# AP Physics The Right Stuff

## Presentation on theme: "AP Physics The Right Stuff"— Presentation transcript:

AP Physics The Right Stuff
Units and Process Linda Summitt

Systems of Units, Trigonometry & Vectors
Dimensional Analysis Having 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 Units Mechanics 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 of Mass Length Time All 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.

Science Process & Metrics
Linda Summitt

State Objective To develop basic laboratory skills emphasizing safety as well as problem solving

Teaching Objectives Explain the importance of a standardized system of measure List the SI prefixes and their numerical equivalents Write numbers in standard and scientific notation Convert from one metric system to another Convert between the metric and English units given conversion factors

What 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.

Focus Have 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.

How 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.

Science Scientific 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.

Science and Technology
Pure science is the acquisition of knowledge for the sake of the knowledge itself. Ex. Collecting information about baseball statistics Applied science is the practical application of knowledge and is also known as technology ex. Computers

Limitations in Science
Limitations are barriers that prevent science from advancing. Materials, skills, equipment, interpretations, prejudices, etc.

Scientists Scientists 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.

Scientific Method Inductive Method Define the problem Deductive Method
Gather information Form a Hypothesis Design an experiment Carry out the experiment and collect data Analyze the data Draw conclusions Publish Deductive Method Define the problem Form a Hypothesis Gather information Design an experiment Carry out the experiment and collect data Analyze the data Draw conclusions Publish

Becoming A Good Problem Solver
Understanding and using science process will help you to become a better problem solver in many ways!

Steps 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 necessary Analyze the data: check for trends and patterns Make 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)

Physics Physics 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.

Science Measurement Measurement 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"

Measurement Measurements, 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

Using the Body to Measure
The “hand”, The “cubit”, The “span If the book is 2 hands wide, then it is: 2 hands x (1cubit /5 hands) = .4 cubits wide because 1 cubit = 5 hands The books and desks are the same but hands vary.

Standard Units of Measurement
What do the following terms mean? DECade CENTury MILLenium Why is it important to have standard units of measurement? In order to communicate with others standard units of measurement are necessary

Measurements Mass : balance Weight: a scale Length: a meter stick
Volume: a graduated cylinder or meter stick Temperature: thermometer Time: a stopwatch Current: ammeter Voltage: voltmeter

Measurements Mass : balance Platinum iridium alloy 100kg/human kg/ horse .1 kg/ frog kg/ text book Weight: a scale Length: a meter stick length of light in vacuum 1/ second 91m football field approx length finger tips to mid back 1 m Volume: a graduated cylinder or meter stick Time: a stopwatch the second is 9.19 x 109 the period of 133Cs time between normal heart beat is about 0.8s

Reviewing Metric and Scientific Notation
103 102 10 1 .1 10-2 10-3 10-6 Metric Kilo Hecta Deka Base (meter,liter,gram) Centi Deci Milli Micro English trillion billion million thousand hundred 10 12 10 9 10 6 10 3 10 2

SI prefixes prefix symbol factor exponential giga G 1,000,000,000 10E9
mega M ,000, E6 kilo k , E3 hecto h E2 deka Dam !0 E-2 deci d E1 centi c E-2 milli m E-3 micro u E-6 nano n E-9 pico p E-12

Metric 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 Units Prefixes: kilo, hecto, deka, base unit, deci, centi, milli Write a paragraph explaining why we need the SI measurements.

Metric Measurements Activity

Moving the Decimal From To K H D d c m Meter Liter Gram 50 Km 5 0
50,000 m 2105 m km 2 1 5 2.105 km .045 dl ml .0 4 45.Dl 989 mg Kg 9 8 kg 22 m mm 22,000 mm

Uncertainty When 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.

Uncertainty 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).

Propagation of Error Each 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.

Propagation of Error Addition & Subtraction

Propagation of Error Multiplication and Division

Errors in Measure Errors in measurements can be calculated by comparing the observed value to the true or expected value If you boil water at 95 F and it should boil at 100 F the absolute error = = 5 The percent error = 5 / 100 x 100% = 5% Percent error = abs. err. / true value x 100%

Significant figures The last digit in a measurement: usually an estimate When adding or subtracting measurements, round the answer to the same decimal place as the measurement with the fewest decimal points When multiplying or dividing, the result should have the same number of significant figures as the factor with the fewest

Significant 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.

Significant figures 127: 3 320: 2 18000. : 5 0.03000: 4
127: : : : 4 It is easiest to convert to scientific notation 1st and then disregard any zeros that are not place holders Significant figures are important because when adding, subtracting, multiplying, or dividing measurements the final answer can not be more accurate than the least accurate measurement

Scientific Notation The measurement is expressed as the product of 2 numbers, the numerical value expressed as a number between 0 & 10 and a power of 10

Scientific Notation 520 = 5.2 x 102 0.0037 = 3.7 x 10-3 0.223 = 5301 =
= = =

Scientific Notation 520 = 5.2 x 102 0.0037 = 3.7 x 10-3 0.223 = 5301 =
= = =

Scientific Notation When 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

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 =

Scientific Notation Exponents must agree to add or subtract in scientific notation.

