Physics and Physical Measurement The Realm of physics Measurement and uncertainties

The Realm of Physics Range of magnitudes of quantities in our universe: – Visible universe= m – The age of the universe= s – The total mass of the universe= kg The atom: – The diameter of an atom = m – The diameter of the nucleus = m

Upper and lower measurements Planck length m (lower) Speed of light in a vacuum 3 x10 8 m/s Time = distance/ speed – Time= m/ 10 8 m/s – Time= s If quarks are the fundamental unit then their mass would give us the lower limit, but they hide in protons and our best guess is kg. This is also the approximate mass of an electron at rest.

Stating ratios as differences in magnitude m/ m= is known as a difference of five orders of magnitude. What is the order of magnitude of the diameter of a proton? A mB m C m

Estimating Approximate Values Estimate the value of these everyday quantities to one or two significant figures. – How high is a two storey house in meters? – What is the diameter of your pupil? – How many times does your heart beat in an hour when you are relaxed? – What is the weight of an apple in Newtons?

Fundamental Units Metermlength Kilogramkgmass Secondstime AmpereAelectric current KelvinKtemperature Molemolamount of matter Candelacdintensity of light

Mechanics and Derived Units Mechanics is the study of matter, forces, and energy. With combinations of the first three base units (m, kg, and s), all other units for mechanics can be developed. NewtonNforce or weight kg m s -2 JouleJenergy or work kg m 2 s -2 WattWpower kg m 2 s -3 PascalPapressure kg m -1 s -2

Derived Units Find the symbol, concept, and broken down base units for each of the following: Hertz Coulumb Ohm Tesla Weber Becquerel

Problems 1.Give units for the following expressed as derived and base units: a.Forceb. Kinetic energy 2.Check if these equations work by substituting units into them. a.Power= work/time or energy/time b.Power = force x velocity

Answers 1. a. N or kg m s -2 b.J or kg m 2 s a. W: J s -1 or W: (kg m 2 s -2 )s -1 or W: kg m 2 s -3 b. W: N x (m s -1 ) or W: (kg m s -2 )x (m s -1 ) or W: kg m 2 s -3

Problems 3. Which one of the following units is a unit of energy? a. eVb. W s -1 c. W m -1 d. N m s Which on of the following lists a derived unit and a fundamental unit? AAmpereSecond BCoulombKilogram CCoulombNewton DMeterkilogram

Answers 3.eV 4.B

Other Units NameSymbolConcept LiterLvolume Minute, hour, year, etc.Min, h, y, etc.Time Kilowatt-hourkWhEnergy ElectronvolteVEnergy Degrees celsius oCoCtemperature DecibeldBLoudness Unified atomic mass unitUMass of nucleon

Problem 5.Convert these units to SI: a. Yearb. 100 o C c. kWhd. eV

Modifying SI Units SI units can be modified by the use of prefixes. PrefixAbbreviationValue TeraT10 12 GigaG10 9 MegaM10 6 Kilok10 3 centic10 -2 millim10 -3 microμ10 -6 nanon10 -9 picop femtof10 -15

Problems 6.Change J to scientific notation and MJ. 7.A popular radio station has a frequency of Hz. Change this to scientific notation and MHz. 8.The average wavelength of white light is 5.0x m. What would this be in nanometers? 9. The time taken for light to cross a room is about 1 x10 -8 s. Change this into microseconds.

Answers x 10 6 J or 2.36 MJ x 10 6 Hz or 1.09 MHz nm μs

Uncertainty and Error There are two types of errors: Random and systematic Random errors can be reduced by repeating measurement many times. Systematic errors can be reduced by repeating measurement using a different method or different apparatus and comparing the results.