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homeschoolsciencegeek

March 2016

Last week we had a special guest to our Big History Class, a Native American Storyteller that I happened to meet at an archery range a few years ago.  He has come to my class before and we’ve had him tell stories at our 4-H Community Club meetings. For our class last week he told stories about how the earth came to be and why certain animals look like they do.  He also told the students that storytellers were important because way back when they didn’t have a written language so the way information was passed on, was by telling stories.  Most (all?) of his stories involve fur people and he gets the kids involved in the stories by acting them out with his collection of animal hides (I believe all the hides are from road kill, and other animals that passed away naturally).

At the end he asked the kids to tell him stories and I think they enjoyed that just as much as listening to his stories.

I started class this week with a quick slideshow on refraction of light and explaining the mystery of the headless polar bears. (photo from http://teamevergreen.weebly.com/light-and-shadow.html)  Refraction, the bending of light at an interface occurs because the speed at which light travels depends on the medium its traveling through.  If light passes from air into glass, the speed of light slows down and the light ray bends closer to the normal (angle of refraction < angle of incidence), but if light is traveling in glass and then enters air, it speeds up and bends away from the normal (angle of refraction > angle of incidence).  For the polar bear in the photo, the light bouncing off its head is passing from air into some very thick windows and then back to air before reaching our eyes.  The light coming from the body of the polar bear is traveling through water and then the thick windows before reaching the air and our eyes.  The index of refraction of water is a closer to that of the window then to air, so there is a bigger shift when the light rays goes from Air/window/Air then there is for Water/window/Air, so the head and body don’t match up!

. We practiced ray tracing through thin lens, which is very similar to the ray tracing for mirrors that we did last week and actually part of the same set of handouts.

This handout has a nice discussion of the thin-lens equation and has the basically the same lab that we did in class – take a converging lens and find its focal length by using an object very far away (a bright window), then the image distance will be approximately equal to the focal length.  Then the students put a light source (bright LED) at different distances from the lens and found the image distance and magnification of the image.

I also showed this video in class, which shows how mirrors and lens focus light.

The equipment we used today included two meter sticks being used as optical benchs. The equipment can be purchased from hometrainingtools.com.  This set up works pretty well for most of these basic optics experiments.  I also recently bought this optical bench, but it was kind of frustrating to use, it was hard to tighten the screws enough to hold things steady – bad system.  So I wouldn’t recommend it.

Today we went over culture and what makes a civilization.  I gave them 2 handouts before the slideshow, one a graphical organizer where they wrote the word culture in the center and then filled the circles around it with things that define a culture.  I said, “What if I dropped you off in another country and didn’t tell you where you were.  How would you know where you were? What clues could you use?”  Some kids immediately responded with language, clothing and one said the effiel tower which led them to put down architecture or buildings.  I gave them some time to fill that out and then they had a matching worksheet where they had to match the word to its definition.  These words were all things that define a civilization: government, economy, urbanization, specialization, etc.  This was a bit tougher, especially for the younger kids (9 years old), so after they worked on a bit I went ahead and did a slideshow presentation where I talked about all the words on the sheet.  I used examples from Egypt, Mesoamerica and Mesopotamia for each subject.

I used a freebie from TeacherspayTeachers.com,  What is a Civilization? by Kelly Grant Horrocks as the basis for my slideshow and that is where I got the worksheets.

I had the kids do one more activity (labeling a world map) because I noticed in a previous class that many of these students could not identify the continents on a world map and this kind of blew my mind.  I grew up with National Geographic maps glued to our bathroom wall and when my kids did Story of the World when they were younger we didn’t do all the map activities, but I made sure they could label continents.  When ever we talk about a particular country we locate it on a map or the globe first.  Another activity we did when the kids were elementary age was put a sticker on a world map for items we bought,  bananas from Ecuador , go put the sticker on the map, apples from Washington State, sticker on the map, cotton shirt from Egypt, put a sticker on the map.  The kids loved doing this and I think its a great way to make geography a little more interesting.

We’l be playing with optics for the next couple of weeks which is always a lot of fun.  The first lab involved using a flat mirror and a pin stuck in clay as our object. The students then put their eye near the edge of the paper (at the bottom of the photo) and used a ruler to draw the reflected ray from the image in the mirror (Ar, Br, Cr) and they did that for 3 different positions of their head.  They then removed the mirror and used a ruler to continue the lines behind the mirror. These lines are draw as dashed lines because they are virtual rays, the light does NOT really pass behind the mirror, our brain just processes the reflected rays as coming from behind the mirror.  The students also drew lines (Ai, Bi, Ci) from the object to the points on the mirror that the reflected rays crossed, these are the incident rays of light.  Incident and reflected angles were measured for ray and found to be nearly identical with our error.

