Science Bus Fall 2005
Week 4 – Alex Tung
Quarter Theme: Light, color, and the eye
Week’s Lesson:
Persistence of Vision and Movies
Grades: 2-3, 4-5
Goals:
2-3rd: The eye and brain can blend changing images together, because the image stays in the mind
4-5th: Same as above.
Outline: Short Lecture. This lesson is meant to allow the kids to get creative and build some stuff, as well as see some cool demos to keep things lively. There will be some examples of the activities, and some materials for the students to make their own.
Introduction Lecture: Remind the students that we’ve been talking a lot about vision and light. Do you like movies? Have you seen the projector reels for movies? What do the film strips look like? Film strips are just a series of pictures that are moved quickly through a light beam to project the image on the screen. (draw a filmstrip on the white board and show how the projector shines light through the image to project it on the screen)If the pictures change quickly enough, your eye blends them together to make one motion. What about cartoons? Cartoons are done the same way, except they’re done with drawings.They take a bunch of drawings of something that changes just a little bit with each drawing, and then when they show them one after the other really quickly, it looks like the cartoon is moving. The reason this works is that when you see something, even just really quickly, the image stays in your vision for a moment, until the next image comes. This is called “persistence of vision”.(Don’t have to use this terminology – or if you do, try to ask if they know what persistence means).
(There’s a cool freeware program that lets you animate stick figures easily called Pivot StickFigure Animator - We’ll have this on a projector for the demo so we can show the concept on the screen.
Today we’re going to make some of our own cartoons, and look at how we can trick our eye into seeing motion when all we have is a bunch of pictures. We’ll also play around with a strobe light to see how we can make things that are moving really quickly seem like they’re slowing down.
Activity 1: Flip Books – Be your own cartoonist
Materials: Pens, Post-it note pads (split these in half)
Goal:To demonstrate how cartoons are made
There will be some simple examples if the kids want to make their own, or they can flip through the examples. What happens when you flip through very slowly? Quickly?
We’ll have a number of flip books available for the kids to make their own. Let them explore and be creative with this – the key will be to come up with a story first (a simple one), and to try and draw things the same size on each page. You can start on the bottom of a pad and roughly trace the picture underneath each successive page.
Activity 2: Thaumatropes
Materials: note cards, hole puncher, string
Goal: To demonstrate one of the earliest forms of animation
Reference -
Flip Sticks -
Info:The Thaumatrope was created in 1842 as an optical toy. It features a two-sided piece of stiff cardstock with string attached through holes on either side. There’s a picture on each side, and when you twist the strings between your fingers to spin the card, it combines the pictures together. You can use notecards and fold them in half so one side doesn’t have lines showing.
Encourage the kids to draw their own thaumatropes – there will be some examples for them to look at, and there should be plenty of materials for them to make more than one. Some ideas: bird in a cage, fish in a bowl, person in a house, etc.if you tie the strings as shown in the above pictures, you need to draw one picture upside down relative to the other, so when you turn the picture over it shows right side up. You can also create the same effect by mounting the card to a stick and twirling the stick.
You might keep the conversations going by noting this was the closest thing they had to TV or movies. What happens when you spin the cards really quickly? Slowly?
Activity 3: “Afterimage” cards
Materials: Markers, pieces of paper with two dots centered on each half, color wheel
Reference:
Reference:
When you stare at an object of a certain color for a few seconds, and then look at something white, you will see an image of the original object but in its complementary color. You can link this back to the ideas of color and light in the last lesson.
Have the students try the exercise with one of the example pages. Stare at the dot in the image on one side of the page, and then look over at the dot on the other side of the page. What color is the “after image”? Why do you think that is? Do you remember the last lesson about different colors of light and how they can add together to make new colors? Well when you stare at something of a certain color, your eye gets used to that color. When you look at something white (remember we said that white light is made up of many colors?), you see everything except that color.
Have the students draw a picture on half a sheet of paper using complementary colors to what they would normally use. So if they want a simple scene with an orange sun and green grass, have them color the sun blue, the grass red, etc.Start with something simple, like a single fish or bird or smiley face. We’ll have sheets of paper with dots already on them – the dots just serve as a focus for where to look. Then, have them stare at the dot in their picture for 30 seconds, and have them look over at the other dot on the blank side of the page. The scene should be the “normal” colors.
Activity 4: Slotted Tubes (at same station as above)
Materials: cardboard tubes (2-3 ft long), cardboard ends with slots cut into them, tape
Goal: To show how persistence of vision can allow you to use motion to view a larger image through a small opening.
Slotted tubes -
(This activity can probably be combined with another activity, rather than be its separate station. Try not to let the kids hit each other with the tubes!)
Take a tube and tape one of the ends to it. Look through the end without the slot at a picture or a busy scene.
What do you see if you hold it still? move it slowly? (you only see a small portion of the picture) If you move it quickly back and forth, what do you see? (you can see more and more of the picture quite clearly.) Why do you think this is? You can have the students experiment with moving the tubes at different speeds or using ends with different shapes cut into them.
Activity 5: Strobe Light
Materials: Strobe Light, Fan, water faucet, pen
Goal: To show how you can “take pictures” of an object that’s moving really fast and trick your eye into thinking it’s moving slowly, or that it’s moving backwards.
