Presentation on theme: "AP Physics The Right Stuff"— Presentation transcript:
1AP Physics The Right Stuff Units and ProcessLinda Summitt
2Systems of Units, Trigonometry & Vectors Dimensional AnalysisHaving the same units on both sides of an equation does not guarantee that the equation is correct, but having different units on the two sides of an equation certainly guarantees that it is wrong! So it is good practice to reconcile units in problem solving as one check on the consistency of the work. Units obey the same algebraic rules as numbers, so they can serve as one diagnostic tool to check your problem solutions.For example, in the solution for distance in constant acceleration motion, the distance is set equal to an expression involving combinations of distance, time, velocity and acceleration. But the combination of the units in each of the terms must yield just the unit of distance, since the left hand side of the equation has the dimension of distance.Combinations of units pervade all of physics, and doing some analysis of the units is common practice. For example, in the case of centripetal force, it is not immediately evident that the quantity on the right has the dimensions of force, but it must. Checking it out:Physical UnitsMechanics is the branch of physics in which the basic physical units are developed. The logical sequence is from the description of motion to the causes of motion (forces and torques) and then to the action of forces and torques. The basic mechanical units are those ofMass Length TimeAll mechanical quantities can be expressed in terms of these three quantities. The standard units are the Systeme Internationale or SI units. The primary SI units for mechanics are the kilogram (mass), the meter (length) and the second (time). However if the units for these quantities in any consistent set of units are denoted by M, L, and T, then the scheme of mechanical relationships can be sketched out.
4State ObjectiveTo develop basic laboratory skills emphasizing safety as well as problem solving
5Teaching ObjectivesExplain the importance of a standardized system of measureList the SI prefixes and their numerical equivalentsWrite numbers in standard and scientific notationConvert from one metric system to anotherConvert between the metric and English units given conversion factors
6What is That?Each student will be given an odd object in a bag or a box and five minutes to write a description of the object.They will trade the description to another student who will draw the object from their description.The partners will then be allowed to discuss description, objects, and drawings verbally.
7FocusHave you ever tried to describe something to someone who has never seen the thing you are trying to describe? The importance of communication skills and a common knowledge becomes apparent very quickly. Scientist have developed a standard system for communicating data in order to enhance global scientific communication. Learning to use the international system is becoming more important as our society adopts more metric measurements.See the space program mars project.
8How Can Science Help?Science is the systematized, orderly, organized acquisition of information, knowledge and general truths and laws.Much of this organization leads to naming and communication of knowledge.
9ScienceScientific study or science process enables us to pose questions, investigate natural phenomena and solve problems.The skills learned in science help improve daily problem solving abilities.
10Science and Technology Pure science is the acquisition of knowledge for the sake of the knowledge itself. Ex. Collecting information about baseball statisticsApplied science is the practical application of knowledge and is also known as technology ex. Computers
11Limitations in Science Limitations are barriers that prevent science from advancing.Materials, skills, equipment, interpretations, prejudices, etc.
12ScientistsScientists must be curious, observant, organized, and willing to change. Science is full of uncertainties and exceptions. Through communication and collaboration scientists often find that there are different explanations for the same phenomena and different method of solving problems.
13Scientific Method Inductive Method Define the problem Deductive Method Gather informationForm a HypothesisDesign an experimentCarry out the experiment and collect dataAnalyze the dataDraw conclusionsPublishDeductive MethodDefine the problemForm a HypothesisGather informationDesign an experimentCarry out the experiment and collect dataAnalyze the dataDraw conclusionsPublish
14Becoming A Good Problem Solver Understanding and using science process will help you to become a better problem solver in many ways!
15Steps to Good Problem Solving Understand the problem: read and reread, decide what is unknown or asked for, list all the information and laws needed, Break the work up into smaller problems when necessaryAnalyze the data: check for trends and patternsMake a sketch and note any additional information and think about the big picture (diagrams help with signs and principles)Solve the problem (calculus and algebra are applied after substitution)Check the problem does it make sense (Check dimensions)
16PhysicsPhysics studies the fundamental laws of nature and motion of matter.The technology developed through physics overlaps into biological and chemical fields as microcircuits, high-speed computers and imaging are used in medical fields and analytical fields.
