Spinning Illusions Your eye and brain are just slow enough to see several things at once. Parts: Circle Spinner Thin cardboard String – strong and thick White paper Thaumatrope 1 Baseboard 1 Paint paddle 2 Popsicle sticks Cardboard, thin Rubber bands, medium White paper Phenakistascope File folder or thick paper 2” 1x2 wood 8” ¼” dowel Pushpin Patterns. Use the one at the end of this write-­‐up, or search for them on the web and print them out. Black paper Extra Tools: Stapler Big cups for circle Markers Nail, small to balance Circle Spinner and poke holes Glue stick (Not hot) Mirror Concepts: •
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Your eye has limits to how fast it can see two distinct pictures. When two colors or pictures are moving through the same area too fast, they get mixed in your eye. Movies and video screens use this concept. We are actually watching a lot of non-­‐moving images flashing quickly across the screen. Our eyes can’t distinguish the individual images fast enough so it looks like everything is moving smoothly. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. How To Build: Spinning Disk Draw one cardboard circle and two white paper circles. Sandwich the cardboard between the two white circles and glue them. Balance the finished circle on the head of a small nail. When it is balanced, press it down a bit so that the nail’s head makes a small indentation. The indentation should then be exactly in the center of the disk. Poke two holes with the nail on opposite sides of the indented circle. Cut about 5’ of string and pass one end through each hole. Tie the ends of the string together to make a loop. Decorate the circle with colors, thinking about which colors will mix together when the circle spins. Wind it up by making it swing like a jump rope between your hands. Pull your hands apart firmly then release again and again in a rhythm to get it going. Check out the mixed colors. Thaumatrope Cut a paint paddle in half. Hot glue each half to one end of the baseboard on the same side. Hot glue Popsicle sticks in triangles for braces. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Cut a piece of cardboard that will fit between the two vertical paint paddle pieces. Cut white paper pieces of the same size and glue them to the cardboard on either side. Slip a rubber band around the resulting sandwich. Move the rubber band exactly to the center and staple it. The staple may straddle the rubber band, or penetrate it as shown here. Draw one half of a picture on one side of cardboard. Flip the piece vertically and draw the other half of the picture. Do this carefully, flipping it back and forth in the same way that it will flip on its stand to be sure it will look right. Draw two halves of a picture that will fit together well roughly; it is hard to make a very precise fit. Stretch the rubber band from one paint paddle to the other. Check your pictures again. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Wind the cardboard up and let it go. If the two halves don’t fit together well, you may have to make another try at the drawing. You can make several cardboard pieces with different pictures to use on your base. Phenakistascope Glue a phenakistascope pattern onto a file folder. Glue that in turn onto a piece of black paper. Cut out the face as carefully as you can, including the little tabs between each image. You will peer through these slits to view the motion. Make a hole in the center with a pushpin. Wiggle it around a little to make the hole a bit loose so that the circle can spin easily on the pin. This pin can go into the eraser of a pencil and the toy is ready to go. It works better with a large flat surface backing it though, so cut a 2” piece of 1x2 and drill a 15/64” hole in it. Hammer a long dowel into the hole. Push the pushpin through the hole into the 1x2 on its flattest side. Hold the dowel so that the pictures are facing a mirror and the circle is free to spin. Put your eye close to the circle and spin it while looking through the slits at the image of the pictures in a mirror. You will see a short movie clip again and again. Spin it backwards to see what happens. Once you understand the phenakistascope, you can try to draw your own patterns. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Focus Questions: 1. If you made the color spinner bigger, do you think it would go faster or slower?
