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Chapter 1 Introduction to physics

Chapter 1 Introduction to physics. Dr. Haykel Abdelhamid Elabidi. 2 nd /3 rd week of September 2013/DhQ 1434. Course Syllabuls. Course Syllabuls. Units of Chapter 1. Physics and the Laws of Nature Units of Length, Mass, and Time Dimensional Analysis Significant Figures

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Chapter 1 Introduction to physics

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  1. Chapter 1Introduction to physics Dr. Haykel Abdelhamid Elabidi 2nd/3rd week of September 2013/DhQ 1434

  2. Course Syllabuls

  3. Course Syllabuls

  4. Units of Chapter 1 • Physics and the Laws of Nature • Units of Length, Mass, and Time • Dimensional Analysis • Significant Figures • Converting Units

  5. 1- What is Physics • Physics is the study of the fundamental laws of nature. These laws can be expressed as mathematical equations. • It is the science of measurements and experimental. • Physicist (scientist who studies Physics) observes the phenomena of nature and try to find patterns and principles that relate these phenomena.

  6. 2- Units of Length, Mass and Time • To make quantitative comparison between the laws of physics and our experiments, certain basic physical quantities must be measured. • We use here three basic quantities: length (L), mass (M) and time (T). • Mohamed measures the length of the room wall with a ruler, he gives us a value of 5. • Abdullah measures the same length, he gives us a value of about 16. What is the real value of the length? We have to define the unitsusedwhenmeasuring the threequantities: SI (International System of Units) or mks mks (m: meter, k: kilogramme and s: second)

  7. 2- Units of Length, Mass and Time • Unit of Length: meter (m) One meter is the distance traveled by light in a vacuum in 1/299,792,458 of a second. See Table 1-1 page 3 • Unit of Mass: kilogramme (kg) One kilogram is the mass of a particular platinum-iridium (Pt– Ir) cylinder kept at the International Bureau of Weights and Standards, France. See Table 1-2 page 3 • Unit of Time: second (s) One second is the time required for a cesium(Cs)-133 atom to undergo 9,192,631,770 vibrations. See Table 1-3 page 4 The standard prefixes are used to designate common multiples in powers of ten. Exemples: 1mm =10-3m, 1km=10+3 m, 1cm = 10-2 m, 1micro= 10-6 m,1angstrom = 10-10m See Table 1-4 page 5

  8. 3- Dimensional analysis • The dimension in physics refers to the type of quantity regardless of the unit used. • Ex. a distance has a dimension of length, but the unitscanbemeter or feet or mile… • The dimension of a quantityisdenoted in brackets: • Length [L], Mass [M], Time [T] • Any valid physical formula must be dimensionally consistent (each term must have the same dimensions) • This type of calculation with dimensions is called dimensional analysis

  9. 3- Dimensional analysis

  10. 3- Dimensional analysis Exercise 1-2 page 5:

  11. 4- Significant Figures The quotient d/t is calculated using a calculator displaying 8 digits: d/t=(21.5 cm)/(8.5 s)= 2.4941176cm/s We can’t expect to measure quantities with two and three significant figures and from them obtain results with eight significant figures: RULE 8.5 s 21.5 cm The number of significant figures after multiplication or division is equal to the number of significant figures in the least accurately known quantity. In our example: d is known to 3 significant figures the speed should be given with 2 significant figures: t is known to 2 significant figures d/t=2.5 cm/s t is the least known quantity

  12. 4- Significant Figures Example 1-1 page 6: A tortoise travels at 2.51 cm/s for 12.23 s. How far does the tortoise go? Answer: 2.51 cm/s × 12.23 s = 30.7 cm, and not 30.6973 cm only three significant figures You measure a time of 16.74 s, then you measure another time of 5.1 s The total measured time is 21.8 s, and not 21.84 s RULE The number of decimal places after addition or subtraction is equal to the smallest number of decimal places in any of the individual terms.

  13. 4- Significant Figures

  14. 4- Significant Figures

  15. 4- Significant Figures 2500 0.000036 Each of these numbers has two significant figures 2500 = 2.5 × 103 If we write 2.50x103, it has three significant figures 0.000036 = 3.6 x 10-5 Exercise 1-4 page 7 How many significant figures are there in (a) 21.00, (b) 21, (c) 2.1x10-2, (d) 2.10x10-3 ?

  16. 5- Converting Units We want to convert a distance of 225 ft to meters (m): We use the conversion factor 1m=3.281 ft and To make the conversion from feet (ft) to meters (m), we multiply 225 ft by the first factor (1 m/3.281 ft): To make the conversion of 24.3 meters (m) to feet (ft), we multiply it by the second factor (3.281 ft/1 m):

  17. 5- Converting Units Convert the distance d=3.00 mi to meters. 1 mi=5280 ft First conversion: mi ft: Second conversion: ft m: We can do this in a single calculation:

  18. 5- Converting Units Conversion involving any number of units: You walk at 3.00 m/h, how fast is that in ft/s ? 1h=3600 s We need the conversion of 3.00 mi to meters (this was done before) and then the conversion of 1h to seconds. → The speed will be 9.84 ft/s Conversion from hours to seconds:

  19. 5- Converting Units

  20. 5- Converting Units Example 1-1 page6: Blood in the human aorta can attain speeds of 35.0 cm/s. How fast is this in (a) ft/s and (b) mi/h? Solution: You can see also Example 1-2 page 9

  21. Homework: Ex.5; 6; 7; 8; 9; 11; 12; 13; 14; 15; 17 and 20 page 15 Thankyou for your attention Seeyounext time Inchallah

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