17Science MeasurementMeasurement has been important ever since man settled from his nomadic lifestyle and started using building materials; occupying land and trading with his neighbors. As society has become more technologically orientated much higher accuracies of measurement are required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.Body Parts One of the oldest units of length measurement used in the ancient world was the 'cubit' which was the length of the arm from the tip of the finger to the elbow. This could then be subdivided into shorter units like the foot, hand (which at 4 inches is still used today for expressing the height of horses) or finger, or added together to make longer units like the stride. The cubit could vary considerably due to the different sizes of people. As early as the middle of the tenth century it is believed that the Saxon king Edgar kept a "yardstick" at Winchester as the official standard of measurement. A traditional tale tells the story of Henry I ( ) who decreed that the yard should be "the distance from the tip of the King's nose to the end of his outstretched thumb".In November 1900 Queen Victoria handed Bushy House to the Commission of Works for the establishment of a national standards laboratory.NPL was officially opened by the Prince of Wales on 19th March 1902 giving NPL's mission as: "To bring scientific knowledge to bear practically upon our everyday industrial and commercial life, to break down the barrier between theory and practice and to affect a union between science and commerce"
18MeasurementMeasurements, graphs, and models help to bridge the gap between abstract concepts and the concrete. The scales that are chosen in graphing measurements or constructing models allows comparisons to be made and helps to determine the effectiveness of the graph or model
19Using the Body to Measure The “hand”, The “cubit”, The “spanIf the book is 2 hands wide, then it is: 2 hands x (1cubit /5 hands) = .4 cubits wide because 1 cubit = 5 handsThe books and desks are the same but hands vary.
20Standard Units of Measurement What do the following terms mean? DECade CENTury MILLeniumWhy is it important to have standard units of measurement?In order to communicate with others standard units of measurement are necessary
21Measurements Mass : balance Weight: a scale Length: a meter stick Volume: a graduated cylinder or meter stickTemperature: thermometerTime: a stopwatchCurrent: ammeterVoltage: voltmeter
22MeasurementsMass : balance Platinum iridium alloy 100kg/human kg/ horse .1 kg/ frog kg/ text bookWeight: a scaleLength: a meter stick length of light in vacuum 1/ second 91m football field approx length finger tips to mid back 1 mVolume: a graduated cylinder or meter stickTime: a stopwatch the second is 9.19 x 109 the period of 133Cs time between normal heart beat is about 0.8s
24Reviewing Metric and Scientific Notation 103102101.110-210-310-6MetricKiloHectaDekaBase (meter,liter,gram)CentiDeciMilliMicroEnglish trillion billion million thousand hundred10 1210 910 610 310 2
25SI prefixes prefix symbol factor exponential giga G 1,000,000,000 10E9 mega M ,000, E6kilo k , E3hecto h E2deka Dam !0 E-2deci d E1centi c E-2milli m E-3micro u E-6nano n E-9pico p E-12
26Metric Unit Activity Prepare a Mind Map of basic metric units. Begin your tree with four types of measurement: length, volume, mass, temperature.Place the metric bas unit under each name with an object that is approximately one base unit.Place the metric prefixes in order under each base unit.Title: Metric UnitsPrefixes: kilo, hecto, deka, base unit, deci, centi, milliWrite a paragraph explaining why we need the SI measurements.
28Moving the Decimal From To K H D d c m Meter Liter Gram 50 Km 5 0 50,000 m2105 mkm2152.105 km.045 dlml.0445.Dl989 mgKg98kg22 mmm22,000 mm
29UncertaintyWhen a measurement is given, it is also good to state the estimated degree of certainty. If the meter stick measures millimeters, the measurement can be estimated to +/ meters or +/- 0.5 millimeters.The percent uncertainty is the ratio of the uncertainty to the measured value.
30Uncertainty cont’If a value is 53.5 cm the uncertainty is implied +/- 0.1 cm.When using uncertain measurements in calculations (like radius, area, etc.) one can compare the stated value with the “extreme” value.Ex A square has sides 2.5 cm long with uncertainty 0.1cm. Uncertainty of the area equal (2.6 cm cm2).
