• My series on making a Newtonian telescope
  • How Leon Foucault Made Telescopes

Guy's Math & Astro Blog

Guy's Math & Astro Blog

Monthly Archives: March 2020

Logs and Plagues

11 Wednesday Mar 2020

Posted by gfbrandenburg in Uncategorized

≈ 1 Comment

I just did the math in two ways: if each person infects 5 people who have never been infected, it only takes a bit more than 14 cycles from “patient zero” (whoever that was) to infect the entire living human population.

Obviously the real progress of an epidemic isn’t that simple.

Being a retired math teacher I figured this was a perfect case for using logarithms, so I did. (For me, that’s fun!) I went like this:

I’m trying to find n such that five to the nth power equals 7.5 billion, or in math-lingo,

5^n = 7.5*10^9

One takes the logarithms of both sides, and because of the wonderful properties of logs, I get n*log(5)=9+log(7.5) which we can solve for n by dividing both sides by log(5), obtaining

n = (9+log(7.5))/log(5), after which my calculator said n was about 14.1.

But if you have a cell phone you can confirm my result much more easily by asking it work out 5^14. I think you’ll find it’s about six billion; if you try 5^15 you’ll get an enormous umber, over 30 billion, which is much too high. We have only roughly seven and a half billion humans…

Recommended books on math

04 Wednesday Mar 2020

Posted by gfbrandenburg in Uncategorized

≈ Leave a comment

I’m copying part of this from Ali Kayaspour at Medium.com. I’ve read some of these but not all. A while ago I made a list of math-related books for my students to read; maybe I should resurrect it. Here is the link.

Continue reading →

Subscribe

  • Entries (RSS)
  • Comments (RSS)

Archives

  • November 2022
  • October 2022
  • August 2022
  • July 2022
  • June 2022
  • May 2022
  • April 2022
  • February 2022
  • January 2022
  • December 2021
  • October 2021
  • September 2021
  • August 2021
  • July 2021
  • June 2021
  • May 2021
  • March 2021
  • December 2020
  • October 2020
  • September 2020
  • August 2020
  • March 2020
  • February 2020
  • January 2020
  • December 2019
  • November 2019
  • September 2019
  • August 2019
  • June 2019
  • May 2019
  • January 2019
  • November 2018
  • October 2018
  • September 2018
  • August 2018
  • May 2018
  • March 2018
  • January 2018
  • November 2017
  • October 2017
  • September 2017
  • August 2017
  • July 2017
  • June 2017
  • May 2017
  • April 2017
  • February 2017
  • December 2016
  • September 2016
  • June 2016
  • May 2016
  • April 2016
  • March 2016
  • February 2016
  • January 2016
  • December 2015
  • November 2015
  • August 2015
  • July 2015
  • April 2015
  • March 2015
  • February 2015
  • January 2015
  • December 2014

Categories

  • astronomy
  • astrophysics
  • education
  • flat
  • History
  • Hopewell Observatorry
  • Math
  • monochromatic
  • nature
  • optical flat
  • Optics
  • Safety
  • science
  • teaching
  • Telescope Making
  • Uncategorized

Meta

  • Register
  • Log in

Blog at WordPress.com.

  • Follow Following
    • Guy's Math & Astro Blog
    • Join 48 other followers
    • Already have a WordPress.com account? Log in now.
    • Guy's Math & Astro Blog
    • Customize
    • Follow Following
    • Sign up
    • Log in
    • Report this content
    • View site in Reader
    • Manage subscriptions
    • Collapse this bar