Multiplying & 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 =

Converting Metric to Metric
Write the measurement and units as a quotient Find a conversion factor with the same units Multiply the measurement by the conversion factor being sure that the like measurement cancels

Converting metric to metric
2300ml = _____ L 27056 ml = _____ dekaliters 0.0683m = ______ mm

Converting metric to metric
2300ml = _____ L 27056 ml = _____ dekaliters 0.0683m = ______ mm

Conversion Factors 2.54 cm = 1 in 1 m = 39.37 in
28.35 g = 1 oz g = 1 lb 1 kg = 2.2 lb 0.946 L = 1 qt L = 1.06 qt 1000cm3 = 1L H2O at 40C 1 mL = 1 cc = 1 cm3 = 1 g H2O at 40C K = 0C C = 5/9 (0F – 320) 0F = 9/5 0C + 32

Converting Metric to English
Converting between English and metric is very similar to converting metric to metric Write the measurement as a quotient Multiply the measurement by the proper conversion factor(s) being sure the units cancel Cancel units, and complete math

Converting between English and metric
1 in = 2.54cm 1 lb = kg 20 kg = ________lb 20kg x lb = kg kg .0563m = ________ in

Converting between English and metric
1 in = 2.54cm 1 lb = kg 20 kg = ________lb .0563m = ________ in

Accuracy, 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 angle Watch out for these when making measurements accurate

Accuracy 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?

Are 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? Accurate Precise Neither Both

Order 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.

Order of Magnitude Estimate 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/car If each car gets 20 mi per gal x 1011 mi/year/ 20 mi/gal = 3.8 x 1010 gal/year

Matter 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

Matter & Atoms Early 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.

Electrons & Quarks It 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)

Derived Units Derived 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

What 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

Density-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.

Graphing Density If 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 0g 2 1 5mL 10mL 15mL Slope = y2-y1 / x2-x1 = 30 – 10 / 10 – 5 = 20/5 = 4 g/mL

Graphs and Tables Graphs 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.

Graphs Graphs are representations of complex phenomena. They are a type of model and can be used to visualize relationships between variables.

Graphs All graphs should have the following Title
Choose units for the axis Choose the scale 10s 100s etc Label the axis Plot data Analyze data

Look for patterns, relationships, cause & effect, and supporting or contradicting data. Prepare charts, graphs, or database.

Using Equations! Read Carefully!!! Draw Pictures!
Write expressions for knowns and unknowns Label drawings Write an equation Solve Check to be sure it makes sense and answers the question

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/Navagadro How much mass would 2 moles of iron have?

Dimensional Analysis Measurements 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/s2 Show

Common Geometry Formulas
w h l w r h l h r b b h h r a

Mathematical Notations

Conclusions The analysis is made more understandable or summarized. Theories are formed from supporting evidence. New focus or extension should be suggested.

Summary The 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.

Vector Analysis

Pythagorean’s Theorem
C2=A2+B2 A C B

Trigonometric Functions
Sin q = opp / hyp Cos q= adj / hyp Tan q= opp / adj hyp opp q adj

Scalar and Vector Scalar: quantities with magnitude but no direction 60 miles / hr Vector: quantities with magnitude and direction 60 miles / 600 N

Trigonometric Functions
Sin q = opp / hyp Cos q= adj / hyp Tan q= opp / adj Pythagoreans C2 = A2 + B2 C hyp B opp q adj A

Scalar and Vector Scalar: quantities with magnitude but no direction 60 miles / hr Vector: quantities with magnitude and direction 60 miles / 600 N

Position Vectors Any 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) 3 r 2

Displacement Displacement 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.

Planar-polar Coordinates
Point P is distance r from the origin and angle q from the reference line + is ccw -is cw r q

Vectors, 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.

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.

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.

Vector Quantities are Independent
Perpendicular vector quantities are independent. Ex. the velocity north or south does not change the velocity east or west If 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.

Pythagorean’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 resultant If 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.

Trigonometric 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 side The resultant angle in the above problem is found : 110/55 = = = 64 degrees

Resolve 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 N VECTOR RESOLUTION is the process of finding the magnitude of the components in each direction.

Adding 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 components The 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

Subtraction of Vectors
To subtract vector B from vector A, reverse the direction of vector B and add it to vector A

Vector Products Two 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 B Ex 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

Problem Solving The 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

Summary Charts 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