Sunday, March 27, 2011

Zoetrope (mini)


Materials:
• 4.5” dia. clear plastic round deli container, 16 oz.
• large chopstick
• straws (must big enough to fit the chopstick, we used “jumbo” straws)
• electrical tape
• 2.25” dia. foam core washer
• 10.5”x 1” paper animation strip (with frame lines every 1.25” pre drawn)  

Tools:
• scissors
• screw
• screw driver
• tape pattern template (if making multiple or working with young children )
• hot glue gun




First, locate the middle of the plastic cup and poke a hole in it with the screw, then take a Phillips head screw driver about the size of your chop stick and widen out the hole.  Next, begin applying electrical tape strips to the side of your cup, leaving gaps no more than a few mm wide.  Note that given the cups are conical when the tape is placed straight up and down the slots should be triangular not perfectly parallel. Once you've made one good one you can save it as a template or use a sharpie to make a separate template. Templates are especially useful for younger kids as they often have trouble keeping the gaps even and straight.




Next, stick the dull side of your chopstick into the hole in the bottom of the plastic cup. Add the foam core washer (we made ours with a hole saw, but a square of about the same size will work just as well).   Make sure the chopstick is straight and add a generous amount of hot glue to the bottom of the washer and the base of the chopstick and press the washer down. 





 Cut a straw to 2/3 the length of the chop stick and slide it on. Add an electrical tape flag at the bottom of the stick to prevent the straw from sliding off. The straw will act as a bushing allowing you to hold the Zoetrope while letting it spin freely.




To use the Zoetrope draw a progressively changing image in each frame of your animation strip, place it in the bottom of the cup and hold the straw and slowly spin the chopstick while looking though the slots.

Things to do and notice: 



A Zoetrope is basically a drum shaped Stroboscope with a moving subject for observation (the animation strip) built in.  Given the slots and the animation strips are rotating at the same speed, each frame will appear in approximately the same position as the last, this makes the frame boundaries appear stationary, avoiding blurring.  At the same time the actual shapes of the drawings will appear to be changing, as each differing frame is superimposed over the last and persistence of vision blends them smoothly together, just as one would see in a flipbook. One advantage of a Zoetrope over a flip book is that it works just as well in three dimensions as in two.  The paper strip can be substituted with a series of wire or clay sculptures (or any other material) placed on a mat board disk in the bottom of the cup and a similar animation effect can be achieved. For younger students who may have trouble taping the cups a Phenakistoscope a simpler animation device that uses the same principles of operation as a Zoetrope may be a more appropriate project.  You can find many Phenakistoscope templates by simply Googling it.  The Zoetrope and similar early animation devices like the Phenakistoscope, are the technological ancestor of film and all modern forms of video media, all which employ persistence of vision blend strobbed images to the same effect of these original devices.  




Designed by Antonio Papania-Davis 2010

Sunday, March 20, 2011

Stroboscope



Materials:
•1.5” cardboard tube (we got ours from www.uline.com : S-5816, 1.5’’x36’’ kraft mailing tubes, but aluminum foil tubes would work just as well)
• foam core
• black mat board
• straw
• chopstick (that will fit in the straw)

Tools:
• fine tooth saw
• box cutter
• hot glue gun
• large scissors
• compass, straight edge 


Cut the eyepiece (3”) and the handle (6”) out of the large cardboard tube. Cut the two slots in the top of the handle, approx. 1” long and as wide as your foam core. Next, lay out the shutter disk using a compass and straightedge, the disk should be 6.5” in diameter with a small hole in the center and should have a least one radial 2”x.25” slot.  If you are making multiple stroboscopes we’ve found it useful to make one perfect template that can be traced onto other pieces of mat board. If you make a 90 degree cross on the center of your disks, a one slot template can be used to trace disks with one, two and four slots patterns.  A one slot disk will have a typical strobe light effect and is good for looking at people but will not be very effective at making fast moving objects appear still. Two and four slot disks work well for making rapidly moving (spinning or reciprocating) objects appear still, but do not work well for slower moving objects like people. Finally, cut out a foam core eye piece holder, a 2.5’’x3’’ rectangle with a semi circle the size of your I piece tube cut out of one of the short sides.  Mark the hole for the straw in the foam core  about 1.25’’ from the edge of the eyepiece cut out and in the middle height wise. You can check that the hole is in the right place be placing the center of the shutter disk over your mark and seeing if the slot completely clears the cut out in the eyepiece holder. Again, once you’ve made one of these they can be traced as these pieces do not need to be exact. You will also need two approx. 1.5” foam core washers, these can be circular or square with a hole the size of your chopstick/ straw in the middle.






