From wsanford@wsanford.com Sun May 30 13:25:22 2004 Date: Sun, 30 May 2004 13:10:10 -0400 (EDT) From: Walter Sanford To: Walter Sanford Subject: Gr8PS Brainstorming re: Mousetrap-Propelled Vehicle Project > Misc. MPV To-Do's (x) - Record Trial 2 distances from Data & Calc sheets (x) - Select MPVs to keep (?) Patrick, (yes) Nicholas, (no) Elliot, (yes) Baura.... (x) - Digital pix of ALL students w. MPVs. http://www.wsanford.com/~wsanford/gr8ps/mpv/SMS-2004/ - Re-take dig. pix of mousetrap (set) to illustrate third-class lever; use Photoshop to add text labels. [See Disk 5 & 6.] - Add a second mousetrap (w. longer lever arm) to the "Tylernol-coffin" MPV; use to demo performance advantage. (x) - Meas. mass of mousetrap, CDs, etc. * Tylernol-coffin = 523.8 g (or .5238 kg) total mass * Mousetrap = 23.5 g * CD-ROM = ~15.9 g, ~12 cm diam., ~1.5 cm (~15 mm) inner diam. 4.75" diam., 9.5/16" inner diam. * No. 2 Rubber One-hole Stopper (wheel mount) = 8.5 g * No. 2 Cork One-hole Stopper = 1.2 g * green army truck = ~81 g - Set up tests for rotational inertia: diff. cars; same wheel-axle assembly w. diff. wheel-spacing. Borrow Betsy's calipers. - Experiment w. force probes. (x) Check Vernier book for info. re: force probes. [See supplemental e-mail, "Physical Science w. Computers."] (x) - Experiment with LoggerPro and motion detector. See "Physics with Computers": No. 2 - Distance vs. Time (velocity); No. 3 - Velocity vs. Time (acceleration). (x) - Contact Linda Chin &/or Myra Thayer re: copy of "Logal Physics" - Contact Physics teachers at WPHS, (x) MVHS, &/or (?) Bryant Alt. HS re: ticker timers. [MVHS Physics: Shapiro, Mr. Avi J.; Louie, Sonny; Sabatier, Charles H. Bryant Alt. HS Physics: Robert Mead + Ray Albers (RESEED), albersr@bellatlantic.net] > Load "Mousetrap Vehicle Analzer" CD-ROM software on all laptops. Experiment with "Test" data (see graphs, spreadsheet, etc.) to infer properties that enhance vehicle performance. > Weight is acceleration due to the force of gravity, right? If so, then measure force (F) in Newtons and calculate weight. > See Grade 8 Math curriculum re: sequence of topics. -- > MPV Project IS the unit test for Red Lab Guide (authentic assessment). Ditto for "The Atom Project" (green guide) and insulate &/or cool cup of boiling H20 (tests understanding of concepts related to insulation & heat transfer, yellow guide). > Misc. notes from mtg. w. Lew Wetzel + follow-up questions: - As spring is loaded, force steadily increases. - Regardless of length of lever arm, spring has the same potential energy when loaded (test empirically). - Is it possible to calculate the mass threshold beyond which an MPV will not roll? > Google search: "torsion spring" e-mail Doc Fizzix re: the following questions (?) - "Printable Mouse Trap Racer Experiments" - incl. TAK w. sample problems? > Mousetrap Science Tools and Software http://www.docfizzix.com/mouse-trap/software-tools/index.shtml * The Torsion Wheel * Mousetrap Vehicle Analyzer (software) - available when? > Mouse Trap Powered Vehicle Products http://www.docfizzix.com/mouse-trap/index.shtml "Doc Fizzix Extras: games, T-shirts, and more!" - available when? > Ultimate Distance Mousetrap Vehicle kit (pulley-driven car) Item Number: K-150-DF price: $46.95 Alden J. Balmer (a.k.a., Doc Fizzix) McNeil HS Round Rock Independent District Round Rock, TX Supplies to order from Doc Fizz: - 1/8" brass tubing (lever arm) - 1/4L sink washer - SEA #10 metal flat washer - 3/16" brass tubing (axles) - graphite powder - ? glue ? Mousetrap [-Propelled] Car [Vehicle] Project (MPV Project) - Two cars &/or two options: distance; speed. Create student guide entitled ...
How to Build a Better Mousetrap ... Propelled Vehicle
