Phys141 Principles of Physical Science Chapter 1 Measurement Instructor: Li Ma Office: NBC 126 Phone: (713) Webpage: Department of Computer Science & Physics Texas 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 4 th 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): (thousandth) cgs system: centimeter, gram, second Decimal (base-10) system −Simpler when converting from one unit to another

Derived Units Derived QuantityUnit Area (length 2 )m 2, cm 2 Volume (length 3 )m 3, cm 3 Speed (length/time)m/s, cm/s Density (mass/volume)kg/ m 3, g/cm 3

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 = 1x10 3 = 1E3 − = 2.64x10 7 = 2.64E7 − = 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