1. Units and Measurement Physics Mrs. Coyle International Space Station http://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg

2. It All Starts with a Ruler!!!

3. Introduction to physics Definition of physics Physics is one of the branches of natural sciences and studies about all phenomena in such away that to find energy from matters which are found in the universe. The word of physic is derived from a Greek word meaning nature nature.

4. Aims of physics The following are aims of physic Seeking natural laws and understanding them Exploring the interaction between matter and energy

5. Branches of physics The study of physics can be divided into six main areas: 1. Classical mechanics, concerning the motion of objects that are large relative to atoms and move at speeds much slower than the speed of light; 2. Relativity, a theory describing objects moving at any speed, even speeds approaching the speed of light; 3. Thermodynamics, dealing with heat, work, temperature, and the statistical behavior of systems with large numbers of particles

6. cont… 4. Electromagnetism, concerned with electricity, magnetism, and electromagnetic fields; 5. Optics, the study of the behavior of light and its interaction with materials; 6. Quantum mechanics, a collection of theories connecting the behavior of matter at the submicroscopic level to macroscopic observations.

7. Physic and measurements Like all other sciences, physics is based on experimental observations and quantitative measurements. The main objectives of physics are to identify a limited number of fundamental laws that govern natural phenomena and use them to develop theories that can predict the results of future experiments. The fundamental laws used in developing theories are expressed in the language of mathematics, the tool that provides a bridge between theory and experiment.

8. Standards of length, mass, and time To describe natural phenomena, we must make measurements of various aspects of nature. Each measurement is associated with a physical quantity, such as the length of an object. In 1960, an international committee established a set of standards for the fundamental quantities of science. It is called the SI (System International), and its fundamental units of length, mass, and time are the meter, kilogram, and second, respectively. Other standards for SI fundamental units established by the committee are those for temperature (the kelvin), electric current (the ampere), luminous intensity (the candela), and the amount of substance (the mole).

9. Length We can identify length as the distance between two points in space. In 1120, the king of England decreed that the standard of length in his country would be named the yard and would be precisely equal to the distance from the tip of his nose to the end of his outstretched arm as recently as 1960, the length of the meter was defined as the distance between two lines on a specific platinum–iridium bar stored under controlled conditions in France.

10. Cont… In October,1983, however, the meter was redefined as the distance traveled by light in vacuum during a time of 1/299 792 458 second. In effect, this latest definition establishes that the speed of light in vacuum is precisely 299 792 458 meters per second. This definition of the meter is valid throughout the Universe based on our assumption that light is the same everywhere.

11. Mass The SI fundamental unit of mass, the kilogram (kg), is defined as the mass of a specific platinum–iridium alloy cylinder kept at the International Bureau of Weights and Measures at Sevres, France. This mass standard was established in 1887 and has not been changed since that time because platinum–iridium is an unusually stable alloy.

12. Time Before 1960, the standard of time was defined in terms of the mean solar day for the year 1900. (A solar day is the time interval between successive appearances of the Sun at the highest point it reaches in the sky each day.). The fundamental unit of a second (s) was defined as (1/60)(1/60)(1/24) of a mean solar day. In addition to SI, another system of units, the U.S. customary system, is still used in the United States despite acceptance of SI by the rest of the world.

13. Math and Units Math- the language of Physics SI Units – International System – MKS Meter m Mass kg Time s National Bureau of Standards Prefixes

14. SI Unit Prefixes - Part I NameSymbolFactor tera-T10 12 giga-G10 9 mega-M10 6 kilo-k10 3 hecto-h10 2 deka-da10 1

15. SI Unit Prefixes- Part II NameSymbolFactor deci-d10 -1 centi-c10 -2 milli-m10 -3 micro-μ10 -6 nano-n10 -9 pico-p10 -12 femto-f10 -15

16. The Seven Base SI Units QuantityUnitSymbol Lengthmeterm Masskilogramkg TemperaturekelvinK Timeseconds Amount of Substance molemol Luminous Intensitycandelacd Electric Currentamperea

