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Critical thinking

Critical thinking. (for engineering). Exercise. By timing the fall of a barometer , a friend measures the height of a 20-story building to be 71 feet. . Is this estimate reasonable? If so, explain why. If not, give a cogent reason and suggest possible mistakes. Evaluating a result.

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Critical thinking

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  1. Critical thinking (for engineering)

  2. Exercise By timing the fall of a barometer,a friend measures the height of a 20-story building to be 71 feet. Is this estimate reasonable? If so, explain why. If not, give a cogent reason and suggest possible mistakes.

  3. Evaluating a result What are some tests for a result or formula?

  4. Example: falling barometer t Dimensions? Boundary and initial conditions? Behavior? Dependence on parameters? Special cases? Assumptions? h

  5. Exercise: drag on a body FD = drag force [F] CD = drag coefficient [-] r = fluid density [M/L3] U= fluid velocity [L/T] A = cross-sectional area

  6. Exercise: beam deflection y = deflection x = position on beam L = beam length P = load (force) E = Young’s modulus I = moment of inertia

  7. Exercise: contaminant plume L = plume length V = groundwater velocity T1/2 = half-life of contaminant C0 = source concentration Cs = max. allowable concentration

  8. Exercise: rating curve Which curve best represents river discharge vs. river stage?

  9. Exercise: fruit flies in a jar Which is a better model? N = number of fruit flies at time t N0 = initial number r = reproduction rate K= constant

  10. Dimensional analysis Often one can predict the form of an answer simply by considering the dimensions of the parameters. • Approach: • List all parameters (including unknown) and their dimensions. • Determine the number N of parameters and number M of • dimensions. • Determine the number of dimensionless groups (N-M). • Pick any M variables that do not form a dimensionless group • and use them to make the other parameters dimensionless.

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