Phys141 Principles of Physical Science

Chapter 1 Measurement

Instructor: Li Ma

Office: NBC 126Phone: (713) 313-7028Email: malx@tsu.edu

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