dimensions and units

1.1 Physical Quantities • Most observation in physics are quantitative: distance, speed, energy, time, force …… • Descriptive observations (or qualitative) are usually imprecise. Qualitative Observations How do you measure artistic beauty? Quantitative Observations What can be measured when a car run over speed limit? Quantitative versus qualitative

Chapter Dimensions and units 1.1 Physical Quantities Quantitative versus qualitative • • Most observation in physics are quantitative: distance, speed, energy, time, force …… Descriptive observations (or qualitative) are usually imprecise Qualitative Observations How you measure artistic beauty? Quantitative Observations What can be measured when a car run over speed limit? 1.1 Physical Quantities • A physical quantity is one that can be measured and consists of a magnitude and Vehicles unit  Not 70 Exceeding 4.5 m km/h  SI units are common today 1500 kg In Unladen Weight 1.1 Physical Quantities • Are classified into two types: • • Base quantities Derived quantities Base quantity is like the brick – the basic building block of a house Derived quantity is like the house that was build up from a collection of bricks (basic quantity) 1.2 SI Units • SI Units – International System of Units Base Quantities Name of Unit Symbol of Unit length metre m mass kilogram kg time electric current temperature amount of substance luminous intensity second ampere kelvin mole candela s A K mol cd SI Length Unit: Meter • • • • French Revolution Definition, 1792 Meter = XY/10,000,000 Meter = about 3.28 ft km = 1000 m, cm = 1/100 m, mm = 1/1000 m • Current Definition of Meter: the distance traveled by light in vacuum during a time of 1/299,792,458 second SI Time Unit: Second • Second is defined in terms of an “atomic clock”– time taken for 9,192,631,770 oscillations of the light emitted by a 133Cs atom SI Mass Unit: Kilogram • Kilogram – the mass of a specific platinum-iridium alloy kept at International Bureau of Weights and Measures near Paris (Seeking more accurate measure: http://www.economist.com/ne ws/leaders/21569417kilogram-it-seems-no-longerkilogram-paris-worth-mass) • Copies are kept in many other 1.2 SI Units Derived quantities 1.2 SI Units Derived quantities Derived units (examples) Quantity unit Symbol Volume cubic meter m3 Density kilograms per cubic meter kg/m3 Speed meter per second m/s Newton kg m/ s2 N Energy Joule (kg m2/s2) J Pressure Pascal (kg/(ms2) Pa 1.3 Prefixes • Prefixes simplify the writing of very large or very small quantities Prefix Abbreviation Power nano n 10−9 micro milli centi deci kilo mega giga  m c d k M G 10−6 10−3 10−2 10−1 103 106 109 1.3 Prefixes Scientific Notation M x 10n • • • • M is the coefficient 1[...]... Unit System • We will use SI units in this course, but it is useful to know conversions between systems – 1 mile = 1609 m = 1.609 km 1 ft = 0.3048 m = 30.48 cm – 1 m = 39.37 in = 3.281 ft 1 in = 0.0254 m = 2.54 cm – 1 lb = 0.465 kg 1 oz = 28.35 g 1 slug = 14.59 kg – 1 day = 24 hours = 24 * 60 minutes = 24 * 60 * 60 seconds 1.4 Measurement of Length • The table shows the range and precision of some measuring... Vernier Calipers • The reading shown is 3.15 cm • The instrument also has inside jaws for measuring internal diameters of tubes and containers • The rod at the end is used to measure depth of containers Micrometer Screw Gauge • To measure diameter of fine wires, thickness of paper and small lengths, a micrometer screw gauge is used Micrometer Screw Gauge • The micrometer has two scales: • Main scale on... tighten thimble too much, modern micrometers have a ratchet to avoid this • 2 Clean the ends of the anvil and spindle before making a measurement, any dirt on either of surfaces could affect the reading • 3 Check for zero error by closing the micrometer when there is nothing between the anvil and spindle – The reading should be zero, but it is common to find a small zero error – Correct zero error...Derived units (examples) Quantity unit Symbol Volume cubic meter m3 Density kilograms per cubic meter kg/m3 Speed meter per second m/s Newton kg m/ s2 N Energy Joule (kg m2/s2) J Pressure Pascal (kg/(ms2) Pa 1.3... cm 0.1 cm 0.01 cm 0.01 mm Vernier Calipers • Allows measurements up to 0.01 cm • Consists of a 9 mm long scale divided into 10 divisions Vernier Calipers • The object being measured is between 2.4 cm and 2.5 cm long • The second decimal number is the marking on the vernier scale which coincides with a marking on the main scale Vernier Calipers • Here the eighth marking on the vernier scale coincides