Stroboscope: Difference between revisions

From Science Theatre
Jump to navigation Jump to search
← Older editNewer edit →
imported>Stwikiadmin
VisualWikitext
imported>Stwikiadmin
Created page with "== Age == Elementary School, Middle School, High School == Format == Stage Show == Materials == Stroboscope Standard AC outlet Stroboscope "disks" Standard-h..."
imported>Stwikiadmin
No edit summary
Line 1: Line 1:
== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]], [[Biology]]:
| Light, Colors, The Eye
|-
| Grade Range:
| [[Elementary School]], [[Middle School]], [[High School]]
|-
| Format:
| [[Stage]]
|}


Elementary School, Middle School, High School
The Stroboscope demonstration uses a spinning wheel and a strobe light to introduce some interesting properties of the eye: Temporal Aliasing and Strobic Aliasing. It is also used to show the difference between Color Addition (how the colors of light mix) and Color Subtraction (how paints and dye mix).
 
== Format ==
 
Stage Show


== Materials ==
== Materials ==


    Stroboscope
* Stroboscope Motor
    Standard AC outlet
* Stroboscope discs
    Stroboscope "disks"
* Flathead screwdriver  
    Standard-head screwdriver  


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. The flashing strobe may encourage epileptic seizures - make sure the audience is aware of this before you present the demonstration so they may excuse themselves if necessary.
This demonstration uses a strobe light, so ensure that nobody in the audience nor any of the presenters suffer from epilepsy prior to presenting. Read the Physical Demonstration section of the [[Demonstration Safety]] Page before performing this demonstration.
 
==Preparation ==


Make sure that the stroboscope is plugged in and that the disk is securely locked on.


== Demonstration ==
== Demonstration ==


Demonstrate the disk to the audience.
''*NOTE*: Ask the contact or the audience before presenting this demonstration if anyone in attendance is prone to epileptic seizures. If so, they should leave the room before this demonstration, and have a co-presenter go with them to talk about the demonstration using the [[Temporal Tops]] demo.''
 
Turn on the motor without the strobe to illustrate the blurring effect.
 
Turn on the strobe. You may wish to turn off overhead lights.
 
Adjust the speed so that they are synchronized.
 
Demonstrate other disks.
 
== What to Say ==
 
Before we begin, I'd like to ask whether anybody here suffers from epilepsy. This experiment does contain a flashing lights, which can be a problem for some people.
 
Here's the disk that we will be demonstrating. You can see now what it actually looks like.
 
[Turn on the motor] With the disk spinning, our eyes blur the image together making it look like something else.
 
[Turn on strobe] With the strobe light on, we only see the disk for brief flashes. This causes it to appear still differently.
 
[Adjust the strobe speed] By adjusting the frequency of the flashes, we can change the image, making the disk appear to stop.
 
[Repeat the demonstration for multiple disks]
 
We are only viewing the disk at discrete moments in time. This is called temporal aliasing. Your mind is tricked into believing that these images all flow together, even though the disk is spinning between flashes.
 
Can anyone think of an example of this effect elsewhere in life? (motion pictures; spinning car tire appearing to move backwards)


This also illustrates the importance of choosing good samples in an experiment. If you were to live in a cave and come out only once a day at noon, you would be convinced that the sun never sets.
Preparation: loosen the screws holding the brass washer/mount, and remove it from the front of the stroboscope. remove the front aluminum disc. Place your desired stroboscope disc on the rear aluminum disc, and return the front disc to hold it in place. Slide the brass washer/mount back on, and push it tightly against the other discs as you tighten the screws into place. Plug in the strobe light to the back of the stroboscope.
# Point to the disc and ask the audience to identify the image you are using (Gears, Beach Ball, Dots, Spiral, Pistons, Red/Green/Blue Boxes)
# Spin the disc with your hand, and explain how our eyes have a "speed limit", or a limit to the number of images, or ''frames'', we can see per second (about 60 fps)
# Turn on the stroboscope, and point out the blur we now see instead of an image
# Hold the strobe light and turn it on, keeping it at a low flash rate. Slowly adjust the flash rate until you get a still image on the wheel. Explain how the strobe light is "setting the speed limit" for our eyes, giving us a certain number of frames per second.
# Adjust the flash rate until you have a dynamic image; Picture discs are "moving" or the color wheel starts blending colors. Ask for answers on why the images are moving.
# Adjust to a high flash rate, so you have a rapid dynamic image; picture discs are blurring, color wheel has a variety of colors on it. Explain the effect they are seeing.
# Turn the strobe light down to the lowest flash rate, then turn it off. Turn off the stroboscope. As it slows down, and if time permits, you can pick out a second wheel to show them!


If you come out once every 23 hours, you may even believe that the sun moves backwards very slowly. During and experiment, scientists need to take samples frequently enough to understand what is actually occurring.
==Why This Works==


[Thank the audience and ask for questions]
===Short Explanation===


== Why It Is ==
This demonstration is focusing on the effect known as '''''Temporal Aliasing'''''. Temporal Aliasing is when an object is moving quickly, or an image is changing rapidly, and the motion being too fast for our eyes to follow. Our brains then receive the blurred image, and tries to process it as a non-blurry image. The result is that we "see" a pattern or motion that isn't actually there. This effect, when used on images, is how we developed movies and videos! a video camera will take a bunch of pictures every second (usually between 30 and 40 fps), and by flashing the images at our eyes really quickly, we "see" the movement in the video happen! Animated shows, such as cartoons, usually use a fewer number of images per second, so with an animated show we can actually see the tiny "jumps" in-between the pictures.