31Propagation of ErrorEach measurement has an error associated with it determined by the precision of the instrument.These errors introduce small errors into the calculations.Ignoring Significant digits introduces even more error because it creates a false sense of accuracy that does not exist.
34Errors in MeasureErrors in measurements can be calculated by comparing the observed value to the true or expected valueIf you boil water at 95 F and it should boil at 100 F the absolute error = = 5The percent error = 5 / 100 x 100% = 5%Percent error = abs. err. / true value x 100%
35Significant figuresThe last digit in a measurement: usually an estimateWhen adding or subtracting measurements, round the answer to the same decimal place as the measurement with the fewest decimal pointsWhen multiplying or dividing, the result should have the same number of significant figures as the factor with the fewest
36Significant Digits Nonzero digits are always significant. Leading zeros that appear at the start of a number are never significant because they act only to fix the position of the decimal point in a number less than 1.Confined zeros that appear between nonzero numbers are always significant.Trailing zeros at the end of a number are significant only if the number contains a decimal point or contains an over-bar.
37Significant figures 127: 3 320: 2 18000. : 5 0.03000: 4 127: : : : 4It is easiest to convert to scientific notation 1st and then disregard any zeros that are not place holdersSignificant figures are important because when adding, subtracting, multiplying, or dividing measurements the final answer can not be more accurate than the least accurate measurement
38Scientific NotationThe measurement is expressed as the product of 2 numbers, the numerical value expressed as a number between 0 & 10 and a power of 10
39Scientific Notation 520 = 5.2 x 102 0.0037 = 3.7 x 10-3 0.223 = 5301 = ===
40Scientific Notation 520 = 5.2 x 102 0.0037 = 3.7 x 10-3 0.223 = 5301 = ===
41Scientific NotationWhen multiplying or dividing in scientific notation add or subtract the exponents respectively.Writing numbers as a product of a number between 1 thru 9 and powers of ten
42Adding and Subtracting When adding or subtracting numbers in scientific notation the numbers must have the same power.4.1 x 10-6 kg x 10-7 kg =4.02 x 106 m x 102 m =
44Scientific NotationExponents must agree to add or subtract in scientific notation.
45Multiplying & Dividing When multiplying or dividing in scientific notation, the number itself can simply be multiplied or divided. If the operation is multiplication the powers should be added. If the operation is division, the powers should be subtracted.(4 x 103 kg) (5 x 1011 m) =8 x 106m3 / 2 x 10-3m2 =
47Converting Metric to Metric Write the measurement and units as a quotientFind a conversion factor with the same unitsMultiply the measurement by the conversion factor being sure that the like measurement cancels
48Converting metric to metric 2300ml = _____ L27056 ml = _____ dekaliters0.0683m = ______ mm
49Converting metric to metric 2300ml = _____ L27056 ml = _____ dekaliters0.0683m = ______ mm
50Conversion Factors 2.54 cm = 1 in 1 m = 39.37 in 28.35 g = 1 oz g = 1 lb1 kg = 2.2 lb0.946 L = 1 qt L = 1.06 qt1000cm3 = 1L H2O at 40C1 mL = 1 cc = 1 cm3 = 1 g H2O at 40CK = 0C C = 5/9 (0F – 320)0F = 9/5 0C + 32
51Converting Metric to English Converting between English and metric is very similar to converting metric to metricWrite the measurement as a quotientMultiply the measurement by the proper conversion factor(s) being sure the units cancelCancel units, and complete math
52Converting between English and metric 1 in = 2.54cm 1 lb = kg20 kg = ________lb20kg x lb = kg kg.0563m = ________ in
53Converting between English and metric 1 in = 2.54cm 1 lb = kg20 kg = ________lb.0563m = ________ in
54Accuracy, Precision & Parallax Accuracy shows the difference between the “true value” and he average of the measurements.Precision shows how much a measurement differs from the average measurement.Parallax- displacement of a reading due to different viewing angleWatch out for these when making measurementsaccurate
55Accuracy in measurement The rule below is marked off at every 1/8th of an inch (.125 inch). When measuring with this ruler one could estimate +or- to the 16th of an inch with this ruler.How long would You estimate the bar to be?