We have a strobe light from Kelly at the HaasCenter (Be very careful with it!). Start out by saying we’ll pretend that the strobe light is a camera and we’re going to take lots of pictures very quickly with it. There are a couple of activities you can do with it. For the older kids, you might get more into talking about how the timing of the flashes affects what “motion” you see.
-Pen – you can sweep a pen between your thumb and forefinger and try and keep it at the same rate, while changing the rate of the strobe – how many pens can you see? (if there’s a computer screen (CRT) in the class room, you can also go and sweep the pen in front of the screen – you should get a similar effect)
-Fan – turn on the fan with a dot on one of the blades – ask the kids if they can see the fan blades moving. Which direction are the blades moving? They’re moving really quickly so you can’t really see them. What if we used a strobe light to “take pictures” of the blades at certain points in time? Then you might be able to see them. If we change how quickly we flash the strobe, we can get more or less pictures of the fan in a certain amount of time. Your eye gets fooled because it gets a lot of light bounced off from the blades but only at certain times. If we get pictures of the fan every time it’s in a certain position, it might look like it’s not moving at all. You can let the kids play with the knob, but have them be careful with it. Be sure they don’t try to touch the fan or the glass in front of the strobe.
-Water faucet – turn on a water faucet so it drips quickly – if you adjust the strobe correctly you can make it seem like the drops are going upwards. If you put your hand underneath, you can make it seem like the water is coming up out of your hand and into the faucet
Activity 6: Zoetropes (Axed)
Materials: Zoetrope handouts, wooden dowels, straws
Goal: To show another method of making motion out of still images
Reference:
In this activity, the slits are the “picture takers” that allow you to see the image as it moves. This one takes a bit of construction, so we might not do it, but I thought I’d leave it in here anyway.
Activity 1: Flip Books – Be your own cartoonist!
Materials: Pens, Post-it note pads (split these in half)
Goal:To demonstrate how cartoons are made
Step 1: Think of a simple story (ball bouncing, person walking, airplane flying)
Step 2: Start at the bottom of the stack and draw your first picture
Step 3: Flip to the next page on top and using the outline of the first page as a guide, make a small change to the picture.
Step 4: Repeat Steps 2 and 3 until you’re done with your story.
Step 5: Flip through your new cartoon!
Discussion: When they make cartoons, they do it this way, with lots of people drawing lots of pictures. How long did it take to make your cartoon? How long does it last when you flip through it? Can you imagine how many drawings it would take to go through an entire movie? (24 frames per second for Disney movies – 130,000 frames in a 90 minute movie!!)
Activity 2: Before Cartoons...Thaumatropes!!!
Materials: note cards, hole puncher, string
Goal: To demonstrate one of the earliest forms of animation
Make your own:
Step 1: Think of two different pictures you’d like to combine together.
Step 2: Take a note card and draw one picture on one side.
Step 3: Draw the other picture on the other side (make sure you draw it upside down if the holes are on the sides of the card).
Step 4: Get a tutor to help you tie strings to the sides of your card
Step 5: Hold the strings and twist them between your fingers to make the images blend together.
Discussion:These were the toys people had before there was TV or movies, but they work the same way. When you spin the pictures quickly enough, the image on one side stays in your mind and when it flips over, you see both images blended together.
Activity 3: “Afterimage” cards
Materials: Markers, pieces of paper with two dots centered on each half, color wheel
Goal: To show that the eye can get “used to” certain colors when you look at the color for a long time.
Step 1: Try to stare at the dot in one of the pictures for about 30 seconds. Keep staring!
Step 2: Quickly look at the dot on the other side of the page – what do you see?
Make your own:
Step 1: Think of something you want to draw.
Step 2: Look at the color wheel and choose a color that is “complementary” to (across from) the color you would normally choose. If you want to draw something blue, use orange instead.
Discussion:What color is the “after image”? Why do you think that is? Do you remember the last lesson about different colors of light and how they can add together to make new colors? Well when you stare at something of a certain color, your eye gets used to that color. When you look at something white (remember we said that white light is made up of many colors?), you see everything except that color.
Activity 4: Slotted Tubes (same station as Afterimage cards)
Materials: cardboard tubes (2-3 ft long), cardboard ends with slots cut into them, tape
Goal: To show how persistence of vision can allow you to use motion to view a larger image through a small opening.
Step 1: Take a tube with a slotted end to it.
Step 2: Look through the end without the slot at a picture or a busy scene.
Discussion: What do you see if you hold it still? What do you see if you move it slowly back and forth? If you move it quickly back and forth, what do you see? Why do you think this is?
Activity 5: Strobe Light
Materials: Strobe Light, Fan with dot drawn on one of blades, water faucet, pen
Goal: To show how you can “take pictures” of an object that’s moving really fast and trick your eye into thinking it’s moving slowly, or that it’s moving backwards.
Fan: Turn on the fan with a dot on one of the blades. Which direction are the blades moving? Can you tell? What happens if we change the speed of the flashing – can we make the fan blade look like it’s slowing down? Stopped? Going backwards? What’s happening here?
Pen: Sweep the pen between your thumb and forefinger and try and keep it moving back and forth at the same speed, while changing the speed of the strobe flashes – how many pens can you see?
Water faucet:Turn on a water faucet so it drips quickly. What happens when you turn on the strobe light? Can you make the water look like it’s going up? What’s really going on here?