# INTRODUCTION The “stuff” every Physics student should know…

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INTRODUCTION The “stuff” every Physics student should know…

The Metric System Based on powers ten Standards of the metric system: SI units – provides a set of standards of measurement, because it is convenient. Fundamental unit – the base units from which all quantities can be described. Examples: Length – meter(m) Mass – kilogram(kg) Time – second(s)

Derived Unit – combinations of the base units Examples: m/s, m/s/s, Joule Can you think of any others? The Metric System

Prefixes for the Metric System: Femto (F) 10 -15 Pico (p) 10 -12 Tera (T) 10 12 Nano (n) 10 -9 Giga (G) 10 9 Micro (  ) 10 -6 Mega (M) 10 6 Milli (m) 10 -3 Kilo (k) 10 3 Centi (c) 10 -2 Hecto (h) 10 2 Deci (d) 10 -1 Deka (da) 10 1 The Metric System

Conversions – when moving to a larger unit from a smaller unit, move the decimal point to the left the number of spaces (steps) between the prefixes, When moving to a smaller unit from a larger unit, move the decimal point to the right the number of spaces (steps) between the prefixes. DRUL RULE: down to the right, up to the left The Metric System

The Factor- Label Method – converting from one unit to another using a conversion factor. A conversion factor is a fraction that is equal to the number 1. See the worksheet labeled Unit Conversions and Factor Label Method The Metric System

Uncertainty In Measurement All measurements are subject to uncertainties. For example: Parallax – the apparent shift in the position of an object when it is viewed from different angles To avoid this and other discrepancies, we need: Precision – the degree of exactness of a measurement It is limited by the smallest division on the measurement scale

Accuracy – how well the results of an experiment agree with the standard value. Because precision of measuring devices is limited, so is the number of digits in the measurement. See overhead and handout on Accuracy and Precision Uncertainty In Measurement

Significant Figures – “Sig Figs” Sig figs – the valid digits in a measurement All digits 1-9 are significant (123 – three sig figs) Zeros between sig. digits are always significant (5.007 – 4 sig figs) Trailing zeros in a number are only significant if the number contains a decimal point. ( 100.0 – 4 sig figs but 100 – 1 sig fig)

Zeros in the beginning of a number whose only function is to place the decimal point are not significant (0.0025 – 2 sig figs) Zeros following a decimal significant fiure are significant (0.000470 – 3 sig figs, 0.47000 – 5 sig figs) Significant Figures – “Sig Figs”

Rules for calculations using Significant Figures When multiplying and dividing, limit and round to the least number of significant figures in any of the factors. When adding and subtracting, limit and round your answer to the least number of decimal places in any of the numbers that make up your answer. Significant Figures – “Sig Figs”

To avoid confusion with significant figures, we put measurements in scientific notation. This way all significant figures come before the power of ten. Examples: 156,000 1.56 x 10 5 0.0262.6 x 10 -2 0.12601.260 x 10 -4 When performing operations with sig figs, the answer is only as precise as the lesser precise value. See w.s. on calculations with sig figs Significant Figures & Scientific Notation

Graphing Data Independent Variable – the variable that is changed or manipulated, the experimenter can control directly (x –axis) Dependent Variable – the responding variable, this depends on the independent variable (y – axis) Slope = rise =  y run  x

Linear relationship – the dependent variable varies linearly with the independent; the two are directly proportional y = mx + b Direct relationship – as one increases, so does the other Indirect (Inverse) relationship – as one increases, the other decreases Graphing Data

Quadratic relationship – one variable depends on the inverse of the other (the graph is called the parabola) y = mx 2 y = kx 2 Inverse relationship – one variable depends on the inverse of the other y = k(1/X) = k/x or k = xy or y = kx -1 Graphing Data