QUESTION
You may work on this homework on your own or discuss it with others. If you work throughquestions with others, be sure to turn in your own work, at the level at which you understandit. Do not simply copy answers from or for someone else. Questions such as these will showup on exams, so be sure to work to understand how to arrive at the answers.(1) (4 pts) Figure 1 depicts samples from four cylindrical tendons and all are composed primarily ofcollagen. Each has been clamped at both ends and a machine is used to gradually pull the ends inopposite directions (arrows) until the material yields (i.e., experiences internal damage).a. Which tendon sample(s) will probably require the most tensile force to cause internal damage?Why?b. Which tendon sample(s) will probably require the highest stress to cause internal damage? Why?c. Which tendon sample(s) will probably change length the most before experiencing internaldamage? Why?d. Which tendon sample(s) will probably have the highest elastic extensibility? Why?(2) (4 pts) Figure 2 shows the stress-strain curves under tension for four materials in their elasticregions. Recall that materials have the following properties:- A materialâs elastic modulus (E, âintrinsic stiffnessâ) determines how much stress (tensile orcompressive) on a material is required to induce a given strain [units of pressure]- A materialâs compliance determines how much strain results from an applied stress (complianceis the inverse of E) [units of 1/pressure]- A materialâs elastic strength is how much stress (tensile or compressive) is applied at the pointwhere the material yields (i.e., stops responding elastically to the applied stress) [units of pressure]- A materialâs elastic extensibility is how much strain results at the point where the material yields(i.e., stops responding elastically to the applied tensilestress) [units of length]a) List the materials in the order of their elasticmodulus (stiffness), from highest to lowest.b) List the materials in the order of their compliance,from highest to lowest.c) List the materials in the order of their elasticstrength, from highest to lowest.d) List the materials in the order of their elastic extensibility, from highest to lowest.(3) (4 pts) The picture below on the left shows an orb web. The red lines are called frame lines andthe blue lines are spiral threads. The frame lines hold the spiral threads in their proper place andprovide a structural framework. The spiral threads intercept flying insects; they slow the insectdown by absorbing its energy–stretching and not breaking.Which material in the stress-strain plot below (Fig. 3) would be best for a spiral thread? Why?Which would be best for a frame thread? Why?Fig. 3(4) (3 pts) Larger individual humans tend, not surprisingly, to have larger feet. But how exactlywould you expect the surface area of the bottom of an individualâs foot, which must support thedownward force (weight) of the standing person, to scale against body size? Two possibilities arethat scaling would simply be isometric or that scaling is allometric such that stress similarity ismaintained among feet of individuals of different sizes.a) Assuming full-body isometric scaling among individuals of different sizes, what would youpredict would be the value of the scaling coefficient (b) relating the surface area of thebottom of the foot to body height?b) Alternatively, assuming that scaling of feet is allometric such that stress similarity ismaintained among feet of individuals of different sizes (i.e., the stress on the bottom of thefoot is constant among individuals of different height), what would you predict would be thevalue of the scaling coefficient (b) relating the surface area of the bottom of the foot to bodyheight? Assume that the rest of the body scales isometrically.c) Use real data to see whether the actual relationship between human foot area and humanheight appears to be consistent with (a) or (b), above. To do this, go to the google docspreadsheet at https://docs.google.com/spreadsheets/d/19nlj0Ja0_CajV-8JA4qWRp4dZdBTM4eqKNirmkHrHk/edit?usp=sharing. This document is pre-populated with some real data Icollected, but to continually improve our data set, please add data from yourself (no need toadd your name, just your data!). Simply enter your sex, height, and the length, maximumwidth, and area of the bottom of your right foot (approximated as length X maximumwidth). All measurements should be made to the nearest tenth of a centimeter.You can then use Excel to fit a power function (scaling equation, Y=axb) to these data.Exactly how to do this will depend on your version of Excel. But the procedure will besomething like this:1.2.3.4.Select the two columns of numbers you wish to plot (Height and Foot Area).Click on the Charts tab & select Scatter plotSelect the resulting plot and click on the Chart Layout tab & Trendline subtab.Under Trendline Options, select Power & under Options (just to the left) click onâDisplay equation on chartâ and click OK.The equation of the power function fitted to your data should be displayed on your graphand you can now see whether the observed scaling coefficient appears to support thescaling relationship of (a) or (b) above.Give the scaling equation you get from Excel and explain your conclusion based on thescaling coefficient.
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