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