1PHY 2053 announcements: January 8, 2009•Textbook: College Physics I by Serway/Vuille soft cover with white background•Optional course packet (blue book): available at Target copy on Friday•Webassign: free for 11 more days please logon and enter the code from textbookemail me if you have problems with login1stassignment not for credit•Clickers: will start practice todayplease get one! you will need a few more defined units in PHY 2054 Units can be treated as algebraic quantities  add, subtract, multiply, divideTime remaining = 50 min – 20 min = 30 minArea = width x height = 4 cm x 5 cm = 20 cm2e.g., SI unit of area: meter2(m2)SI Unit of speed: meter/second (ms-1) To convey certain physical property of an object. Units of length: meter, foot, inches, lightyears…. SI -Systéme International (MKS=Meters-Kilograms-Second) CGS – Gaussian system (Centimeters-Grams-Second) US Customary (foot-slug-second)UnitsDimensions Length [L] Mass [M] Time [t] Temperature [T]Dimensional Analysis Technique to check the correctness of an equation. Both sides of equation must have the same dimensions  1 hour = 3600 sdimension t on both sides Area = width x height 4 cm x 5 cm = 20 cm2dimension L2 on both sidesSignificant Figures There is uncertainty in every measurement  A significant figure is one that is reliably known 3.1416 All non-zero digits are significant 13 2 significant figure 13.14 4 significant figures Significant figures = decimal places Zeros are significant when between other non-zero digits1004 4 significant figures after the decimal point and another significant figure1.00 3 significant figures can be clarified by using scientific notation1000 ? significant figures1.00 x 1033 significant figuresWhen multiplying or dividing two or more quantities, the number of significant figures in the final result is the same as the number of significant figuresin the least accurate of the factors being combined When adding or subtracting, round the result to the smallest number of decimal placesof any term in the sum If the last digit to be dropped is less than 5, drop the digit If the last digit dropped is greater than or equal to 5, raise the last retained digit by 1Rounding Off56.7 x 10.002 = 567.1134 = 56715.54 + 0.141 = 15.681 = 15.6815.54 + 0.146 = 15.686 = 15.69Unit ConversionsUnits can be treated like algebraic quantities that can “cancel” each other  See the inside of the text front cover for an extensive list of conversion factorsConvert inches to Centimeters:15.0 in2.54 cm1.00 inX=38.1 cmProblem Solving Summary Equations are the tools of physics Understand what the equations mean and how to use them Carry through the algebra as far as possible Substitute numbers at the end Be organized2Chapter 2: Dynamics The branch of physics involving the motion of an object and the relationship between that motion and other physics concepts Kinematics is a part of dynamics In kinematics, you are interested in the descriptionof motion Not concerned with the cause of the motionQuantities in Motion Any motion involves three concepts Displacement Velocity Acceleration These concepts can be used to study objects in motionVoyager’s path Robotic surgeryPosition Defined as the change in position f stands for final and i stands for initial May be represented as ∆y if vertical Units are meters (m) in SIfixxx∆≡ − Choose coordinate axes  In one dimension, generally the x- or y-axisDisplacementGraph: position vs time From A to B xi= 30 m xf= 52 m ∆x = 22 m The displacement is positive, indicating the motion was in the positive x direction From C to F xi= 38 m xf= -53 m ∆x = -91 m The displacement is negative, indicating the motion was in the negative x directionDisplacement examplefixxx∆≡ −Vector vs. scalar Vector quantities need both magnitude (size) and direction to completely describe them Generally denoted by boldfaced type and an arrow over the letter (x or ) + or – sign is sufficient for this chapter (for motion in 1 dimension) Scalar quantities are completely described by magnitude onlyxr3 Displacement is a vector. Distance is a scalar.Distance is not the same as displacement. Example: Throw a ball straight up and then catch it at the same point you released it The distance is twice the height The displacement is zero Speed vs. velocityAverage speed Average velocity==Total distanceTotal timeTotal displacementTotal time=dttxvaverage∆∆=vvtxxif∆−=vvscalar vectorSame average velocityDifferent speedUnits: meter/second (m/s)Average Velocity The straight line indicates constant velocity The slope of the line is the value of the average velocityConstant Velocity The motion is non-constant velocity The average velocity is the slope of the blue line joining two pointsNon-Constant Velocity∆x∆ttxvaverage∆∆=vv From A to B xi= 30 m xf= 52 m ∆x = 22 m From A to F xi= 30 m xf= -53 m ∆x = -83 mDisplacement exampleIf the time between successive snapshots is 1 second, Vaveragefrom A to B = ∆XAB/∆tAB= 22 m/1s = 22 ms-1Instantaneous Velocity:keep making smaller:∆t∆t∆xThe slope of the line tangent to the position-vs.-time graph is defined to be the instantaneous velocity at that timeAcceleration Changing velocity means an acceleration is present Acceleration is the rate of change of the velocity Units are m/s² (SI), cm/s² (cgs), and ft/s² (US Cust)  Vector quantity−∆==∆−fifivvvattt4Average AccelerationInstantaneous acceleration = slope of tangent of velocity-time