After all your major materials are prepared it’s time to begin assembly.  Hot glue the eyepiece holder to handle so that the middle of the handle is directly under the hole mark in the eye piece holder.  Next, hot glue the eyepiece in place with 2” on one side and 3” on the other side of the holder. Note that you will look into the long side of the eyepiece so which side you choose to leave long will determine if you make a right or left handed stroboscope. Finally, cut a approx. 2’’ length of straw, use a nail to punch out the straw hole and then a pencil to stretch it so your straw fits snuggly.  Put the straw in the hole so that it clears the eyepiece on the short side and does not clear the long side by a good measure as seen above.  If the straw fits tightly use a small amount of glue to stick in place (too much glue can melt the straw).  If the straw fits loosely you may want to glue on a small foam core washer to shore it up (as seen with the shutter disk washer mentioned later).    




 


Next, create the shutter disk assembly. Put your disk and a washer on your chopstick. Insert the chopstick into the straw with the disk and washer on the short side of the eyepiece, and adjust their position so that the chopstick comes out the other side of the straw but does not pass the end of the eyepiece. If the chopstick is pushed too far though the straw, past the end of the eyepiece it will come very close to your other eye when you look through the stroboscope. Given this, it makes sense to look through the scope a few times before you glue the disk in place to make sure you can use it comfortably. 



When everything is aligned, glue the washer to the disk and glue the disk and washer to the chopstick on the non-straw side to keep friction down. 






Finally, add a tape flag on the back of the chopstick to prevent the chopstick and disk from falling out and you have a finished Stroboscope. To use, point at something moving, close one eye and look through the eyepiece with the other while spinning the disk via the chopstick.  We found twisting the chopstick in front of the disk is the most effective way to get the disk spinning fast, and that trying to spin the shutter disk itself tends not to work well and will eventually break the stroboscopes.



Things to do and Notice:
In the most basic sense a stroboscope is a device that exploits persistence of vision to make moving objects appear slow or stationary. In general our retinas will continue to report light for around a 25th  to a 30th  of a second after the original light source has moved depending on brightness. In the case of the disk stroboscope this plays out in two ways, it allows your mind to see the whole field of the eyepiece not just a slot and it allows this image to persist in the time the shutter is closed. For a project that explains the first effect well, see: http://www.exploratorium.edu/snacks/persistence_of_vision/index.html 
This process also allows what happened over a short time to be perceived over a slightly longer one.  In general the more slots you have and the narrower the slots the better your scope will be at making fast moving objects appear to slow, though the image may appear dim. Conversely, if you use one wider slot, slow moving objects will appear to move in steps, they will appear brighter and will persist somewhat longer. We would suggest looking at things like people playing sports with a one slot disk and things spinning or reciprocating fairly slowly like a record player or a sewing machine.  With two or four slots faster moving things like scroll saws, drills, bike and car wheels and even fans can be made to appear to stop.          

It is possible to use this idea backwards and create a mechanical strobe light simply by shinning a strong flashlight though you stroboscope in a darkened room.  
You can also take stroboscopic photography with a digital camera capable of very slow shutter speeds and through a disk stroboscope that is capable of maintaining a very constant speed (motor driven) see:   http://makeprojects.com/Project/Stroboscope/313/1     


Note: While unlikely looking though shutter disk stroboscopes can theoretically trigger epileptic seizures, like their flash tube based counter parts (strobe lights), as such similar precautions should be taken. 

