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units 1-5

# units 1-5 - UNIT 1-Measurement Measuring Things Assign a...

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UNIT 1-Measurement Measuring Things Assign a number to an observation of a physical quantity. The measurement is composed of a VALUE and a TYPE. Three basic types of measurement are: LENGTH TIME MASS Other issues: Precision of the measurement. Never add or subtract different types. Can multiply or divide different types to form new physical quantities. The International system of Units With each type of measurement, there is a UNIT for that type. Some SI base units Quantity Unit Name Unit Symbol Length meter m Time second s Mass kilogram kg Other issues: Combinations of base SI units for other types of measurements. Prefixes for SI units. Changing Units To change from one system of base units to another system of base units, one needs to know the CONVERSION FACTORS, (a ratio of units equal to unity.) For example: 1 inch / 2.54 cm = 1 = 2.54 cm / 1 inch See Appendix D Length

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In the book, "The Measure of All Things" by Ken Alder, describes the adventure of determining the standard unit of length, the METER, as one ten-millionth of the distance from the north pole to the equator. The METER was definded as the distance between two marks on platinum-iridium bar. Today, the METER is defined in terms of the distance traveled by a light beam in a specified interval of time. Time In the past, time was defined in terms of the rotating earth "clock". Today, time is defined as "one second = 9,192,631,770 oscillations of the light emmitted by a cesium-133 atomic clock". Here is an interesting experiment. h is your height. Theta is the angle that the earth rotates in the time difference between the "two" sunsets.
Mass SI standard kilogram = the mass of a certain platinium-iridium cylinder kept at the Internation Bereau of Weights and Measures near Paris. Atomic mass standard = the mass of a carbon-12 atom, which has 12 atomic mass units (u). 1 u = 1.6605402 E-27 kg.

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UNIT 2 – Motion Along A Straight Line Motion The study of motion is called kinematics. Some important words: axis (one axis for now) origin (one origin always) direction (one direction for now) particle (one particle for now) Position and Displacement Position or X is the location of a particle on an axis. Displacement is CHANGE in position. Average Velocity and Average Speed Suppose we have a table of values: Time(s) X(m) 1.20 3.54 2.30 5.02 4.10 -1.25 6.80 2.91 8.2 7.40 A graph is a good way to visualize the data.
Average Velocity Vavg = SLOPE of line on the X(t) graph

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Average speed "No direction included" Look at Sample Problem 2-1 to check your understanding. Instantaneous Velocity and Speed The instantaneous velocity is: V(t) is SLOPE of line tangent to the curve on the X(t) graph.
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units 1-5 - UNIT 1-Measurement Measuring Things Assign a...

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