We also did experiments with concave and convex mirrors. Students placed a concave mirror so that it produced an image of an object that was very far away so that the incoming light rays would enter the mirror ~parallel.  We used the back door and got a fairly bright image on a piece of paper as shown in the photo below.  You can also see that the image is upside down (inverted) and smaller than the object.  Because the image can be projected on paper its called a  REAL image, the light rays actually pass through that spot and hence light up the paper.  Virtual images like in the flat mirror can NOT be projected on paper.  Once the image on the paper was in focus, done by moving the paper closer or further away from the mirror, the students measured the distance between the mirror and the paper and recorded that as the focal length.

The lab handout asked the students to draw ray diagrams in their lab books for each mirror and for different positions of the object, very far away, very close (object distance smaller than the focal length of the mirror) and with the object just outside the focal length.  Here’s what a ray diagram looks like for the case above, when the object is very far away.

At the beginning of class we went over the ray tracing rules and did some practice sheets.  Basically, the big arrow on the left is the object and you draw a line parallel to the optic axis (the big line going across the page and thru the center of the mirror), when it reflects from the mirror it must go through the focal length, F.   Likewise, a ray coming from the object that goes through F reflects off the mirror and is parallel to the optic axis.  Where those 2 rays cross is the location of the image.  Just like in the photograph of the real set up above, we see the ray diagram shows an inverted, smaller real image.

The mirrors I used for this lab were a set of 6 mirrors with different focal lengths. I believe they are the same as this set at HomeScienceTools.  If you don’t have a set of mirrors you can play around with a spoon – when you look at the part of the spoon you place food on, you’re looking at a concave mirror and you can see how the image changes as you move it farther away from your face.  The other side of the spoon is a convex mirror.

The lab handout can be found by googling “AP physics mirror lab”, the first link is the lab I used and when you click on it the document will download. I tried putting a link here but its not working.

Today we talked about why keeping track of the seasons would be important to hunter-gatherers (need to know when plants will be ready to harvest and when animals will be migrating) and the different ways people have kept track of time.  We talked about the ‘calendar’ recently discovered in Scotland that is thought to be 10,000 year old!  Holes were found in the ground that marked the position of the moon throughout the year.  In Peru, they’v recently discovered the oldest known solar observatory, Chankillo,  in the Americas (photo on the left taken on June Solstice).  13 towers mark the position of the setting sun from the June to December Solstice.  We also talked about sun dials, water clocks, candle clocks  and the ‘cosmic engine’ created by Su Song, a Chinese polymath around 1000AD.  One interesting thing I learned while putting the slideshow together, is the word ‘calendar’, comes from the Romans.  A Roman prient would call out each  month when it was a new month, and the 1st day of the new month was called the Kalends, from calare – meaning to call out.

We watched the following SciShow on the History of Time in class.

And then the kids made a pocket sundial and a star clock, which allows them to tell the time by observing the orientation of the big dipper in the sky. Both of these activities are from the Universe at Your Fingertips DVD.  Here’s a slightly different version of the pocket sun clock activity.  The sun clock is shown below, you hold it so the string is pointing North and the shadow falls on the time.  For daylight savings time you have to add an hour. And the big dipper star clock can be found here.

The activities only took a few minutes to put together so then I had the kids work in groups of 2 or 3 and fill out one of the Big History Project activities where they compare ancient civilizations.  Each group picked one civilization, Rome, Greece, Egypt, etc. and filled out a table, time span, where its located, what crops they grew, animals they domesticated, difficulties they had (dry land, volcanoes, etc) and what they’re famous for. Once they had their table filled out, they swapped information with another group so they would have information on two different civilizations.  This is a nice lead in to the Museum exhibit project they’re going to complete this month.  Again working in groups or by themselves, they’l research one civilization and give a presentation to the class at the end of the month. They can either do as the Big History Project activity recommends and build a mini museum exhibit or do a slideshow stressing why the civilization was ‘Great’.

Learn from Yesterday, live for today, hope for tomorrow. The important thing is not stop questioning ~Albert Einstein

graph paper diaries

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musings on life as a university professor

George Lakoff

George Lakoff has retired as Distinguished Professor of Cognitive Science and Linguistics at the University of California at Berkeley. He is now Director of the Center for the Neural Mind & Society (cnms.berkeley.edu).