Summer 2009 Questions and Resources

Alfredo sends this link to a movie of a railroad tank car imploding.


The square of electricity

Force, Field,Potential Energy, Potential


The beinners guide ot aerodynamics, A great online book from NASA,

Bob Miller's Light Walk

Here are some light activities

Peel a CD, cut the aluminizing off a compact disk to make a transmssion diffraction grating.

Color Diffraction Grating

Image on a Mirror

Fresnel lens and Laser

Scan a Laser through a lens

Laser CD, reflect a laser off a CD to measure the line spacing of the

Laser Light, Explore the properties of laser light.

Laser Milk, Laser light scattered through milk produces a 3-d time varying interference pattern

Light Box, build a simple box to explore image making

Poisson Spot, make one with a pointer laser and a BB

Ray Tracing, How to do it

Audacity is a free sound recording program with spectrum analysis and automatic musical note identification.

Here are the notes from an Audacity workshop.

San Francisco 1906 earthquake movie

Seeing Yellow (Disagreeing about color) the Snack pdf format an article by Gorazd Planinsic.

The spectra of the elements

Paper Tape Timer reference, mathematics:

Air resistance force calculation. Why is air friction proportional to v^2 for turbulent airflow.

Information about human senses:

Howard Hughes Medical Institute, Seeing Hearing and Smelling the world.

A great source of physics information

Hyper Physics

A new source of physics data.  Wolfram Alpha

and for the thermal expansion

Perception Videos

Men carrying a door between two people videos:



Find the Highest Note

Laser Speckle explanation


We purchase our colored filters from Holtz-Muller theater supply in San Francisco, #415-826-8383

They are $6.50 per sheet, 20 x 24 inches

TI uses Roscolux Medium Red #27

Roscolux #80 Primary Blue, and

Lee Filters #139 Primary Green.

Mix and Match

Add R G B to make other colors

Phosphorescent Vinyl

From educational innovations

Difraction grating

From Project Star

Air Resistance

Air resistance F = kv vs cv^2

For laminar flow the force from air resistance is proportional to the velocity.

For turbulent flow it is proportional to velocity squared.

A bicyclist travelling at velocity v in still air experiences air friction that increases as the velocity of the bicyclist squared. F = cv^2

Let's do a simpler problem first the bicyclist colldes with a beanbag of mass m. As viewed by the bicyclist the beanbag is mving towards them and has kinetic energy E = 0.5mv^2 which goes to 0 in the inelastic collision with the byciclist. So in the inelastic collision between beanbag and bicyclist the bicyclist must do work on the beanbag to bring it to rest. The work done will be 0.5mv^2. Work is force times distance. So the force of hitting one beanbag depends on the distance over which the beanbag is brought to rest. 0.5mv^2 = F d.

Now consider a beanbag every metre, d = 1m. And calculate an average force by assuming it takes the full meter to stop the beanbag.

F = E/d = 0.5 mv^2 = Fd   so F = 0.5mv^2/d


Consider air of density p moving at velocity v colliding with an object with a front surface area A.

The air comes to rest when it strikes the object. The mass of air is pV  where V is the volume of air that hits the cyclist.

So the kinetic energy, E,of the air is 0.5mv^2 = 0.5 pVv^2 now the volume of air is Ad  so we get

E = 0.5pAdv^2

and F = E/d = 0.5 pAv^2

the air resistance force is proportional to the density of the air, the area of the bicyclist and the velocity of the bicyclist squared.


Scientific Explorations with Paul Doherty

© 2009

22 June 2009