Wednesday, November 14, 2018


There are many demonstrations on how and why the sky is blue.  But this one might be the simplest.  In this video, Anna Spitz shows how to create a blue sky effect with just a glass of water and a drop of milk.  It is called Rayleigh Scattering.

The AAPT Films Video: Blue Sky in a Cup - Starring Anna Spitz.  Written and Directed by James Lincoln.

Of course, Anna Spitz has already hosted a video about the blue sky in this video from Arbor Scientific:

Check out more videos like these at

Friday, January 27, 2017

See Inside Your Own Eye and Hear Your Own Muscles


The human eye is not without its flaws.  Some of these include the blind spot, poor peripheral vision, and the fact that our retina is covered by blood vessels!  Normally, these arteries are invisible to us, but they can be made visible with only a cell phone flashlight.

In this video Anna Spitz explains how to use a flashlight to see your own retina.

The experimental set up – only a gently closed eyelid and flashlight are needed.

All human skin is partially transparent to light, especially red light, and we can use this to see through our own eyelids.  (This experiment works, no matter what skin color you have!). 

To perform the experiment, turn a flashlight on and hold it DIRECTLY UPON your gently closed eyelid.  Then wiggle the light as you look around with your eyes closed.  It seems to work best when the light is near the nose.

  A simulated image similar of what you will see on the surface of your retina.

When you succeed you will see several arteries emerging from a single location.  This is the optic nerve.  You might also notice a dark or grainy spot in the center of the retina that has very few arteries near it.  This spot is called the Fovea, the most sensitive part of your eye.

A view of the author’s retina from a recent visit to the eye doctor.  Notice there are very few arteries on the fovea, thereby not interfering with this most-sensitive part of the eye.

The optic nerve obstructs a small part of the retina from seeing.  This location is known as the blind spot.  Our brains hallucinate a patch over this blind spot so that we generally do not notice it.

The fovea is darker because it absorbs more light, being the most sensitive part of the eye.  It is also the part you use to read and see color.  Generally, light that is not landing on the fovea is quite blurry and the color vision is poor peripherally.  You can notice this by looking at the wall and trying to read what is on the computer screen.  YOU CAN’T DO IT!  Even though you know there are words, they aren’t legible.  Also, at night, your color vision is very poor so the fovea isn’t much help and your peripheral vision is just as good as your central vision. 

As a final note, everyone’s retinas are different as you will easily see by comparing these pictures, or any picture of a retina to your own.  Thus, you can use retinal scans as an alternative to finger print identification. 

If you are surprised that you have arteries in your eye and have been looking at them your whole life but haven’t noticed, then consider this test.  Are you wearing a shirt?  You didn’t notice until you were asked because you are used to it.  Similarly, we don’t notice we have arteries on our retina until a light hits them at an angle to which we are unaccustomed. 


Another experiment you can do with almost no equipment is to hear your muscles.  By simply putting your fingers in your ears.

Anna Spitz demonstrates that by putting your fingers in your ears, you can hear your own muscles.

That low frequency rumbling about 30 Hz is the twitching of the muscle fibers in your arms.  Muscle cells are fibrous bundles that grow and contract.  They are all over the body, but they only do one thing.  PULL.  Muscles pull on tendons.  They are even pulling when you think you are at rest.  They are pulling repeatedly just to hold you in place. 

A microscopic view of muscle cells.  All they ever do is pull.

Watch Anna Spitz explain how to hear your muscles in this video:

 Flexing will increase the loudness of the muscle twitching.

Many people mistakenly believe that this sound is the flowing of blood, but this is not the case.  The twitching sound is not timed with the heartbeat, and if you flex the muscle cells get louder. 
Flexing is when two or more muscle groups pull against each other.  For example, biceps and triceps can pull against each other and the arm will stay in place even through the muscle fibers are pulling and pulling.  The repeated pulling action of muscles we call twitching.  The frequency of this action must be between 20 and 40 Hz because that is the frequency we hear. 

Anna Spitz attempts to listen to other peoples’ muscles.

Check out more videos like these at

Tuesday, April 19, 2016

Physics Video Tuesday - Electric Field Demos!

Physics Video Tuesday    April 19, 2016

Visualizing the Electric Field  by James  Lincoln

For as long as I have been a Physics Teacher, I have been interested in making the Electric Field visible to my students.  This is IMPOSSIBLE because it is literally imaginary.  Despite this challenge, I have researched and demonstrated the best ways to display it.  What follows is a collection of videos I have created to demonstrate and describe the Electric Field. 
Perhaps the best way to demonstrate it is with Potassium Permanganate crystals which dissolve slowly on a damp saline cloth. 

ELECTRIC FIELD Visualized with Crystals

For AAPT Films, I created a two-part documentary on all of the best ways I know to demonstrate the electric field:

Ten Ways to SEE the Electric Field - Part 1

Ten Ways to SEE the Electric Field - Part 2

It is not enough that we simply show the effects of the electric field, but we must also know the rules of how it behaves.  Here are two videos I made for UCLA Physics on the Rules of Drawing Electric Field Lines and Rules regarding the behavior of Conductors:

5 Rules of the Electric Field

5 Rules for Conductors

In my research, I did create an original contribution to these demonstrations that I think makes a classic work much better.  In this video, I have some more of my lettuce seed demonstrations.  I have written an article about making this yourself from a coat hanger and Styrofoam cups:

Lettuce Seed Demonstrations

This demonstration is typically performed using grass seeds:

Grass Seeds Electric Field Demos

Monday, January 25, 2016

Physics Video Tuesday - January 26, 2016

AAPT’S Physics Video Tuesday     January 26, 2016

Sulfur Hexafluoride and Helum – At the Same Time! Explained        by James Lincoln

Sulfur Hexafluoride vs Girl (Anna Spitz)    by James Lincoln and Anna Spitz

These two videos we made to feature some of the demonstrations that can be done with Sulfur Hexafluoride.