Include sections that correlate with all red lab guide activities: - Average speed (distance cars) - Acceleration (speed cars) - The Force of Friction [substitute MPV Project-related activity(ies) for student-designed investigation] - Newton's Laws of Motion (series of demos & mini-activities) - Work: done to load mousetrap spring; done by spring to drive axle. - Power: lower-powered (distance cars); higher-powered (speed cars) -- How does Newton's First Law of Motion guide our thinking re: MPV design? -- How does Newton's Second Law of Motion guide our thinking re: MPV design? F = m x a a = F/m Force is constant (PE of mousetrap spring is constant); mass and acceleration are inversely related (larger mass, smaller acceleration; smaller mass, larger acceleration). Google search: "What is a Newton?" Definitions of newton on the Web: http://www.google.com/search?hl=en&lr=&ie=UTF-8&oi=defmore&q=define:newton "The unit of force required to accelerate a mass of one kilogram one meter per second per second." www.allmath.com/glossary.asp Therefore, 1 Newton is the minimum force req'd. to accelerate an MPV w. a mass of 1 kg (1,000 g). Compare tot. dist. vs. tot. time -- is ratio 1:1? -- [Mount second door handle (located near hinges) at same height as first.] A door is a second-class lever. Is work done to open a door? Yes! Force applied (push or pull) and door moves in same direction as force. Demo/observe force-distance trade-off. Google search: door + lever + class - good illustrations http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/lever2.htm http://www.planet-science.com/under11s/index.html?page=/under11s/levers/ http://www.technologystudent.com/forcmom/lever1.htm - good example calculations http://www.tpub.com/machines/1b.htm [Do "lever math" for two door handles: amount of force req'd. to open door for Handle 1 & 2. Could be tricky! Search for the following text string: "The same general formula applies for the second class of levers; but you ..."] "Pull-Ease" Increase mechanical advantage by utilizing pulleys? http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/ machine6.htm "The effort distance and resistance difference [?distance?] change but not the amount of work. The amount of work does not change." www.math.com Definition, factor: One of two or more expressions that are multiplied together to get a product. CONSTRUCTION TIPS Main Components: - Body - Wheel & axle system - Drive train: mousetrap; lever arm; string; drive axle Tools: - Safety goggles - Black & Decker Workmate http://www.blackanddecker.com/Search/Search.aspx?SearchTerm= workmate&SSection=PG - mini-vise (or Workmate) - Clamps or C-clamps - Small drill press &/or ?Dremel Kit? - B&D mitre box - X-acto knife & saw w. mitre box - hacksaw or pipecutter (cutting Cu tubing) - wire cutters - calipers or snap gauge - SuperGlue * The pulling string must be perpendicular to the drive axle radius for maximum performance at the start. The "perpendiculator" -- -- | \/ | * Lever arm should not extend past the drive axle when in the lowered position (good graphics on p. 112; check website) * The lever arm should be long enough to reach the drive axle -- no longer or shorter. * The string should "just" reach the drive axle or be a little shorter. * (p. 132) As a general rule of thumb, the string should be 2x the lever length or shorter. * The axle hook should not be longer than 1/8". * Attach lever arm extension to torsion spring side of snapper. Misc. notes from book... p. 31 convert mass to weight Weight(Newtons) = m(kg) x 9.8m/s(2) p. 60 Experiment: Finding the center of mass p. 63 Rotational inertia p. 67 Lab #4 - As the wheels turn p. 70 Step 2: Calculate the weight of your hanging mass by dividing by 1000 and multiplying by 9.8. E.g., 1 oz. fishing sinker = 28 g, or .2744 N p. 71 Formula for rotational inertia p. 73 Formula for rotational inertia (for wheel or axle system) p. 74-75 ENERGY key idea (p. 75). When building an MPV, the objective is to TRANSFORM the stored energy [PE] of the spring into forward motion [KE]. By reducing or [nearly] eliminating friction, your vehicle will be more EFFICIENT (at converting energy into motion). p. 76 ENERGY: