Lab Length and Length-Related Variables Assignment Instructions

ENGR 115 L AB : L ENGTH AND L ENGTH -R ELATED V ARIABLES A SSIGNMENT I NSTRUCTIONS I NSTRUCTIONS Lab assignments are intended to give you some ‘hands on’ experience in applying the concepts introduced in the course text. They are designed to get you out of your classroom or office and develop the skills of designing experiments and collecting data and then performing calculations, evaluating the results, and communicating your findings. Labs are more than just number crunching – they are about reflecting on what is both practical and technically sound engineering problem-solving. For each problem below, address the scenario presented and develop engineering solutions. Communicate your results using drawings, pictures, and discussion, supported by calculations developed using the Microsoft Equation Editor or similar tool. Submit your lab report in a single pdf file uploaded to the location provided in Canvas before the due date/time indicated. Each problem should be treated as a micro-report with a problem statement, calculations/work shown to support your solution, and a conclusion/reflection on your findings. P ROBLEMS 1. Given a square kilometer of land, how many cars can be parked safely there? Determine the appropriate spacing between cars and the width of drive lanes. Prepare a diagram showing your solution and write a brief report to your instructor discussing your assumptions and findings. Note that your plot of land does not need to be square – it just needs to have an area of 1 km2. 2. Obtain three to five different styles of shoes, including a woman’s high-heel style. For each shoe, make imprints of the floor contact surfaces. Determine the total area for each shoe, make an appropriate assumption concerning the weight of the person who is likely to wear each shoe style, and calculate the average pressure at the bottom of the shoe for each shoe style. What are your findings? What are your recommendations? Include drawings/pictures of your shoe prints and your calculations for area. Refer to your Moaveni text example 7.1. Recall that: pressure = force area 3. As explained in chapter 7 of the Moaveni text, the air resistance to motion of a vehicle is determined experimentally by placing it in a wind tunnel. The airspeed inside the tunnel is changed, and the drag force acting on the vehicle is measured. The experimental data is normally represented by a single coefficient which is called the drag coefficient. It is defined by the following relationship: C d = F d 1 2 ρV 2 A Page 1 of 3

ENGR 115 Where: C d = dragcoefficient ( unitless ) V = air speedinside thewind tunnel ( ft / s ) F d = measured dragforce ( lb f ) A = frontal areaof the car ( f t 2 ) ρ = air density ( slugs / ft 3 ) It was also explained in this chapter that the frontal area A is the frontal projection of the area and could be approximated simply by multiplying 0.85 times the width and the height of a rectangle that outlines the front of a vehicle when you view it from a direction normal to the front windshield. The 0.85 factor adjusts for rounded corners, open space below the bumper, and so on. Typical drag coefficient values for sports cars are between 0.27 and 0.38, and for sedans the values are between 0.34 and 0.5. a. What is the appropriate unit for C d if the preceding equation is to be homogeneous in units? Show all steps of your work. b. What is a typical value for air density? Cite your source. c. Measure the frontal area of a car. Tape a ruler or a yardstick to the bumper of your car. The ruler will serve as a scale. Take a photograph of the car and use any of the methods discussed in this chapter to compute the frontal area of the car. 4. For your semester design project, you have been provided a mouse trap car (MTC) kit by Doc Fizzix along with some additional tools. Over the semester, you will build your MTC and collect data that will be documented in future labs. When designing and building your MTC, you may use the parts provided in the kit, or you may purchase or design and fabricate your own parts. To start this project, you must research best practices for designing and building a MTC (be sure to cite your sources). First, take inventory of the parts in the kit and read the instructions provided with the kit. If you have not received your kit, you can access the details of the kit on this link DocFizzix . We will not build the MTC until week 3. Once you build your MTC, we will test it over 3 meters for speed/acceleration and the longest attainable distance/time. We will also calculate the coefficient of friction and efficiency of your MTC. In preparing for this assignment, research empirical qualitative data and reflect on the following questions (we are looking for research, not your own calculations): a. What length lever arm attached to the mouse trap will deliver energy from the spring to the axle to achieve the fastest time to travel 3 meters? b. Which length lever arm will allow your MTC to travel the longest distance? c. How will you design the lever arm to meet both of these criteria? d. What is an optimal length and width for your MTC body and where is the best location for the mouse trap? e. Include a diagram of your proposed MTC with your findings. Page 2 of 3