The first was made by James Lincoln as part of a video contest and the second was made by James Lincoln and Anna Spitz as part of a video demonstration series.

Sulfur Hexafluoride is available from Flinn Scientific, and should only be inhaled from a balloon, as should helium, and never from the bottle directly.


Sulfur Hexafluoride with Musical Instruments by Kyle Forinash

Using Helium and SF6 in a trombone and a few other instruments.

Sulfur Hexafluoride Deep Voice Gas by Steve Spangler Science

Spangler does the voice demo, and floats a boat on it, as well as show that SF6 prevents sparks.

Related Articles from The Physics Teacher

Helium & Sulfur in Musical Instruments:

Helium Speech - Applied Standing Waves:


To submit a video or make a suggestion email James Lincoln:

Monday, January 18, 2016

Physics Video Tuesday!

AAPT’S Physics Video Tuesday     January 19, 2016

Polarization Physics: AAPT FILMS     by James Lincoln

In this video you will find about 20 physics demos using polarizers and related equipment.  
Also included are explanations and instructions on how to succeed doing them.

      1.     Crossed Polarizers
2.      The Mechanical Polarizer (analogy)
3.       The Construction and Axis of Polarizers
4.       The Triple Polarizer
5.       Light waves as vectors
6.       LCD Screens
7.       Circular Polarization
8.       Stress in Plastics, Glass, & Packaging tape
9.       Prince Rupert’s Drop
10.   Reflected Glare
11.   Glare on surfaces
12.   Polarized Sun Glasses
13.   The Polarized Sky
14.   3d Glasses
15.   Malus’ Law (Angle vs Intensity)
16.   Brewster’s Angle
17.   The Faraday Effect
18.   The Verdet Constant
19.   Microwave & Radio Polarization
20.   Projector Polarization

This video was created as part of the AAPT Films Series.  
The series is written, directed, and hosted by James Lincoln.  
This particular video was funded by the AIP Meggers Grant. 


UCLA Physics: Circular Polarization   by James Lincoln

UCLA Physics: Polarization of Light   by James Lincoln

60 Symbols

Polarization (of Microwaves too!):

Paul Hewitt

Hewitt-Drew-it Polarization:
Polarized Glasses Explained:

Related Articles from The Physics Teacher

Microwave Polarization:
Malus’ Law (using Lasers):
Model of Polarizers:
To submit a video or make a suggestion email James Lincoln:  James[at]

Friday, October 16, 2015

Happy Halloween! Glow in the Dark this Month with Willemite!!

Willemite is my favorite fluorescent rock.

In this video, I use willemite to demonstrate that there are different colors of ultraviolet light, and that quartz is transparent to UV.

Stay tuned for more information about my top minerals and elements recommended for physics experiments and demos.

Wednesday, September 9, 2015

Behind the Scenes Interview with Anna Spitz

Go behind the scenes with our host Anna Spitz and learn what it was like to film the series "Try This Experiment Right Now!"

LincolnPhysics: Which video was your favorite and why?

Anna Spitz: Sing Happy Birthday” would have to be my favorite. First off, it was extremely fun to film.

Anna Spitz: I remember taking a lot of time convincing certain members of the crew to take part in it, and even trying to get myself to sing publicly was a necessary and fun challenge. Once we all got into it, it started to come together. We ended up doing a lot of laughing in between takes, which makes it the most memorable to me.

LincolnPhysics: Which video helped you learn something new about science that you did not know/found the most interesting?

Anna Spitz: Audio Triangulation” was the most interesting to me, because it seems so simple, yet it is such uncommon knowledge. 


 Anna Spitz: Of course it takes more time for sound to travel to the further ear, but only a physicist would actually think of that. I think this video helped me in particular to start thinking like a physicist and looking for answers to questions without obvious answers in everything around me.

LincolnPhysics: Which video was the most challenging to act in and film?

Anna Spitz: This is a question that I don't need to think for even a full second about. “Up Down Dizzy” was hands down the most challenging thing I have ever filmed.


 Anna Spitz: For starters, we filmed in a pretty busy park with airplanes flying overhead and we needed clear audio for my speaking part. This meant we had to stop, what felt like every two minutes, to adjust, move, or wait for whatever sound was happening to stop so that we could film. The most challenging part of all was attempting to do this demo despite my severe lack of athleticism. We filmed dozens of clips of me spinning and falling until we could get the most graceful clip. 

This took some time as gracefulness is hard to find in doing the "Up Down Dizzy" experiment. I fell down after about three seconds in every take, and in one in particular, I fell backwards and fell directly on my head, which was the worst injury I've had in years (again, lack of athleticism).

LincolnPhysics: Which video do you think EVERYONE should watch and why? 

Anna Spitz: Probably “How to See Your Retina.” It is so easy and fun to do this one! This one is the most relevant in my opinion, because everyone's retinas are as unique as their fingerprints and retinal scans could be the way of the future.

 Anna Spitz: It's an interesting experience because the experiment is done the same way for everyone, yet there is a unique outcome for everyone, as well.

Thanks, Anna, for giving us a behind the scenes look at the making of these interesting short videos! 

Check out all of the "Try This Experiment Right Now!" videos on our YouTube Channel, AAPT Films.