Capacity to do work. Potential energy [PE]: the amount of stored PE is the same as the work req'd. to wind spring. W = F x d pp. 90-91 Power output, power stroke pp. 92-93 Mechanical advantage: a mousetrap is a third-class lever. p. 95 Tips re: increasing mechanical advantage [MA] p. 96 Wheel-to-axle ratio - change mechanical advantage p. 99 As a general rule of thum, a higher power rating means less EFFICIENCY and less overall travel distance. An MPV designed for distance should have a lower power rating. p. 100 Formula No. 3: Pulling Distance = Length of string x radius(wheel)/ radius(axle) p. 102 Ideal Mechanical Advantage IMA = r(wheel)/radius(axle) or d(MPV pulled by lever arm)/d(string on axle) p. 104 Lab No. 8 Conserving Energy - complex, involving many tedious variables Efficiency = KE/PE x 100 - typo on p. 105 (mistakenly refers to Lab No. 3); should refer to Lab No. 2, Predicted Travel Distance. Predicted Travel Distance = Total PE/Rolling Friction p. 110 Torque (door knob demo) -- Need to integrate student measurement of more physics (motion) parameters. Students measure ... Misc. notes re: data tables: Table w. 2 rows, 2 col. (data for calculating average speed): Total Distance (m) | | Total Time (sec) | | Table w. 2 rows, 11 col. (data for calculating acceleration/deceleration): Distance (m) | 1 | 2 | 3 | 4 | 5 | 10 | 15 | 20 | 25 | 30 | [?40, 50?] Time (sec) | | | | | | | | | | | *Note: Record times to the nearest hundredth of a second. If necessary, convert min & sec to seconds. ... & calculate the following: - average speed average speed (s) [or velocity] = total distance (d) / total time (t) [more appropriate measurement for speed cars?] - acceleration/deceleration (formula?) acceleration = delta-velocity (or delta-speed) / time a = delta-v / t ? - momentum ? (p = m x v) - work (J) = F (N) x d (m), where: "F" is measured with a spring scale hooked at the end of mouse trap spring/lever (or extension arm); "d" is half the circumference of a circle with a radius equal to the length of the trap spring/lever. C = pi x D or pi x 2r; semi-circle = C/2 More simply, semi-C = pi x r ? - power (Watts) W = work (J) / time (sec) > Revise D&C sheet to include the following items: - sample equations for Trial 1 (students simply fill in their data & solve) - time for "snapper" to close (req'd. for "power stroke" power calc.) Project Descriptor: The "mouse trap car" project -- an authentic learning activity in which students have the opportunity to demonstrate the creative problem-solving skills required to design & build a self-propelled car that shows mastery of their understanding of the (laws of) physics of motion (the culminating activity for the red Student Lab Guide). Grading Criteria: > Car must be self-propelled (perhaps the most important grading criterion). Merriam-Webster Online Dictionary propel: to drive forward or onward by or as if by means of a force that imparts motion [Mouse Trap Propelled Car Project] energy: the capacity for doing work There will be two trial runs: 1. Under its own power, the car must cross the starting line by at least the length of the car; 2. During Trial 2, the car must roll farther than it did during Trial 1. > The car must be modified in some way between Trial 1 & 2 (to improve its performance). Modest criteria for judging the performance of the students' cars (the same criteria used by all Grade 8 Science teachers). Project Timeline & Milestones: 3- to 4-week period 1 - Day 1: announce project as culminating activity - Day 2: distribute grading rubric (half-sheet paper) plus data & calc sheets; online research - Day 5: mechanical drawing plan & mtls. list due 2 - build/test cars 3 - Day 1: Trial 1 4 - Day 1: Trial 2 Grading Rubric (100 points total) 10 - plan, mtls. list (5 + 5) 30 - Trial 1 20 - Trial 2 30 - data & calc (15 for T1 + 15 for T2) 10 - "fudge factor" for originality of design, creativity, etc. Use Likert scale: 0-4 (below avg.); 5 (avg.); 6-10 (above avg.) Extra credit performance incentives: = or > 5 m = 5 pts.; 10 m/10 pts; 15 m/15 pts; 20 m/20 pts. Misc. To-Do's > revise data & calc sheet > physics teacher (or RESEED guy from Mount Vernon area) re: peer review of procedure x - Google search: physics + "mouse trap car" - Is "power" time technically time for lever to flip? Yes (I think). If so, then revise data & calc page accordingly. > set up MPV calculator Web pages or spreadsheet Misc. Notes > Victor Woodstream Corp. Lititz, PA, USA www.victorpest.com - Victor(R) Snap Traps: "M150 - Traditional Mouse Snap Trap" > Google search: victor + mousetrap Doc Fizzix - Mousetrap Powered Vehicles Mousetrap Project Products http://www.mousetrap-cars.com/mousetrap/doc_fizzix_products.htm http://www.docfizzix.com/ > String/axle connection - use either pin in axle or hole in axle (thread string thru eye-hole) > empirically test advantage of small (better for distance?) or large rear axle (better for speed?) > Is the force req'd. to pull the car w/o the mousetrap called the "resistance force?" > howstuffworks - How Force, Power, Torque and Energy Work http://science.howstuffworks.com/fpte.htm - Levers and Torque http://science.howstuffworks.com/framed.htm?parent=fpte.htm&url= http://www.comfsm.fm/~dleeling/physics/torque.html > Assessment Ideas: - label diagram of mousetrap car (courtesy Dr. Fizzix) to show six (6) simple machines: (x)lever; pulley; inclined plane; wedge; (x)wheel & axle, (?)screw A mousetrap is a third-class lever. Need explaination of location of key components of levers (fulcrum, etc.) -- - take home spring scale - design series of speed vs. distance demos, featuring variety of vehicles illustrating different physics (dynamics) principles - What do you call the force req'd. to pull the vehicle w/o mousetrap? Resistance force? - check w. HS physics dept. re: borrowing ticker timers or photoelectric timers - balanced & unbalanced forces: Will car roll if N-m string torque is greater than N-m axle torque? What about mass of car & friction? - use pulleys to increase mechanical advantage? Study graphics from "howstuffworks" pulleys & levers: rear axle - double pulley - single pulley - moustrap - front axle Torque test: dumbbell (correct spelling has two "b"s) versus barbell How much pulling force req'd. to roll each? - make connections with work lab: W = F x d Motion must be in the same direction as force. - carrying a box, not a force - pushing against a wall, not a force Definitions... Main Entry: mousetrap (one word, according to Merriam-Webster Online Dictionary) Main Entry: dynamics Pronunciation: dI-'na-miks Function: noun plural but singular or plural in construction 1 : a branch of mechanics that deals with forces and their relation primarily to the motion but sometimes also to the equilibrium of bodies Mousetrap-Propelled Vehicle (MPV) *find copy of longer, detailed guide from 2002-2003 (last year) Official Website: http://www.edroth.com/ Rat Fink cartoon art by Ed "Big Daddy" Roth http://www.eskimo.com/~bpentium/ratfink.html http://www.ratfink.org/ >> Buy Rat Fink stickers & t-shirt no pre-fab wheels! Cars must display a nickname, e.g., The Mean Green Machine (MGM) Potential moustrap car names: Transformer P-K (potential-kinetic) DynaMix or DynaMX SanforDynamo SanforDominator TorqueMaster 2000 San4D LDX (long-distance extreme) drofnasCAR - ("NASCAR" = National Association for Stock Car Auto Racing, Inc.) ================================================================= Walter Sanford, Director Carl Sandburg Middle School Center for Sky Awareness 8428 Fort Hunt Road Sandburg Planetarium Alexandria, VA 22308 Fairfax County Public Schools Work: 703-799-6169 -6197 (fax) E-mail: wsanford@wsanford.com Home: 703-765-9392 AMS Project ATMOSPHERE Atmospheric Education Resource Agent SCSA, Geosystems, & Camp T-Equity - URL: http://www.wsanford.com/ =================================================================