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.
E = mc2
Physics and the scientific methodAs 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?
0 1 2 3 4 5 6 7 8
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 guessSince each person guesses different, the last digit
shows our error
Error
To Get less error, we use a tool with smaller guesses…
0 1 2 3 4 5 6 7 8
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 significant1, 2, 3, 4, 5, 6, 7, 8, 9
Leading zeros are place holders and not significant
0.0000000000000000002
Trailing zeros are only significant if they are to the right of the decimal
1000000 zeros are not significant
1.00000 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
10000. 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 sideIf the decimal is Absent, we start on the Atlantic sideWe then count from the first NON zero till we run out of digits…
0.05600
Sig Fig Tool Examples
AP 105200
This number has _____ sig figs
4
Sig Fig Tool Examples
AP 105200.
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 1
35.0 cm + 2.98 cm – 7 cm = ?30.98 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 placeWhich gives us the answer of
31 cm
Example 2
3.0 x 89.54 ÷ 0.000000001 = ?268620000000
We have to round to proper sig figs…So we get
300000000000Or in scientific notation
3 x 1011
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 sNow divide
-3.480855296 m/sNow Round
-3 m/s
THE ENDPresentation created by:
Mr. Kern
Information gathered from years of scientific research and data collection
Assignment provided by :BHS Physics Department