THE SCIENCE OF PHYSICS Holt pgs 3-22

Essential Questions  What is physics?  How is data collected, processed and presented properly and why is this important?  What are some basic math skills I will need to succeed in this course?

Objective  Distinguish physics from other areas of science…so that we know where to look when approaching new ideas and areas of study.  What is Physics? the branch of science concerned with the nature and properties of matter and energy. What are the topics of Physics?

Objective  Associate the SI units used for the measurement of mass, length and time with the instruments used for the measurements of these quantities…so that these measurements can be taken and discussed throughout the year Use the SI (MKS) system of measurement.  SI – International System of Units (Système International d’Unites – French name)  MKS – meter, kilogram, second (most common units)  Established in 1800 in France *Why might it be useful to have a standard system?

SI Units  Units are defined in terms of a standard. 1 meter: the distance light travels in x second. (Measured with a Meterstick) 1 kilogram: is the only unit not defined in terms of properties of atoms. It is the mass of a platinum- iridium metal cylinder kept in Sèvres, France. (measured with a Triple Beam Balance) 1 second: the duration of periods of certain radiation emitted by an atom of cesium-133. (Measured with a Timer)

SI Unit Prefixes:  See your textbook pg. 12 for common prefixes. Ones you should have memorized:  Kilo –  Centi –  Milli –  Mega –  micro How many kisses is 50 kilo kisses? What would you be if you earned 7 megabucks a year?

10 12 Microphones = 1 megaphone 500 millinaries = 1 seminary 2000 mockingbirds = 2 kilomockingbirds 10 cards = 1 decacards fish = 1 microfiche picolos = 10 9 los = 1 gigolo 10 rations = 1 decoration 10 millipedes = 1 centipede 2 snake eyes = 1 paradise 2 wharves = 1 paradox phones = 1 microphone 10 6 phones =1 megaphone mental = 1 centimental mate = 1 decimate bulls = 1 terabull boos = 1 picoboo bismol = 1 femtobismol

Objective:  Use significant digits correctly when recording measured data…so that we can have an idea of how precise our data is and how confident we are in it. RULES: 1. Zeros between other nonzero digits are significant. Ex.: – 6 significant figures 2. If there is a decimal point – only zeros to the right of non-zero digits are significant (not to left) Ex: – 6 significant figures Ex.: – 4 significant figures 3. If there is NO decimal point – zeros to the left are significantZeros in front of nonzero digits are not significant.

3. If there is no decimal point, zeros to the right are not significant. Ex.: – 4 significant figures Extra Practice Here: rial/e/significant_figures_1 rial/e/significant_figures_1

Practice with Sig Figs  How many significant digits are in the following:  A. 3  B. 5  C. 6  D. 8

Practice with Sig Figs  How many significant digits are in the following:  A. 3  B. 4  C. 5  D. 7

Practice with Sig Figs  How many significant digits are in the following:  A. 3  B. 4  C. 5  D. 7

Objective 4  Use significant digits effectively in calculations involving the usual arithmetic operations…so that we are presenting our data and processing correctly.

Operations With Significant Figures  To add or subtract measurements, first perform the operation, then round off the result to the correspond to the least precise value involved.  Ex.: … thousandths 78.9 … tenths … hundredths … thousandths Answer: … tenths

Operations, continued  When multiplying or dividing, first perform the calculation. Then note the factor with the least number of significant figures and round the product or quotient to this number of figures.  Ex.:10.6 … 3 significant digits * … 4 significant digits Answer: 131 … 3 significant digits

 Using significant digits, what is total mass of system which contains a g toy car, 0.3 g piece of string, and paperclips with a total mass of 4.622g?  A g  B g  C g  D. 150 g  E. 200 g

 Using significant digits, what is the area of a room with dimensions of 6.23 m by m?  A m 2  B m 2  C m 2  D m 2

Objective  Distinguish between accuracy and precision … so that we can discuss these two in our lab reports throughout the year.

Accuracy  Accuracy of a measuring device depends upon how well the value obtained agrees with the accepted value.  A measuring device should first be checked for accuracy.  This can be done by using the instrument to measure quantities whose values are known.  The measured values are then compared to the known values.  This is known as calibrating the instrument.

Precision  Precision is the degree of exactness with which the measurement is made or stated.  Precise data is data that is all close to one another  The precision of a measuring instrument is limited by the smallest division on its scale. (see Significant digits in measurement)  Errors in measurements affect the accuracy of a measurement.  But the precision is not affected since values are still stated in terms of the smallest division on the instrument.

