 –PE= mass x (length) 2 /(time) 2 –potential difference = energy per unit charge = [mass x (length) 2 /(time) 2 ] /current. time = mass x (length) 2 /current. time 3 –Resistance –= V/ I = (M.L 2 /I.T 3 )/I = ML 2 /I 2 T 3
Safe Hands, Akola More about Units Fundamental Quantities SI UnitsSymbol Lengthmeterm Masskilogramkg Timeseconds Electric current ampereA Luminous intensity candelacd TemperaturekelvinK Molemolemol
Safe Hands, Akola More about Units Derived Quantities SI UnitsSymbol ForcenewtonN Work / EnergyjouleJ PowerwattW Electric chargecoulombC potentialvoltV resistanceohmΩ frequencyhertzHz
Safe Hands, Akola Always remember Full names of units are NOT written starting with capital initial letter. Meter meter K ilogram kilogram N ewton newton Units named after person will NOT be written with capital initial letter. The symbol of the units in memory of a person will be in capital letters. This will not be for other units. newton N n kilogram Kg kg
Safe Hands, Akola Dimensional Analysis Dimensions of a physical quantity are the powers to which the fundamental units must be raised in order to get the unit of derived quantity. –Symbols used for fundamental quantities are –Length [ L ], mass [ M ], time [ T ], current [I], Temperature [ ] –Using powers of these symbol we represent dimension of physical quantities. In short the dimension is expression which shows the relation between the derived unit and the fundamental units.
Safe Hands, Akola Dimensions of derived units [T -1 ]frequency [L 1 T -1 ]speed [L 1 T -2 ]acceleration [M 1 L 1 T -1 ]momentum [M 1 L 1 T -2 ]Force [M 1 L 2 T -3 ]Power [M 1 L 2 T -2 ] Work/ Energy dimension Derived Quantities [IT] Electric charge [M 1 L 1 T -3 I -1 ]potential [M 1 L 1 T -3 I -2 ] resistance [ ] Radian, refractive index etc [M 1 L -3 ]Density dimension Derived Quantities
Safe Hands, Akola Application of dimensional equation Dimensional analysis can be used — 1.to check whether the given equation is dimensionally correct. ( If an equation is dimensionally correct then it can differ only in numerical constants.) 2.To find the relation between same unit in different systems. For example let 1N = dyne 1[M 1 L 1 T -2 ] = [M 1 L 1 T -2 ] kg.m.s -2 = gm.cm.s -2
Safe Hands, Akola Significant figure Order of magnitude: If a number is expressed as “n x 10 m ” where 0.5 ≤ n < 5 then 10 m is called as order of magnitude. Significant figure: –Reliable figure : –Doubtful figure:
Safe Hands, Akola Significant figure Significant figure: The number of all nonzero digits are significant. –234 has 3 significant digits – has 8 significant digits Decimal point is a problem as If number is free of decimal point then zero on right of first nonzero digit are NOT significant means –200has 1 significant digit –3700has 2 significant digits If number is with decimal point then zeros to the right of decimal point and on left of first nonzero number is non significant but zeros on right of last nonzero digit are significant –0.0102has 3 significant digits –0.0120has 3 significant digits –0.00has 2 significant digit – has 2 significant digits
Safe Hands, Akola Need and notation of scientific numbers If reading is 2.320m = 232.0cm = 2320mm = km Here 2320mm has 3 significant digits and has 4 significant digits To avoid above contradiction we use scientific notation in which the number will be written as –2.320m = x 10 2 cm = x 10 3 mm = x km As power of ten does not contribute in significant figures thus even by changing units the number of significant digits will remain same.
Safe Hands, Akola Operation with scientific figures During addition or subtraction always express answer with number of digits after decimal point is same as the number with the least number of digits after decimal point. For example