Designed by Antonio Papania-Davis 2010

Monday, March 14, 2011

Camera Projector


Materials:
• 2” telescopic cardboard tubes (we got ours at www.uline.com : S-1634 kraft telescopic tubes, for smaller numbers check out your local shipping and packaging store)
• mat board or large popsicle sticks
• 1.75’’ plastic magnifying glass (we got ours from American Science and Surplus, www.sciplus.com , # 91581 plastic magnifier, these generic 2 lens magnifiers are available from many web sites but make sure they fit your tube before you order a lot of them from another source)
• white plastic grocery bags
•acetate sheets for slides (try to get these from an art store not a office supply store as they are much cheaper, alternatively any flat clear plastic from packing or flat sided bottle can also be used.)

Tools:
•fine tooth wood or hack saw and miter box
•box cutter
•scissors
•hot glue gun
•permanent markers


Preparing the tube and matt board: use a fine-toothed saw and a miter box to cut the telescopic tube into 6’’ lengths. Make sure both inner and outer tubes are cut evenly and that the ends are square, as this will affect function.  Next cut these 6” pieces into one 3.25” section and one 2.75’ section.  These lengths work well for the American Science and Surplus lenses (which have about a 3.25” focal length), but if you use different lenses you will need to change the length of the long segment so that it is near the focal length of your lens. The difference in the length can be added or taken out short segment, as its exact length is not important.  


 Now you are ready to begin assembly. Take the short tube sections and remove the inner tube from the outer. Place a piece of plastic bag (at least 3” square) over the outer tube and then push the inner tube inside.  This should stretch the plastic over the end of the tube section and will function as a diffuser in projection mode and a screen in camera mode.



Next, take the inner long tube section, find the most squarely cut end and hot glue the magnifying glass on to the end of the tube. When the glue has set put the inner tube with the magnifying glass back in the outer tube. 


Orient the parts as seen above with the plastic bag diffuser in the middle of the assembly.


At this point you can either add a mat board “foot,” a 5”x4.125” piece with scoring in 1” from the long edges.



Alternatively, three large popsicle sticks can be used to hold the assembly together.  In either case a gap of at least 1 mm should be left between the diffuser so a slide can be inserted into the projector. 



To use the as a camera simply point the magnifying glass at a well lit area and a inverted image will appear on the diffuser.  The quality of this image will depend on how closely you match the focal length of the lens to the distance between the lens and the diffuser.  Though the lens can be slid in and out to somewhat adjust focus.


To use as a projector insert a slide (note the rounded shape) into the slot and shine a flash light into the back.  Standard projector slide can be used or slides can be made by drawing on clear plastic with permanent markers. Again the lens can be slid in and out to adjust the focus.  In a dimly lit room you can expect to get at least a 1-2’ image with a strong flashlight.



Things to do and notice:
Camera projectors are meant as a simple way to explore lenses and refraction.  Lenses can gather light and form images, given their profiles cause light to converge. However, these images are always both upside down and backwards. Having students make their own slides reinforces this effectively because slides must be drawn upside down and backwards to appear normally.  This is easily done by drawing the top of the image at the bottom of the slide (the curved part) and then flipping it so it faces backwards in the projector. Trying to project a word forward and right side up will make this clear. When projecting, Spherical Aberration can be seen. Spherical lenses bend light at different rates at their centers than at their edges, typically making it easy to focus the center of the image but nearly impossible to focus the edges.  When used as a camera Chromatic Aberration can be seen when looking at bright light sources close up. Chromatic Aberration, the fact that different frequencies of light bend at different rates in a given substance (as seen in glass prisms), will cause bright lights to be ringed by a thin line of rainbow.      
      
Note: this is a modified version of a project originally designed by Lawrence Hall of Science.

Saturday, March 12, 2011

Spectroscope



Materials:
•1.5’’ dia. cardboard tubes (we got ours from www.uline.com : S-5816, 1.5’’x36’’ kraft mailing tubes, but aluminum foil tubes would work just as well)
•Black card stock
•Diffraction grating (we got ours from www.rainbowsymphonystore.com : item #10503, 6x12’’ 1000 lines/mm $25 for ten sheets, www.sceintificsonline.com item # sku 3052116-GRP, $9 for two 6x12’’ 254000 lines/inch 
•Masking tape

Tools:
•Scissors
•Hot glue gun
•Hole punch (or punches)



Cut the large cardboard tubes down to a 5-6’’ length using a fine-toothed wood saw (faster) or a box cutter (slower but potentially more accurate).  It is not important that the tubes be cut squarely but it is important that they be cut evenly so there will be no unwanted light leaks when the cardstock ends are glued on.   

