phys141 principles of physical science chapter 1 measurement
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Phys141 Principles of Physical Science Chapter 1 Measurement. Instructor: Li Ma Office: NBC 126 Phone: (713) 313-7028 Email: [email protected] Webpage: http://itscience.tsu.edu/ma Department of Computer Science & Physics Texas Southern University, Houston. Sept. 8, 2004. Measurement. - PowerPoint PPT PresentationTRANSCRIPT
Phys141 Principles of Physical Science
Chapter 1 Measurement
Instructor: Li Ma
Office: NBC 126Phone: (713) 313-7028Email: [email protected]
Webpage: http://itscience.tsu.edu/ma
Department of Computer Science & PhysicsTexas Southern University, Houston
Sept. 8, 2004
Measurement
• Measurements in our daily life: length/height weight/mass time temperature pressure Others
• First step to understand our physical environment
• Describe the nature
• Use our senses to make measurements
The Senses
• 5 senses make it possible to know the environment: sight, hearing, touch, taste, smell: provide information
• Limitations of sense: for example, telescope to distinguish the stars,
microscope for the cell may also provide false information can be reduced or eliminated by using measuring
instruments
• Instruments have their limitations: accuracy limits
• Scientific method will tell us how to deal with them
Systems of Units
• Units− Express measurements− Describe things in a concrete way – that is, numerically
• Standard unit− fixed and reproducible value for the purpose of taking
accurate measurements
• Systems of units− Metric system− British system
Systems of Units (cont)
• Fundamental physical quantities
− length, mass, time, etc.
• Length
− Description of space: location/size
− Measurement of space in any direction: length
− “meter” in metric system
− “foot” in British system
Systems of Units (cont)
• Mass
− The amount of matter an object contains
− Can be defined in terms of force and acceleration, and gravity
− “kilogram” in metric system
− Mass is fundamental quantity, not weight:
Mass doesn’t change when measured in different place
Systems of Units (cont)
• Time
− Duration, period, interval
− The continuous, forward flowing of events
− Only one direction – forward
− The 4th dimension of the space
− “second” in both metric system and British system
More on Metric System
• mks system
• International Standard System (SI): 7 base units− Meter (m)− Kilogram (kg)− Second (s)− Ampere (A): measure the flow of electric charge− Kelvin (K): measure the temperature− Mole (mol): measure the amount of a substance− Candela (cd): measure luminous intensity
More on Metric System (cont)
• Metric prefixes− mega- (M): 1,000,000 (million)− kilo- (k): 1,000 (thousand)− centi- (c): 0.01 (hundredth)− milli- (m): 0.001 (thousandth)
• cgs system: centimeter, gram, second
• Decimal (base-10) system− Simpler when converting from one unit to another
Derived Units
Derived Quantity Unit
Area (length2) m2, cm2
Volume (length3) m3, cm3
Speed (length/time) m/s, cm/s
Density (mass/volume) kg/ m3, g/cm3
Conversion Factors
• Conversion Factor− Relate one unit to another: 1 in. = 2.54 cm− Ration from an equivalence statement
• Steps for converting:• Step 1: choose a conversion factor• Step 2: cancel the unwanted unit• Step 3: check the remained unit
Significant Figures
• Rules for number of significant figures to keep in operations
− In multiplying and dividing, the least number of significant figures
− In adding and subtracting, the least number of decimal places
• Rules for rounding− If the first digit to be dropped is less than 5, leave the
preceding digit as it− If the first digit to be dropped is 5 or greater, increase the
preceding digit by 1
Scientific Notation
• Power of 10− 1000 = 1x103 = 1E3− 26400000 = 2.64x107 = 2.64E7− 0.00000264 = 2.64x10-6 = 2.64E-6
• Rules for using this notation− The exponent, or power of 10, is increased by 1 for every
place the decimal point is shifted to the left− The exponent, or power of 10, is decreased by 1 for every
place the decimal point is shifted to the right