INTRO TO PHYSICS AND MEASUREMENT

What is Physics?  Physics   The study of matter  and energy and how they interact  This year we will study a broad spectrum of many different areas of physics

Branches of Physics  Mechanics   the study of motion and its causes.  Mechanics can also be separated into smaller sub categories.  We will spend the majority of the fall semester discussing these sub categories of mechanics Kinematics – the study of objects in motion Dynamics – the study of forces and the causes of motion Energetics – the study of energy transformations

Branches of Physics  Thermodynamics   The study of heat and temperature.  In this area we will also discuss the nature of phase changes and the fluid state

Branches of Physics  Harmonic motion   This area of physics involves the study of repetitious motion and waves

Branches of Physics  Electromagnetism   This area of study involves the study of how electricity and magnets work and effect the world around us.

Branches of Physics  Optics   This area of study involves the study of light and how it is used by us as people.

Branches of Physics  Relativity   This is the branch of physics that discusses Einstein’s theories of the cosmos.

Physics and the scientific method  As with all sciences, what makes our study of physics possible is the scientific method. You have learned about the scientific method in many of your previous science classes, so we will not spend as much time discussing it here.

So what are the steps (parts) of the scientific method? Question or problem – this is what inspires us to DO science. Without a question, our investigation stops. Observation – In doing science, we observe the world around us using our five sense and other methods of measurement Hypothesis – This is the point in which we make a “guess” based on our observations and previous knowledge about what should happen, or why something happens Experimentation – the testing of the hypothesis is what makes science an effective process for solving problems and answering questions The experiment is where we take our measurements and collect our data. Evaluation – this is the point in the process, commonly referred to as the conclusion, where we decide if our hypothesis is correct or not based on our experimental results.

Measurement in the scientific method  The key to a good experiment is being able to make good measurements and record our data in the proper way.  If we do not make good measurements, we will have incorrect data. Incorrect data results in bad results and wrong conclusions.

What Makes a Good Measurement?  Accuracy –  how close your measurement is to the correct value  Precision –  how close one measurement is to all other measurements in the experiment

Error  ALL MEASUREMENTS HAVE ERROR  So what is error?  Error is a measure of how far off you are from correct  Error depends on a number of different factors, but the main source of error is the tools we use to make the measurements  The accuracy of a measurement is dependent upon the tools we use to make the measurement.

Error  When recording our measurement, we have to make a guess…the guess shows our error…the smaller the guess, the more accurate our measurement…  How long is the box? I know the measurement is at least 5 cm… cm But since there are not marks between the centimeters, that is all we know for sure… So we guess…5.8cm, the last digit shows our guess Since each person guesses different, the last digit shows our error

Error  To Get less error, we use a tool with smaller guesses… What is the measurement with a more accurate tool? 5.91 cm…the 1 is a guess

Minimizing Error  There are many ways to minimize your error in measurement, but the main ways are…  Using more accurate tools – since your measurement can only be as accurate as your tool, if your tool is more accurate, your measurement will be more accurate.  Avoiding parallax – parallax is the apparent shift in location due to the position of an observer…

Using Measurements  Since our measurements all have error, when we use them in calculations, we have to carry the error through…  How do we do this you ask?  Significant Figures…

Significant Figures  Significant figures are scientists way of showing accuracy in measurements and in calculations  JUST BECAUSE IT IS ON YOUR CALCULATOR SCREEN DOES NOT MAKE IT SIGNIFICANT!

Rules for Identifying sig. figs. In a Measurement  All non-zero digits are significant 1, 2, 3, 4, 5, 6, 7, 8, 9  Leading zeros are place holders and not significant  Trailing zeros are only significant if they are to the right of the decimal  zeros are not significant  zeros are significant  Zeros between two significant figures, or between a significant digit and the decimal are significant 101  zero is signigicant 10.0  all zeros are significant  all zeros are significant

Significant Figures  So, is there an easy way to figure this out without memorizing the rules…  YES!

Sig Fig Tool AP We will use our great nation to identify the sig figs in a number… On the left of the US is the Pacific and on the right is the Atlantic

Sig Fig Tool AP If we write our number in the middle of the country we can find the number of sig figs by starting on the correct side of the country… If the decimal is Present, we start on the Pacific side If the decimal is Absent, we start on the Atlantic side We then count from the first NON zero till we run out of digits…

Sig Fig Tool Examples A P This number has _____ sig figs 4

Sig Fig Tool Examples A P This number has _____ sig figs 6

Calculations with significant figures  Since our measurements have error, when we use them in calculations, they will cause our answers to have error.  Our answer cannot be more accurate than our least accurate measurement.  This means that we have to round our answers to the proper accuracy…

Calculations with significant figures  When we add or subtract, our error only makes a small difference. So, when adding or subtracting we base our rounding on the number of decimal places.  Rule for Adding and Subtracting – the answer must have the same number of decimal places as the measurement used in the calculation that has the fewest decimal places

Calculations with significant figures  When we multiply or divide, our error makes a large difference. So, when multiplying or dividing numbers, we round based on significant figures.  Rule for Multiplying and Dividing – the answer must have the same number of significant figures as the measurement used in the calculation that has the fewest significant figures

Example cm cm – 7 cm = ? cm This is what your calculator gives you… However, as we just discussed, the answer cannot be more accurate than your least accurate measurement… The least accurate measurement is 7 cm… So by the adding rule, our answer must be rounded to zero decimal places, or the ones place Which gives us the answer of 31 cm

Example x ÷ = ? We have to round to proper sig figs… So we get Or in scientific notation 3 x 10 11

Example 3  What if we have both add/sub and mult/div in the same problem? (2.4 m + 5 m) ÷ (1.889s – 3.9 s) = ? Order of opperations means we do the addition and subtraction first… (7.4 m) ÷ (-2.011s) We have to round these before we go on to the division… 7 m ÷ -2.0 s Now divide m/s Now Round -3 m/s

THE END Presentation created by: Mr. Kern Information gathered from years of scientific research and data collection Assignment provided by : BHS Physics Department