We are only viewing the disk at discrete moments in time. This is called temporal aliasing. Your mind is tricked into believeing that these images all flow together, even though the disk is spinning between flashes.
For the Color Wheel, we are using this effect to see how the colors of light mix together. The wheel has only four colors on it: Red, Green, Blue, and a little bit of White. When it is spinning really fast, and we don't have the strobe light on, we only see a purple-pink blur. This is because the colors are blurring past each other as we look at it, so our brains, rather than try to separate each color, will blend them together. When we flash the light at a medium speed, we see the colors start to blend, giving us Cyan (Blue-Green), Magenta (Red-Blue) and Yellow (Red-Green). When the light is flashing really fast, we start to see other colors as well, but especially more white! This is because colors of light are ''additive'', meaning they give more colors as they blend. Paints and dyes, however, are ''subtractive'', meaning they absorb more colors as they blend. White light gives out all colors, and black paint absorbs all colors. White paint reflects all colors, and black light would just be no light at all. The "black lights" we use are actually violet!


== Real Life Examples ==
===Full Explanation===
'''''COMING SOON'''''


Motion pictures.
==Tips and Tricks==


A spinning car tire appearing to move backwards.
* This demonstration is a part of the [[Electromagnetism Show]].
* Be aware that some students may feel nauseated after watching this demonstration. This demonstration can trigger symptoms of motion sickness.
* This demonstration pairs well with the [[Temporal Tops]], the [[Light Box]], and could be a useful addition to a show on the senses.

Revision as of 16:15, 1 March 2016

Physics, Biology: Light, Colors, The Eye
Grade Range: Elementary School, Middle School, High School
Format: Stage

The Stroboscope demonstration uses a spinning wheel and a strobe light to introduce some interesting properties of the eye: Temporal Aliasing and Strobic Aliasing. It is also used to show the difference between Color Addition (how the colors of light mix) and Color Subtraction (how paints and dye mix).

Materials

  • Stroboscope Motor
  • Stroboscope discs
  • Flathead screwdriver

Safety Precautions

This demonstration uses a strobe light, so ensure that nobody in the audience nor any of the presenters suffer from epilepsy prior to presenting. Read the Physical Demonstration section of the Demonstration Safety Page before performing this demonstration.


Demonstration

*NOTE*: Ask the contact or the audience before presenting this demonstration if anyone in attendance is prone to epileptic seizures. If so, they should leave the room before this demonstration, and have a co-presenter go with them to talk about the demonstration using the Temporal Tops demo.

Preparation: loosen the screws holding the brass washer/mount, and remove it from the front of the stroboscope. remove the front aluminum disc. Place your desired stroboscope disc on the rear aluminum disc, and return the front disc to hold it in place. Slide the brass washer/mount back on, and push it tightly against the other discs as you tighten the screws into place. Plug in the strobe light to the back of the stroboscope.

  1. Point to the disc and ask the audience to identify the image you are using (Gears, Beach Ball, Dots, Spiral, Pistons, Red/Green/Blue Boxes)
  2. Spin the disc with your hand, and explain how our eyes have a "speed limit", or a limit to the number of images, or frames, we can see per second (about 60 fps)
  3. Turn on the stroboscope, and point out the blur we now see instead of an image
  4. Hold the strobe light and turn it on, keeping it at a low flash rate. Slowly adjust the flash rate until you get a still image on the wheel. Explain how the strobe light is "setting the speed limit" for our eyes, giving us a certain number of frames per second.
  5. Adjust the flash rate until you have a dynamic image; Picture discs are "moving" or the color wheel starts blending colors. Ask for answers on why the images are moving.
  6. Adjust to a high flash rate, so you have a rapid dynamic image; picture discs are blurring, color wheel has a variety of colors on it. Explain the effect they are seeing.
  7. Turn the strobe light down to the lowest flash rate, then turn it off. Turn off the stroboscope. As it slows down, and if time permits, you can pick out a second wheel to show them!

Why This Works

Short Explanation

This demonstration is focusing on the effect known as Temporal Aliasing. Temporal Aliasing is when an object is moving quickly, or an image is changing rapidly, and the motion being too fast for our eyes to follow. Our brains then receive the blurred image, and tries to process it as a non-blurry image. The result is that we "see" a pattern or motion that isn't actually there. This effect, when used on images, is how we developed movies and videos! a video camera will take a bunch of pictures every second (usually between 30 and 40 fps), and by flashing the images at our eyes really quickly, we "see" the movement in the video happen! Animated shows, such as cartoons, usually use a fewer number of images per second, so with an animated show we can actually see the tiny "jumps" in-between the pictures.

For the Color Wheel, we are using this effect to see how the colors of light mix together. The wheel has only four colors on it: Red, Green, Blue, and a little bit of White. When it is spinning really fast, and we don't have the strobe light on, we only see a purple-pink blur. This is because the colors are blurring past each other as we look at it, so our brains, rather than try to separate each color, will blend them together. When we flash the light at a medium speed, we see the colors start to blend, giving us Cyan (Blue-Green), Magenta (Red-Blue) and Yellow (Red-Green). When the light is flashing really fast, we start to see other colors as well, but especially more white! This is because colors of light are additive, meaning they give more colors as they blend. Paints and dyes, however, are subtractive, meaning they absorb more colors as they blend. White light gives out all colors, and black paint absorbs all colors. White paint reflects all colors, and black light would just be no light at all. The "black lights" we use are actually violet!

Full Explanation

COMING SOON

Tips and Tricks

  • This demonstration is a part of the Electromagnetism Show.
  • Be aware that some students may feel nauseated after watching this demonstration. This demonstration can trigger symptoms of motion sickness.
  • This demonstration pairs well with the Temporal Tops, the Light Box, and could be a useful addition to a show on the senses.
Retrieved from "https://sciencetheatre.kaedon.net/mediawiki/index.php?title=Stroboscope&oldid=540"