56Are the numbers 8.79, 8.77, 8.78, 8.78, 8.79, & 8.8 accurate or precise if they are experimental values for the acceleration of gravity which is 9.81 m/s2?AccuratePreciseNeitherBoth
57Order of Magnitude Estimations Calculations that are made using estimated data can be very useful.The calculations are also guesses and are called order of magnitude estimates.Many times you can make an estimate of tens, hundreds, thousands etc. this is the order of magnitude.
58Order of MagnitudeEstimate the gallons of gas used in the US per year.300 mill people family of car per family 3 x 108 people / 4people/car x 10,000 mi/year = 7.5 x 1011 mi/year/carIf each car gets 20 mi per gal x 1011 mi/year/ 20 mi/gal = 3.8 x 1010 gal/year
59Matter and Measurement Matter is anything that has mass and volume.Mass is a specific quantity of a substance.Volume is the space the substance occupies (l x w x h).Atoms are the particles that make up matter; the characteristics or properties of the atoms in a substance determine the properties of the substance and many of theses properties can be measured using both simple and complicated techniques
60Matter & AtomsEarly studies in Alchemy led to discovery of the “non-sliceable” atom by Greeks Leucippus and Democritus.By the 1900’s the nucleus had been discovered following the model of the solar system.By the 1930’s atomic number had been defined as the number of protons and was used to identify elements and the atomic mass as the average number of protons and neutrons.
61Electrons & QuarksIt was determined that there were smaller particles known as electrons that were negative charge carriers spinning around the nucleus.It was discovered that smaller particles known as quarks (up, charmed, and top :+2/3 and down, strange and bottom :-1/3) combine to make the protons (+2/3 +2/3 -1/3) and neutrons (-1/3 1/3 +2/3)
62Derived UnitsDerived units are measurements that are a combination of two or more basic units.Derived units are defined by a mathematical equation. Ex: Density = mass/ volume
63What is Density?Density is how much mass there is in a specific volume.Density is the number of particles / amount of space.Differences in density are related to differences in atomic mass
64Density-A Property of Matter Density = the mass/ the volume.Density can be determined by graphing the mass of several different volumes of a substance and finding the slope of the line.
65Graphing DensityIf the mass of several volumes was collected and plotted to give the following graph, the density could be determined as shown.60g 50g 40g 30g 20g 10g 0g215mL 10mL 15mLSlope = y2-y1 / x2-x1= 30 – 10 / 10 – 5= 20/5 = 4 g/mL
66Graphs and TablesGraphs and tables are used to organize information so that trends, changes and parts of a whole can be easily detected and predictions can be made.Both should be labeled clearly.Their are many different kinds of graphs and tables.Bar graphs, pie charts, line graphs, curve graphs, spread sheets, comparison tables ETC.
67GraphsGraphs are representations of complex phenomena. They are a type of model and can be used to visualize relationships between variables.
68Graphs All graphs should have the following Title Choose units for the axisChoose the scale 10s 100s etcLabel the axisPlot dataAnalyze data
70Analysis-Using your DATA Look for patterns, relationships, cause & effect, and supporting or contradicting data.Prepare charts, graphs, or database.
71Using Equations! Read Carefully!!! Draw Pictures! Write expressions for knowns and unknownsLabel drawingsWrite an equationSolveCheck to be sure it makes sense and answers the question
72Molar Mass & Avagadro’s # 12C has exactly 6 protons and 6 neutrons. 12 g of 12C has x1023 atoms in it.This is defined as a mole!1 mole of any substance has x particles and has a mass equal to the atomic mass of the substance .matom =molar mass/NavagadroHow much mass would 2 moles of iron have?
73Dimensional AnalysisMeasurements have magnitude and dimensions or a number and units. These cannot be separated!!!Quantities can be added and subtracted only if they are the same units or dimensions!Terms on either side of an equation must have the same units on either side of the equation to be valid.Ex. l=m v=l/t =m/s a=l/t2=m/s2Show
76ConclusionsThe analysis is made more understandable or summarized.Theories are formed from supporting evidence.New focus or extension should be suggested.
77SummaryThe Scientific Method of Problem Solving Can help solve all types of problems and enhance decision making abilities. If the knowledge gained through science is shared systematically all of society can benefit from the knowledge and technology.
