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Copyright © 2010 Pearson Education, Inc.
Chapter 1Introduction to physics
Dr. Haykel Abdelhamid Elabidiwebsite: uqu.edu.sa/staff/ar/4331237
Email: [email protected]
mobile: 0564518933
2nd/3rd week of September 2013/DhQ 1434
Copyright © 2010 Pearson Education, Inc.
Course Syllabuls
Copyright © 2010 Pearson Education, Inc.
Course Syllabuls
Copyright © 2010 Pearson Education, Inc.
Units of Chapter 1
• Physics and the Laws of Nature
• Units of Length, Mass, and Time
• Dimensional Analysis
• Significant Figures
• Converting Units
Copyright © 2010 Pearson Education, Inc.
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.
Copyright © 2010 Pearson Education, Inc.
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).
We have to define the units used when measuring the three quantities:
SI (International System of Units) or mks
mks (m: meter, k: kilogramme and s: second)
• 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?
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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 = 10-10mSee Table 1-4 page 5
Copyright © 2010 Pearson Education, Inc.
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 units can be meter or feet or mile…
The dimension of a quantity is denoted 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
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3- Dimensional analysis
Copyright © 2010 Pearson Education, Inc.
3- Dimensional analysis
Exercise 1-2 page 5:
Copyright © 2010 Pearson Education, Inc.
4- Significant Figures
The quotient d/t is calculated using a calculator displaying 8 digits:
d/t=(21.5 cm)/(8.5 s)= 2.4941176 cm/s
The result must be less accurate than the two given numbers :
RULE
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
t is known to 2 significant figures
t is the least known quantity
the speed should be given with 2 significant figures: d/t=2.5 cm/s
21.5 cm 8.5 s
Copyright © 2010 Pearson Education, Inc.
Example 1-1 page 6:A tortoise travels at 2.51 cm/s for 12.23 s. How far does the tortoise go?
only three significant figures
4- Significant Figures
Answer: 2.51 cm/s × 12.23 s = 30.7 cm, and not 30.6973 cm
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,
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.
and not 21.84 s
Copyright © 2010 Pearson Education, Inc.
4- Significant Figures
Copyright © 2010 Pearson Education, Inc.
4- Significant Figures
Copyright © 2010 Pearson Education, Inc.
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
4- Significant Figures
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 ?
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):
5- Converting UnitsConvert 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:
5- Converting UnitsConversion involving any number of units:
Conversion from hours to seconds:
→ The speed will be 9.84 ft/s
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.
5- Converting Units
You can see also Example 1-2 page 9
Active example 1-1 page 9: 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:
Thank you for your attention
See you next time Inchallah
Homework: Ex.5; 6; 7; 8; 9; 11; 12; 13; 14; 15; 17 and 20 page 15
