top

A list of pages
 Top What's New

Introduction
What's New
Counting by powers of ten "ten, hundred, thousand, ..." (101, 102, 103, ...)
Counting to ten billion... on your fingers Counting by powers of ten, on fingers.
"What order of magnitude is ...?" game
Lots of dots
A million dots on one page
A dot for every second in the day with clock.
A dot for each day
How to simplify a number rounding, compacting, memorables, etc.
Rounding off a number simplifies it by creating zeros.
Rounding to an order of magnitude extreme rounding.
What is "order of magnitude"?
Exponential Notation sliding the decimal point.
Scientific Notation is exponential notation plus conventions.
How to write and speak the exponential notation
A few examples of exponential notation Not of much use.
On Being Approximate The what, why, and how.
Why be approximate?
Bounding uncertainty
Honesty in approximation
Fermi Questions Rough quantitative estimates.
Landmarks
A Pinocchio estimation game detecting implausible approximations
An experiment with mayonnaise
`Powers of Ten' scales
Scaling the universe to your desktop
Pm, Tm, Gm, Mm, km, m, Millimeters in your hands, um, nm
Deep understanding
If you can't explain it to a nine year old... then you don't really understand it yourself.
For children
Developing "deep" understanding
Probing near space with a flashlight
Exploring with teleportation Using imagination to generate questions
China is down over there... looking down through the earth
Over maps, envisioning the atmosphere
Earth's surface as a 20 x 25 Megameter rectangle
Round Earth, Tilted People
Visualizing Earth's Internal Structure a road trip going down
Atomic bonding
Getting a feel for big numbers
A feel for big numbers, with grains of salt
Only a breath away aka "Caesar's last breath"
Good descriptions
Knowledge you can work with...
Simple models
A ball's volume and area are 1/2 of its box's
When Length grows a little, Area grows a lot
The relative size of Earth, Jupiter, Sun (1 : 10 : 100)
Trig w small angles
Sphere
Resources
Search for Simplicity - Weisskopf a column.
The Back of the Envelope - Purcell a column.
On the Back of an Envelope - Triplehorn a column.
Scale of some things (with experimental frames)
Population , landmarks , other
People seconds
Time , landmarks , other
Length , landmarks , other
Area , landmarks , other
Volume , landmarks , other
Mass , landmarks , other
Energy , landmarks , other
Mass volume-density
Surface volume-density Packing surface in a volume.
Speed
Volume rate
Power , landmarks , other
Light-speed delay
Body Ruler
Measuring Angle and Distance with your Thumb

 A View from the Back of the Envelope Comments encouraged. - Mitchell N Charity

```Notes:
does not include all pages

Doables:
perhaps should include all pages... that was the point

History: