How low can you see that the earth is curved

At how low an altitude does the earth look like a disk, in other words, from how low does a line from the horizon to your eye trace out the surface of a cone (with angle a shown from the centre) ?

Surprisingly low. The depression of the horizon below level is noticable from an altitude as low as 218m. (Lysterfield Lake trig point 37°56'31" S 145°16'06" E, Elevation 218m)

View looking south east, the faintly visible Strezleki ranges are level with the line

View looking north west, the horizon is below the string

Looking east, the horizon is below the two tape markers

Looking west, the horizon is just below the two tape markers

The average depression was 7mm at a distance of 147cm

a = sin (a) for small a

a = 0.7/147 = 0.00476

r = 2h/a^2

r = 2 *218/(0.00476^2)

r = 19,000 km

Compared with the actual value of 6,371 km

Notes
Earth from space, image
Small angle formula

Teaching physics with Unreal Tournament

ITALICS, Oct 2006 - Volume 5 Issue 3 is on Learning With Games, Learning by Making Games

See Colin B. Price - A Crisis in Physics Education : Games to the Rescue!
They have modded Unreal Tournament to make interactive virtual worlds for:

1. Gravity and Collisions
2. Activation Energy
3. Conservation of Momentum
4. Pendulae and Newton’s Cradle
5. Oscillations: Simple Harmonic, Diatomic Molecules, Normal Modes
6. Wave propagation and Solitons
7. Potential Hills
8. Central Pattern Generators in Biological Systems
9. Waves: Propagation, Diffraction and Interference.

My humble efforts with Game Maker can be found at http://www.freewebs.com/schoolgamemaker/#lobject

Teaching physics through game programming

Pete Border has excellent resources for teaching physics through game creation.

Pete's work is excellent:
http://www.maapt.org/programs/talks/maapt_20041030_border.ppt describes the pedagogy
http://webusers.physics.umn.edu/~border/phys1905f02/ has slides, Excel sheets, Python and Blender source.

This tertiary course has been adapted for a secondary school summer camp :
http://www.umcrookston.edu/camps/documents/pdf/cybercamp_brochure2006_web.pdf