HONORS PHYSICS!Good morning! Please…• Take out your homework to be checkedUse the graphs shown to answer thewarm-up question:1. Draw a sketch of the a vs. t graph during the time t = 0-4 seconds.2. Develop an x as a function of t equation for t = 7- 15 seconds(use equation xf = xi + vit + ½ at2)3. Develop a v as a function of t equation for t = 7-15 seconds(use equation vf = vi + at) 1.
HOUSEKEEPING!**LAST DAY TO MAKE UP TESTS, QUIZZES, HOT TASK, HAND IN LATE WORKIS 10/26***• Physics in the news• Catapults coming soon! Launching is on 10/26 • Rules/grading are posted online • For homework today: • A status update on your progress • Your plans for how you will construct & test your catapult• Coming up… • Formal lab report will be due Monday 10/24 • Quiz will be Monday 10/24• Due next class: vocab
HOMEWORK SOLUTIONS FOR BOOK PROBLEMS:Pg. 41 problems 14, 15; pg. 42 problems 33-3514. Can an object be increasing in speed while acceleration is decreasing? Think vectors: is acceleration a vector? Is speed a vector? Acceleration is a vector. Speed is scalar. So, acceleration can be decreasing (becoming more negative), while speed is increasing (since it could be getting more negative also, but speed does not have direction, so it is getting bigger!)15. As a freely falling object speeds up, what is happening to its acceleration due to gravity? Does it increase, decrease, or stay the same? As an object speeds up, its acceleration due to gravity remains the same – it always acts downward at 9.81 m/s233. Time = 2.6 s34. Xf = -60 m/s (if you use -9.81 m/s2 – it will be positive if you use +9.81 m/s2)35. a) time = 8.81 s b) vf = -86.3 m/s
• In this lab, we will use a dot timer to calculate gravity in two ways G WHIZ LAB • Graphically - but how? Yf = yi + vit + 0.5at2 • Using equations: Which can be simplified to… • What equation can you use to calculate gravity if given: Yf = 0 + 0 + 0.5at2 • Yi = 0 m • Yf = gathered data Yf = 0.5at2 • Vi = 0 m/s • Vf = ? • a = ? (what we are solving for) • t = gathered data
FORMAL LAB REPORT WRITE-UP• Lab report should be in paragraph form, broken up into sections as required• Sections to include (which are listed on rubric) • Problem definition • What question(s) are you trying to answer? • Include any preliminary observations or background information about the subject • Experimental design • Data presentation • Conclusion & discussion
PROBLEM DEFINITION• Statement of the problem• Hypothesis • What do you think the value of acceleration will be? • Do you think the number of washers (or the mass) attached at the end will make a difference in the value of acceleration? Why or why not?• Identify Independent variable: the variable we are in control of changing• Identify dependent variable: the variable we are measuring – its results “depend on how the experiment goes”
EXPERIMENTAL DESIGN• What materials are used in this lab?• What safety notes need to be considered?• How many trials were done?• Were there any constants? Was there a control?• Explain the procedure in enough detail so that someone could repeat the experiment
Time (1/60 sec) Distance (mm) 1 2 Data Presentation 2 3 1.5 1.5 Distance (cm) vs. Time Graph 4 2 250• Clear data tables with title, 5 2.5 6 3 labels and units 200 7 3.5 Distance (cm) 8 4 150• Sample calculations included 9 3 10 3 100• Equations used are provided 11 3.5 50• Graphs with title, labels, and 0 units 0 50 100 15 Time (1/60 seconds) • Dependent variable is always on the y axis, dependent Velocity vs. Time Graph for Ticker Tape 200 variable is on the x axis Lab 180 y = 1.312x 160 R² = 0.936 140 Velocity (cm/sec) 120 100 80 60 40 20 0 0 20 40 60 80 100 120 140 160 Time (1/60 seconds)
CONCLUSION AND DISCUSSION Lab questions:• Lab questions are answered 1. Was there a difference between the sufficiently accelerations for the different masses? • Answered in a way so that the Explain why this may occur. reader does not have to know the 2. What is the acceleration of gravity on the question being asked when moon? Why is it different than on the Earth? reading your response. 1.6 m/s2! Gravity is the attraction between any two objects & is larger for more massive objects 3. Did your graphs show a constant acceleration? Explain. 4. Calculate and explain what is represented by the area under your velocity vs. time graph. 5. Would you expect your calculated values for acceleration to be higher than, equal to, or less than the accepted value for accelerated due to gravity (9.8 m/s 2)? Why? Calculate the relative error. Relative Error = your result– accepted value (9.80) x100 accepted value (9.80)
CONCLUSION AND DISCUSSION• The lab conclusion is discussed • What effect did the independent variable have on the dependent variable? • Support your conclusion by referring to at least two references to graphs and tables to show reader how you reached your conclusion • Validity of experiment is discussed: • Was there anything that you noticed while performing the lab which could have affected your data? • Were the number of trials adequate? • Compare your results to your hypothesis – were the results what you thought they would be? Why or why not?• Possible sources of error are identified & suggestions are made to reduce error• Ideas for improvvement and extension are provided.• Wrap up conclusion, make connections to everyday situations.