Precision vs. Accuracy  Label each of the ducks with the either:  High Accuracy, High precision  High Accuracy, Low precision  Low Accuracy, High precision  Low Accuracy, Low precision

Precision vs. Accuracy

Measurement, Precision and Accuracy

Significant Figures in Measurement  One way of indicating the precision of a measurement is by means of significant figures.  Significant figures should be used throughout the course in laboratory investigations.

The precision of the tool determines the precision of data taken Compare these two measuring tools: What is the reading of the purple line? *** Always estimate to the smallest division plus one more decimal point

Measurement Activity  Using the tool given to you, find the measurement to the correct number of significant digits.  Meterstick – length of the page  Graduated cylinder – volume of water * Then, graph your results with the uncertainty – see next slide for example

Uncertainty in Measurement Suppose the measurement, using the decimeter scale of the meterstick, is 0.23 m. To construct a bar graph of the uncertainty in the measurement extend a bar graph to the 0.2 m mark as in the figure to the right. Darkly shade this region and label it “certain” since we are certain that the length is at least 0.2 m. Certain Decimeter Length in meters

Uncertainty in Measurement, continued Certain Decimeter Length in meters Now extend the bar graph up to the 0.3 m mark. Lightly shade this region and label it “doubtful” since we only know that the length is at least 0.2 m and not more than 0.3 m. Doubtful Now place a line across at 0.23 m.

Questions 1.What determines the precision of a measurement? 2.Explain how a measurement can be precise but not accurate. 3.How does the last digit differ from other digits in a measurement? 4.Your lab partner recorded a measurement as 100 ml. a.What precision has he / she indicated is marked on this cylinder?

Measurement Activity - #2 Record Everything in your Lab/Journal Measure the following items in meters and centimeters using correct sig figs: 1. The width of a floor tile 2. The area of a lab table 3. The volume of the filing cabinet Report your findings on the board

Calculations 1) Calculate the % error for each measurement using: (measured value- accepted value) x 100 Accepted value 2) Looking at your class data, determine the level of precision and accuracy for the class. Be sure to explain your reasoning.

Objective 5  Express numbers correctly in terms of scientific notation and make calculations using a calculator….so that we can do basic calculations on large and small scales throughout the year  Scientific notation the numerical part of a measurement is expressed as a number between 1 and 10 multiplied by a whole-number power of 10. Move the decimal point until only one non-zero digit remains on the left. Then count the number of places the decimal point was moved and use that number as the exponent of ten.  Ex.: 1.04 x 10 3 m; 2.70 x kg

 Which of the following is the number in proper scientific notation?  A * 10 5  B * 10 3  C * 10 6  D * What are the following two numbers multiplied? 1.04 x 10 3 x 2.70 x 10 -4

 Make basic conversions within the metric system and from non-metric to metric… so that we can be confident when dealing with a variety of units. Objective 6

How do we convert between units?  Convert 345 cm to meters (within metric)  Convert 35 micrometers to millimeters  Convert 55miles to kilometers (out of metric) Helpful Conversions: 1.6 km/mile

More conversions  Convert a posted speed limit in the US of 55 miles/hour into (more complex  Meters per second  Kilometers per hour

Objective 8  Describe the process of the scientific method and distinguish between dependent, independent and control variables…so that we can apply it throughout the year  The scientific method is a process used by scientists to examine and/or solve a problem. O BSERVATION – Q UESTION /P ROBLEM –

Scientific model continued… H YPOTHESIS – E XPERIMENT – I NDEPENDENT V ARIABLE : D EPENDENT V ARIABLE : C ONTROL V ARIABLES  D RAW C ONCLUSIONS –  W HAT NEXT ?

 SCIENTIFIC THEORY –  S CIENTIFIC L AW -  S CIENTIFIC M ODEL -

 Consider the observation: “My coffee cools down faster when it is cold out”  Write a problem/question in the proper form:  Independent: ____________________  Dependent: ______________________  Control Variables (give at least 3): Write a hypothesis:

Scientific method – not a linear process…

Scientific Method in Film - wkst T HE S CIENTIFIC M ETHOD IN “M ONTY P YTHON A ND T HE H OLY G RAIL ”  What observation is made at the start of the scene?  What question is posed?  What hypothesis is proposed?  What experiment is performed?  What results are obtained from the experiment?  What conclusion is drawn from the results?  How could they become more sure of this conclusion?

wkst T HE S CIENTIFIC M ETHOD IN “A POLLO 13”  The characters in these scenes also use the scientific method, but not in exactly the steps that we normally identify, as the goal is not to create or support a theory, but to solve a problem.  What observation is made at the beginning of this scene?  What problem is identified?  What needs to be done to solve this problem?  How much detail was required in these procedures? Why?  Is the problem solved in the end? How do they know?