80Trigonometric Functions Sin q = opp / hypCos q= adj / hypTan q= opp / adjhypoppqadj
81Scalar and VectorScalar: quantities with magnitude but no direction 60 miles / hrVector: quantities with magnitude and direction 60 miles / 600 N
82Trigonometric Functions Sin q = opp / hypCos q= adj / hypTan q= opp / adjPythagoreansC2 = A2 + B2ChypBoppqadjA
83Scalar and VectorScalar: quantities with magnitude but no direction 60 miles / hrVector: quantities with magnitude and direction 60 miles / 600 N
84Position VectorsAny point has a set of coordinates that defines its position. A line can be drawn from the origin to the coordinates. This line is a position vector and is written in bold or as a lower case r with an arrow above it.P (2,3)(x,y)3r2
85DisplacementDisplacement is a change in position over time. It is a vector quantity.Vectors that have the same direction are parallel.Vectors that have the same magnitude and direction are equal even if they start from different points.
86Planar-polar Coordinates Point P is distance r from the origin and angle q from the reference line+ is ccw-is cwrq
87Vectors, resultants and equilibrants Vectors are added graphically by placing the tail of one vector at the head of the other vector.The sum of the vectors is known as the RESULTANT. The resultant is drawn from the tail of the first vector to the head of the last vector.The EQUILIBRANT is a force that can be applied to a non-zero net force to balance that force.When the net forces acting on a point are zero the forces are at equilibrium.
88Vector Addition in Two Dimensions Vectors are added by placing the tail of one vector at the head of the other vector.Graph paper and a protractor may be used to resolve vectors.
89Addition of several vectors Three or more vectors can be added in the same way. The direction and length of the vector must be to scale and must not be changed.
90Vector Quantities are Independent Perpendicular vector quantities are independent.Ex. the velocity north or south does not change the velocity east or westIf a boat is traveling at 9.4 m/s at 32 N and it crosses a river 80 meters wide and the boat’s velocity is 8 m/s east, then it takes 10 seconds for the boat to cross the river. The boat will drift north 50 meters during that time.
91Pythagorean’s Theorem and resultant vectors The resultant vector of two perpendicular vectors is the hypotenuse of a right triangle, therefore, Pythagorean theorem can be used to determine the resultantIf a 110 N North force and a 55 N East force act on an object and the forces are applied at right angles, then the resultant force is equal to the square root of 1102 and 552 or 123 N.
92Trigonometric functions and resultant angles The angle of the resultant vector can be found by using one of the trigonometric functions such as:= Opposite side / Hypotenuse= Adjacent side / Hypotenuse= Opposite side / Adjacent sideThe resultant angle in the above problem is found : 110/55 = = = 64 degrees
93Resolve a vector into its horizontal and vertical components A single vector can be broken down into its COMPONENTS . Any vector can be thought of as the resultant of two components.Ex. The boat traveling at 9.4 m/s at 32 N can be RESOLVED into two components: 10 m/s east and 5 m/s NVECTOR RESOLUTION is the process of finding the magnitude of the components in each direction.
94Adding Vectors at Angles through vector resolution. When adding vectors at angles: 1st resolve each vector into its components, 2nd add all of the vertical components, 3rd add all of the horizontal componentsThe resultant vector is the resultant of the sum of the vertical vectors and the sum of the horizontal vectors.Ex. A force of 12N at 10 N and a force of 14N at can be broken down to E and 2.1N and 9.0 E and 10.7 S. The horizontal sum is 20.8 E and the vertical sum is 8.6 S . The resultant using Pythagorean Theorem is 22.5 N and using the laws of trigonometry the angle is 22.5 SE
95Subtraction of Vectors To subtract vector B from vector A, reverse the direction of vector B and add it to vector A
96Vector ProductsTwo vectors originating at the same point can be multiplied together to get the vector product.A x B = AB cos t where A & B are the magnitude of A and BEx A is N of E and B is 5.0 at 770 N of E then the vector product is 4.0 x 5.0 x cos 770
97Problem SolvingThe key to successful problem solving is to ask the right question !Go back to the simplest thing that you know.Work forward from that simple knowledge
98SummaryCharts and tables will always be available to help you convert measurements in the metric system. Students should know how to use the charts and tables to become familiar with the metric system