17. Derived SI Units (examples) QuantityunitSymbol Volumecubic meterm3m3 Densitykilograms per cubic meter kg/m 3 Speedmeter per secondm/s Newtonkg m/ s 2 N EnergyJoule (kg m 2 /s 2 )J PressurePascal (kg/(ms 2 )Pa

18. SI Unit Prefixes for Length NameSymbolAnalogy gigameterGm10 9 megameterMm10 6 kilometerkm10 3 decimeterdm10 -1 centimetercm10 -2 millimetermm10 -3 micrometerμmμm10 -6 nanometernm10 -9 picometerpm10 -12

19. Formulas The variables length, time, and mass are examples of fundamental quantities. Most other variables are derived quantities, those that can be expressed as a mathematical combination of fundamental quantities. Common examples are area (a product of two lengths) and speed (a ratio of a length to a time interval). Another example of a derived quantity is density. The density p (Greek letter rho) of any substance is defined as its mass per unit volume: P = m/v

20. formulas Volume = m/p Volume of cylinder = πr 2 h = Ah where A = πr 2 Volume of sphere = 4/3 πr 3

21. Example If The standard kilogram is a platinum-iridium cylinder 29 mm in height and 29 mm in diameter. What is the density of the material?

22. Solution h= 29mm, r = 14.5mm m = 1kg V = π r 2 h = (3.14)(14.5) 2 (29) ≈ 19145 = 1.9145 x 10 4 mm 3 1.9145 x 10 4 mm 3 ≈ 1.9 x 10 -5 m 3 Density (p) = m/v = 1kg/ 1.9 x 10 -5 m 3 P = 5.2 x 10 4 kg/m 3.

23. Scientific Notation M x 10 n M is the coefficient 1<M<10 10 is the base n is the exponent or power of 10

24. Other Examples: 5.45E+6 or 5.45 x 10^6

25. Numbers less than 1 will have a negative exponent. A millionth of a second is: 0.000001 sec 1x10 -6 1.0E-6 1.0^-6

26. Conversion of Units Sometimes you must convert units from one measurement system to another or convert within a system (for example, from kilometers to meters). Equalities between SI and U.S. customary units of length are as follows:

27. Cont… 1mile = 1609m = 1.609km 1m = 39.37in = 3.281ft 1ft = 0.3048m = 30.48cm 1in = 0.025m = 2.54cm 1gal = 3.786L 1m ≈ 1yd 1kg ≈ 2Ib

28. Example

29. Cont…

30. Example: Convert 5km to m: Multiply the original measurement by a conversion factor. NEW UNIT 85km x 1,000m = 85,000m 1km OLD UNIT

31. Cont… Example: Convert 789m to km: 789m x 1km = 0.789km= 7.89x10 -1 km 1000m

32. Cont… 75.00 km x 1000 m x 1 h___ = 20.83m/s h 1 km 3600 s Example: Convert 75.00 km/h to m/s Solution

33. Estimates and Order-of-Magnitude Calculations Estimation problems can be fun to work because you freely drop digits, venture reasonable approximations for unknown numbers, make simplifying assumptions, and turn the question around into something you can answer in your head or with minimal mathematical manipulation on paper

34. Example Estimate the number of breaths taken during an average human life span. Solution

35. Exercise 1) Use information on the endpapers of this book to calculate the average density of the Earth. 2) The standard kilogram is a platinum-iridium cylinder 39.0 mm in height and 39.0 mm in diameter. What is the density of the material? 3) A rectangular building lot is 100 ft by 150 ft. Determine the area of this lot in square meters. 4) An auditorium measures 40.0 m × 20.0 m× 12.0 m. The density of air is 1.20 kg/m 3. What are (a)the volume of the room in cubic feet and (b) (b) the weight of air in the room in pounds? 5) A solid piece of lead has a mass of 23.94 g and a volume of 2.10 cm3. From these data, calculate the density of lead in SI units (kg/m 3 ).