PHYSICAL QUANTITIES AND UNITS 1. SI system of units The word physics comes from the Greek word physis which mens nture. When describing things we hve to gree on some terms in order to understnd ech other. Physicl sttes, processes nd their chnges we re ble to mesure re clled physicl quntities. To mesure some quntity mens to compre its vlue with some unit. Ech physicl quntity must hve some numericl mgnitude (vlue) nd unit so tht we know by how much it is bigger or smller thn its unit. A mss equl to five kilogrms cn be written like where m m = 5 kg is the symbol of the physicl quntity of the mss { m } = 5 is the numericl mgnitude of the mss of the object [ m ] = kg is the unit of mss kilogrm SI system of units is the interntionl system now used by the scientists in the whole world. ) Bsic units UNIT SYMBOL QUANTITY metre m length, distnce,... kilogrm kg mss second s time mpére A electric current kelvin K temperture mole mol mount of substnce cndel cd luminous intensity b) Derived units Units derived from the bsic ones using equtions, e.g.: s s 1 v = [ v ] = = m s... combined nme t t F F p = [ p] = = N m 2 = P... specific nme A A Derived units re s well rdin (plnr ngle) nd sterdin (spce ngle). They cnnot be represented s product of some bsic units s we will mention lter. - 1 - PHYSICAL QUANTITIES AND UNITS
c) Multiples nd submultiples stndrd prefix nme symbol multiple ter T 10 12 gig G 10 9 meg M 10 6 kilo k 10 3 milli m 10-3 micro µ 10-6 nno n 10-9 piko p 10-12 2. Sclr nd vector quntities Sclr quntities or sclrs re determined by their numericl mgnitude nd unit only. Exmples re time, length, density, temperture, speed, work, energy, electric current,... To determine vector quntities or vectors the mgnitude nd unit is not enough, we hve to know their direction s well. Exmples re velocity, ccelertion, force, moment of force, momentum, mgnetic flux density, electric nd mgnetic field strength,... To emphsise the vector nture of the quntity we use either bold letters or rrows bove v or v. Size of the vector v = v Vectors cn be connected with certin point (velocity in certin point of the curved trjectory), line of ction (force cting on rigid body) or they cn be even free (moment of couple of forces). Vectors in mths (geometricl) differ from the physicl vectors. 1. Add 3 vectors: x = + b + 2c c b - 2 - PHYSICAL QUANTITIES AND UNITS
2. Find vector z = 2 + b/2 b 3. Subtrct vectors: y = b 3 b 4. Resolve the given vector into two perpendiculr components F 1, F 2. Express these components using the mgnitude of the originl vector nd trigonometric functions of n ngle included. F 5. Add vectors: x = 2 + 3b b b - 3 - PHYSICAL QUANTITIES AND UNITS
I N V E S T I C E D O R O Z V O J E V Z D Ě L Á V Á N Í 6. Resolve vector into given directions: 3. Physicl mesurements Length cn be mesured using simple equipment like ruler or some more ccurte specilised devices like vernier cllipers or micrometer screw guge. http://kbinet.fyzik.net/diln/prezentce/vyukove-prezentce.php Vernier cllipers Micrometer screw guge Wht is the length mesured? -4- PHYSICAL QUANTITIES AND UNITS
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School yer: Gymnázium Olomouc-Hejčín Clss: Dte: Nme: Bsic Mesurements Report No. Techer s signture: Coopertor: Tsk: Compre the precision of vernier cllipers nd micrometer screw guge Equipment: Method: Results: 1) Vernier cllipers No. l/cm l/cm 1 2 3 4 5 6 7 8 9 10 Arithmetic men: = Possible error l = (p.e. = průměrná bs. odchylk) Percentge possible error δl = (p.p.e. = reltivní odchylk) Result: l = ( ± ) cm, δl = % - 1 - PHYSICAL QUANTITIES AND UNITS
2) Micrometer screw guge No. d 0 /mm d 0 /mm d 1 /mm d 1 /mm 1 2 3 4 5 6 7 8 9 10 Arithmetic men: = Arithmetic men: = p.e. d 0 = p.e. d 1 = Arithmetic men: = p.e. d = d 0 + d 1 Result: d = ( ± ) mm, δd = % Conclusion: - 2 - PHYSICAL QUANTITIES AND UNITS