The Physics
Opus in profectus

International System of Units

search icon



  1. Write something.
  2. Write something.
  3. Write something.
  4. Complete the following puns based on the SI prefixes.
    1. 10−15 boy = 
    2. 10−12 door = 
    3. 101 cards = 
    4. 10−6 fish = 
    5. 1021 piccolos = 
    6. 2 × 103 mockingbirds = 
    7. 106 pains = 
    8. 101 millipedes = 
    9. 1012 microphones = 
    10. 1012 pins = 
    11. 101 rations = 


  1. Identify an everyday object or event that has, to the nearest order of magnitude, …
    1. a length of about 1 m (or height or width or thickness)
    2. a mass of about 1 kg
    3. a duration of about 1 s
    No "wise guy" answers like a meterstick, a one kilogram bag of flour, or the time between ticks on a clock.


  1. As the saying goes, "a journey of a thousand miles begins with a single step". What Midwest American city (or West Coast suburb) is equivalent to a single step in a much shorter journey of only a thousand steps? (Hint: a journey of a thousand steps is best described as a walk.)
  2. According to Classical Greek legends, Helen (daughter of Leda, queen of Sparta, and Zeus) was the most beautiful woman in the world. When Helen reached marriageable age, all the greatest men in Greece courted her. Acting on the advice of Odysseus, Helen's stepfather got all the suitors to swear that they would support the marriage rights of the successful candidate. He then settled on Menelaus to be the husband of Helen. She lived happily with Menelaus for a number of years, and bore him a daughter, Hermione. After a decade or so of married life, Helen was abducted by (or ran off with) Paris, the son of King Priam of Troy. Menelaus called on the other suitors to fulfill their oaths and help him get her back. As a result, the Greek leaders mustered the greatest army of the time and set off to wage what became known as the Trojan War. The English dramatist Christopher Marlowe described Helen as having the "face that launched a thousand ships". Using the "Helen" as the standard of beauty, how beautiful would one have to be…
    1. to launch a single ship?
    2. to "launch" a car?


  1. Tom Duff at Bell Labs is reported to have said that "π seconds is a nanocentury". Show that he was more or less correct. (The nanocentury was invented at IBM as a software design objective — never let the user wait more than a few nanocenturies for a response.)
  2. The mathematician John von Neumann is reputed to have said that a lecture should never last longer than a "microcentury". How long is this in more familiar time units? Justify your answer.