Efficiency of Man vs. Machine

Questions and Answers

What is pressure defined as?

Force per unit area

What is the unit of pressure in medicine?

Pa atm

What causes atmospheric pressure?

Weight of the air in the atmosphere

Which formula correctly represents pressure?

$P = \frac{F}{A}$ Signup and view all the answers

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

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

What is external work defined as?

A force moved through a distance Signup and view all the answers

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

Distance Signup and view all the answers

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

The force and motion must be in the same direction Signup and view all the answers

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

$W = mgh$ Signup and view all the answers

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

Chemical energy Signup and view all the answers

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

External work Signup and view all the answers

What is the unit of pressure measurement used in medicine?

Height of a column of mercury (Hg) Signup and view all the answers

What is the peak systolic pressure in mm Hg?

120 mm Hg Signup and view all the answers

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

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

What does 1 Pascal (Pa) equal to?

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

In which unit is pressure measured in the metric system?

Both a and b Signup and view all the answers

What is pressure defined as in a gas or liquid?

Force per unit area in a gas or liquid Signup and view all the answers

Which activity has the highest efficiency according to the table?

Man (or Machine) Signup and view all the answers

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

Maximum rate of oxygen consumption Signup and view all the answers

What is the efficiency of swimming underwater?

~3% Signup and view all the answers

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

Anaerobic phase Signup and view all the answers

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

Energy-rich phosphates and glycogen Signup and view all the answers

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

Oxygen measured at tissues Signup and view all the answers

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

Anaerobic phase Signup and view all the answers

At what efficiency rate is shoveling performed?

17% Signup and view all the answers

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

P = pgh Signup and view all the answers

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

980 cm/sec² Signup and view all the answers

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

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

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

13.6 x 980 x 12 Signup and view all the answers

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

163 cm H2O Signup and view all the answers

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

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

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

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

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

By measuring the oxygen consumed. Signup and view all the answers

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

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

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

Low power Signup and view all the answers

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

Cycling Signup and view all the answers

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

$ P = F \times V$ 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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Description

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