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September 4, 2023

US 1956 stamp in honor of Labor Day Today, September 4, 2023, is Labor Day in the United States. This holiday in honor of the American worker is observed on the first Monday in September, making this a three day holiday when combined with the Saturday and Sunday of the weekend.

Congress passed an act on June 28, 1894, making Labor Day a legal holiday.[1] However, prior to that time, many U.S. states had recognized a Labor Day holiday, the first Labor Day holiday being celebrated on Tuesday, September 5, 1882, in New York City.[1]

The present day mantra for Labor Day might be Rihanna's Work in which the word, work, is often repeated.[2].

(1956 United States postage stamp in honor of Labor Day, issued on September 3, 1956. Wikimedia Commons image by Karen Horton.)

The conflict between employers and employees and its concurrent income inequality is recently framed in the concept of the one-percenters. Income inequality has been with us since before medieval fiefdoms, but it flourished during the Industrial Revolution. A dramatization of this in the early 20th century is the 1927 silent film, Metropolis, directed by Fritz Lang (1890-1976).[3-4] This film, one of the first science fiction films, just entered the public domain in the United States; but, to illustrate the flawed state of copyright law, it's still under copyright in the European Union until 2046. This 120 term limit for copyright seems excessive to all except politicians.

One other theme of Metropolis is that man has been subjugated by his technology (see video clip), something many of us feel when being besieged by email messages and text messages long after working hours.

Video Downloads

• MP4 video file (Metropolis_01.mp4, 5.1 MB)
WebM video file (Metropolis_01.webm, 0.75 MB)
MOV Video file (Metropolis_01.mov, 4.5 MB)

intuitively observed by any child pulling a sibling on a wagon or snow sled, work is related to the pulling force needed and how far you need to travel. French philosopher, René Descartes (1596-1650), realized this when he wrote in an October, 5, 1637, letter to Dutch physicist, Christiaan Huygens (1629-1695), "Lifting 100 lb one foot twice over is the same as lifting 200 lb one foot, or 100 lb two feet." German polymath, Gottfried Leibniz (1646-1716), concurred in 1686 by writing that "The same work is necessary to raise body A of 1 pound to a height of 4 yards, as is necessary to raise body B of 4 pounds to a height of 1 yard."

Work W is defined in physics as the scalar product of a force F acting over a distance L. Since it's a scalar product of vectors, if the direction of force and distance are not aligned, we need to multiply by the cosine of the angle θ between their directions; viz., W = F·L cos(θ). The newton is the unit of force, making the unit of work to be a newton-meter. The SI unit of work, the joule, is also the same unit for energy.

There's a connection between work and energy, as seen in their having the same units. Energy is work done over time. Net positive work increases the kinetic energy of a particle, while net negative work will cause a decrease; and, the longer the work is applied, the greater the energy change. The applied work is equal to the change in energy,
W = ΔEk

In the late 18th century, Scottish engineer, James Watt (1736-1819), quantified work as it's expended over time. Today's unit for this quantity, power, is the newton-meter/second, which is called a watt in his honor. In Watt's time, horses were a primary source of power for many things; so, Watt's unit of power was the horsepower, the power needed to lift the weight of a man (75 kilograms) to one meter in one second (see figure). In today's units, a metric horsepower is about 735.5 watts.

Metric Horsepower

Illustration of the metric horsepower as the power needed to lift 75 kilograms one meter in one second. Automobile manufacturers delight in using horsepower as a measure of their engine performance. (Modified Wikimedia Commons image by Sgbeer. Click for larger image.)

As we celebrate Labor Day, foremost in our minds should be the workers who do real work; namely all the tradesmen, construction workers, service workers, and so on. On a second tier are all those who sit comfortably at a computer terminal all day in a climate controlled office; and, yes, that includes me. How much work is actually done by pushing keys on a computer keyboard? Estimates of the force and stroke needed to enter a character on a keyboard can be found on the Internet,[5] and this gives the work needed to enter a keyboard character. Combine this with an average typing speed (characters per minute, cpm, and characters per second, cps) gives an estimate of the power expended in continual typing, as shown in the following table.

Keyboard Keypress Power
Quantity Value Units
Force 5.5 N
Stroke 2.0 mm
Stroke 0.002 m
Rate 225 cpm
Rate 3.750 cps
Duration 0.267 seconds
Power 0.041 watt

Since the basal metabolism of a human is about 60-75 watts, we see that keyboard entry is roughly equivalent to being a couch potato.


  1. History of Labor Day, U.S. Department of Labor Web Site.
  2. Rihanna, "Work, ft. Drake (Explicit Lyrics), Vevo Video on YouTube, February 22, 2016, also found at Rihanna, "Work, ft. Drake (Lyrics), YouTube Video by Lily Torres Reyes, February 24, 2016.
  3. Metropolis (1927, Fritz Lang, Director) on the Internet Movie Database.
  4. Metropolis (1927, Fritz Lang, Director), YouTube Video by All Time Classics, Aug 31, 2022.
  5. Das Keyboard Blog.

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