Cut two approx. 1.5x2’’ pieces of cardstock making sure that the long edges are straight, these pieces will make your slot.  Place you pieces down on a flat surface with 2 of the straight edges together leaving them a little less then a mm gap between them.  Apply glue to one end of the tube and place it on the two card pieces with the gap in the center of the tube. 




After the glue sets trim off the excess card stock to prevent it from getting ripped off in the future. 



  Cut out a circle that is bigger than the diameter of your tube, we used a big 1.75’’punch from Michael’s to speed things up though it’s not necessary. Then use a standard hole punch to make a hole as close as you can to the middle of the cardstock circle.  Place a .25x.25’’ square of diffraction grating over the hole and tape it down with masking tape. 




Next, align the slot to the diffraction grating by pointing the slot end (oriented vertically) of the spectroscope tube at a light source and place the cardstock circle with diffraction grating on the other end and slowly rotate it.  Look through the diffraction grating at the side of the tube (not out the end), when the diffraction grating is aligned properly bands of colors should appear parallel to the slot off to the right or left, not a single line above or below the slot.  This may take a little while the first time around as the colors appear further from the center of the tube than most people expect, but once you find them it becomes very intuitive. Once you’ve got the scope well aligned either glue around the edge while holding the circle in place.  Alternatively, put a tick mark on the tube and circle and then glue the tube onto the circle using the mark as a guide.



Things to do and notice:
As spectroscopes are meant to analyze light, it’s a good idea to have a number of different light sources for students to look at prepared. Incandescents provide fairly full spectrum light though it’s a bit red shifted.  LEDs can create monochromatic light or compound colors depending on if they use their chemistry or their lens to color the light. Compact fluorescents are particularly interesting to look at as they almost always have incomplete visual spectrums creating strong banding.  Colored light filter’s subtractive effect can be demonstrated as they will block most colors dissimilar from their appearance. Sun light (full spectrum light) can be analyzed simply looking at a brightly lit area outside, though you should never look directly at the sun as the spectroscope does not provide adequate protection for this to be safe.  In all cases, the component colors can be related to the chemistry of the elements being excited and producing light.    Fluorescents use a combination of mercury vapor and a phosphorus coating to make various varieties of white light. LEDs use various combinations of semi conductors metals to produce a wide selection of colors, and unlikely things like pickles can even be made to glow a characteristic yellow orange when electricity is passed through them due to their sodium content.  The glowing pickle color is similar to streetlights as they are sodium vapor lamps.    


Light, Color and Perception Series


In general we are aiming to achieve four basic goals in out projects and activities:
•Presenting basic scientific concepts in an interactive manner using everyday materials
•Encouraging experimentation as a means of confirming scientific principles 
•Developing creative problem solving skills and critical thinking
•Promoting observation to reveal unseen aspects of everyday phenomena

We introduce most topics, such as light, sound, electricity in series over a few weeks in order to develop and reinforce basic concepts, and to ensure there is a balance between guided instruction and experimentation.  In the case of light we usually do a day of interactive demonstrations covering light and color, bending and reflecting light and some aspects of visual perception. Then to reiterate we make spectroscopes for color, camera-projectors for light bending/image formation, then stroboscopes and zoetropes for perception over the following weeks.  After that, depending on the age of the group a few more advanced projects can be added.  The following posts are instructions for our main four light projects.    





Friday, March 11, 2011

About:

Welcome to the Discovery Center Blog. This Blog is meant to catalogue our various projects, activities, and ideas so that they may be used and improved by students, educators and organizations.
We are currently gathering content and will be posting previous and upcoming projects and activities in the coming days and weeks . Questions and comments are welcome and encouraged, please stay tuned.