2. What would happen if you had three or four sides to the thaumatrope? 3. Why do you think we used such small rubber bands on the thaumatrope? 4. What would happen if we didn’t use black backing on the phenakistascope? Elaboration: TVs and movies consist of images flashed on the screen 60 to 72 times per second. In the early days of movies, the images were flashed much less often, giving a flickering effect (“Let’s go see a flick!”). The reason we can enjoy video presentations is that our eyes have a limit to how fast they can resolve and distinguish flashing images. Flashing images in a film present motion in small increments. Our eye-­‐brain system puts these images back together into realistic looking motion. In the phenakistascope, we present pictures to the eye just as in a movie. A limited number of pictures will fit on our wheel, so we get only a little bit of action before it all starts over. When the motion is something cyclic, such as a wagon wheel turning, sometimes an additional illusion will come into play. If a wagon wheel has 10 spokes, and one frame of a film is taken every time the wheel goes 1/10th of a revolution, you will perceive that the wheel is not moving at all. In each frame a new spoke has taken the place of the one from the last frame. If the film’s frames are taken slightly faster, the wheel in the film will appear to be going backward (the new spoke won’t have quite gotten to the position of the last spoke); slightly slower and the wheel will appear to be going forward. One of the most amazing demonstrations our eye’s limited speed of resolution is when the colors on the spinning disk toy mix together. Most of us have had experience mixing colors on paper, but here the colors remain separate on the paper. It is only in your eye-­‐brain system that the final color “exists” as you spin it rapidly. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. A spinning disk with a larger diameter will have more inertia. That is, it will take longer to start up and to slow down. This may be exactly what you want in a good spinner. Making it heavier also increases the inertia, and would have the same effect. In the thaumatrope we can see the two images from opposite sides of the paper at the same time, because the cardboard is rotating so fast. If you put a large rubber band on it turns faster. If it turns too fast, the drawings present themselves for too short a time and are less clear. If there were several sides instead of just two, you may be able to make a real movie, but there are several factors making it difficult. The images have to be exactly in the same spot when they come around, and there has to be a moment of relative darkness between the pictures or the eye-­‐brain system will blur them. In the two-­‐sided thaumatrope, this moment of darkness happens as the edge of the cardboard swings by. In the phenakistascope, the black space between the slits gives a large moment of darkness. Try it with white backing instead of black; it should be less clear. Links to k-­‐12 California Content Standards: Grades k-­‐8 Standard Set Investigation and Experimentation Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other strands, students should develop their own questions and perform investigations. Grades k-­‐12 Mathematical Reasoning: 1.0 Students make decisions about how to approach problems: 1.1 Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns. 1.2 Determine when and how to break a problem into simpler parts. 2.0 Students use strategies, skills, and concepts in finding solutions: 2.1 Use estimation to verify the reasonableness of calculated results. 2.2 Apply strategies and results from simpler problems to more complex problems. 2.3 Use a variety of methods, such as words, numbers, symbols, charts, graphs, tables, diagrams, and models, to explain mathematical reasoning. 2.5 Indicate the relative advantages of exact and approximate solutions to problems and give answers to a specified degree of accuracy. 3.0 Students move beyond a particular problem by generalizing to other situations: 3.1 Evaluate the reasonableness of the solution in the context of the original situation. 3.2 Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems. 3.3 Develop generalizations of the results obtained and apply them in other circumstances. © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Grade 2 Standard Set 1: Physical Sciences The motion of objects can be observed and measured. 1.c Students know the way to change how something is moving is by giving it a push or a pull. The size of the change is related to the strength, or the amount of force, of the push or pull. Grade 3 Standard Set 1. Physical Sciences (Energy & Matter)
1.c Students know machines and living things convert stored energy to motion and heat.
Grade 8 Standard Set 2. Forces: Unbalanced forces cause changes in velocity. 2.a Students know a force has both direction and magnitude. 2.e Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction). Grade 9-­‐12 Physics Standard Set 1. Motion & Forces Newton’s laws predict the motion of most objects. 1.b Students know that when forces are balanced, no acceleration occurs; thus an object continues to move at a constant speed or stays at rest (Newton’s First Law). © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. [SI-­‐030] © 2011 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included.