Efficiency of Man vs. Machine
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Questions and Answers

What is pressure defined as?

  • Force per unit area (correct)
  • Mass per unit area
  • Force per unit volume
  • Force per unit mass

    • What is the unit of pressure in medicine?

  • Pa atm (correct)
  • Atmosphere (atm)
  • Pascal (Pa)
  • Newton (N)

    • What causes atmospheric pressure?

  • Weight of the air in the atmosphere (correct)
  • Weight of the water in the air
  • Volume of the air in the atmosphere
  • Temperature of the air

    • Which formula correctly represents pressure?

    <p>$P = \frac{F}{A}$</p> Signup and view all the answers

    What is the atmospheric pressure in $N/m^2$?

    <p>1.0 $N/m^2$</p> Signup and view all the answers

    What is external work defined as?

    <p>A force moved through a distance</p> Signup and view all the answers

    In the formula $ΔW = F Δx$, what does $Δx$ represent?

    <p>Distance</p> Signup and view all the answers

    What condition must be met for external work to be done?

    <p>The force and motion must be in the same direction</p> Signup and view all the answers

    What is the formula for calculating the work done when climbing a hill?

    <p>$W = mgh$</p> Signup and view all the answers

    Which type of energy stored in the body is converted into external mechanical work?

    <p>Chemical energy</p> Signup and view all the answers

    When a person is walking up stairs, what type of work is being done?

    <p>External work</p> Signup and view all the answers

    What is the unit of pressure measurement used in medicine?

    <p>Height of a column of mercury (Hg)</p> Signup and view all the answers

    What is the peak systolic pressure in mm Hg?

    <p>120 mm Hg</p> Signup and view all the answers

    What is the density of mercury in $g/cm^3$?

    <p>13.6 g/cm^3</p> Signup and view all the answers

    What does 1 Pascal (Pa) equal to?

    <p>1 N/m^2</p> Signup and view all the answers

    In which unit is pressure measured in the metric system?

    <p>Both a and b</p> Signup and view all the answers

    What is pressure defined as in a gas or liquid?

    <p>Force per unit area in a gas or liquid</p> Signup and view all the answers

    Which activity has the highest efficiency according to the table?

    <p>Man (or Machine)</p> Signup and view all the answers

    For long-term efforts, the body's performance is proportional to which factor?

    <p>Maximum rate of oxygen consumption</p> Signup and view all the answers

    What is the efficiency of swimming underwater?

    <p>~3%</p> Signup and view all the answers

    Which of the following phases can only last about a minute?

    <p>Anaerobic phase</p> Signup and view all the answers

    What does the body split to supply energy for short-term power needs?

    <p>Energy-rich phosphates and glycogen</p> Signup and view all the answers

    Which of the following is NOT listed as a related factor for oxygen consumption?

    <p>Oxygen measured at tissues</p> Signup and view all the answers

    Which phase shows a rapid decrease in power produced with the duration of effort?

    <p>Anaerobic phase</p> Signup and view all the answers

    At what efficiency rate is shoveling performed?

    <p>17%</p> Signup and view all the answers

    What is the formula for the pressure under a column of liquid?

    <p>P = pgh</p> Signup and view all the answers

    What is the acceleration due to gravity in cm/sec² when calculating pressure in Dy/cm²?

    <p>980 cm/sec²</p> Signup and view all the answers

    If the height of a column of water is 10 meters, what is the pressure in D/cm²?

    <p>9.8 x 10⁵ Dy/cm²</p> Signup and view all the answers

    How do you calculate the pressure from a 12 cm column of mercury in Dy/cm²?

    <p>13.6 x 980 x 12</p> Signup and view all the answers

    What height of water will produce the same pressure as 120 mm Hg?

    <p>163 cm H2O</p> Signup and view all the answers

    What is the pressure of 10 m of water when using N/m² as the unit?

    <p>9.8 x 10⁴ N/m²</p> Signup and view all the answers

    What primarily happens to the additional heat generated in muscles during exercise?

    <p>It is removed by blood flowing through the muscle, conduction to the skin, and sweating.</p> Signup and view all the answers

    How is external work measured when a person rides a fixed bicycle?

    <p>By measuring the oxygen consumed.</p> Signup and view all the answers

    Which equation represents the efficiency (ε) of the human body?

    <p>$Efficiency (ε) = \frac{Work , done}{Energy , consumed}$</p> Signup and view all the answers

    At what power level is the efficiency of the human body the lowest?

    <p>Low power</p> Signup and view all the answers

    Which activity can increase the efficiency of the human body to 20%?

    <p>Cycling</p> Signup and view all the answers

    What is the formula for power (P) in terms of force (F) and velocity (V)?

    <p>$ P = F \times V$</p> Signup and view all the answers

    Study Notes

    Efficiency of the Human Body

    • The efficiency of man for several activities is shown in the table, with an efficiency of around 20% for activities such as cycling and rowing.
    • The maximum work capacity of the body is variable, with short-term efforts allowing for high power levels, but long-term efforts being more limited.
    • The body uses anaerobic and aerobic phases to produce power, with anaerobic power decreasing rapidly with duration and aerobic power being constant.

    Work and Power

    • External work is defined as a force moved through a distance (Δx), and can be calculated as ΔW = F Δx.
    • Power is the rate of doing work in time, and can be calculated as P = ΔW / Δt or P = FV, where V is velocity.
    • The human body can be considered as a machine in doing external work, with efficiency calculated as the work done divided by the energy consumed.

    Pressure

    • Pressure is defined as the force per unit area in a gas or liquid, and can be calculated as P = F / A or P = mg / Lw.
    • Atmospheric pressure is due to the weight of the air in the atmosphere, and is approximately 1.0 N/m².
    • Units of pressure include Pascal (Pa), N/m², dynes/cm², and mmHg.

    Measurement of Blood Pressure

    • Blood pressure is a common phenomenon in our daily lives, and is typically measured by a doctor as part of a physical examination.
    • Units of pressure in medicine include mmHg, with a typical systolic pressure being 120 mmHg.
    • Pressure under a column of liquid can be calculated as P = pgh, where p is density, g is acceleration due to gravity, and h is height of the column.

    Examples

    • Example 1: Find the pressure of 10 m of water in Dy/cm² and N/m².
      • P = pgh = 980000 = 9.8 x 10⁵ Dy/cm²
      • P = pgh = 1000 x 9.8 x 10 = 9.8 x 10⁴ N/m²
    • Example 2: Calculate the systolic pressure in Dy/cm² and N/m².
      • P = p Hg g h Hg = 159936 = 1.6 x 10⁵ Dy/cm²
      • P = p Hg g h Hg = 13600 x 9.8 x 0.12 = 1.6 x 10⁴ N/m²
    • Example 3: What height of water will produce the same pressure as 120 mm Hg?
      • P (120 mm Hg) = pgh = (13.6 g/cm³)(980 cm/sec²)(12 cm) = 1.6*10⁵ dyne/cm²
      • h = 163 cm H2O.

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    Compare the efficiency of humans in various activities such as swimming, shoveling, and more with machines. How efficient are we?

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