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SF Physics 26 – Solar Bag

IMG_5934This was the last class for this year so we headed to the park with the All About Air Classroom Kit from Steve Spangler Science.  I had used the windbags in the high school class to demonstrate Bernouille’s principle – you can inflate a 2 meter long bag with one breath by taking advantage of this principle.  We started out with the windbags and I asked the students to put three big breaths in the windbags and then estimate how many breaths it would take to fill them.  Then I demonstrated how to do it with just one breath, hold the opening of the bag wide open about 10 inches from your mouth and blow a steady stream of air into the bag.  Increasing the speed of the air around the mouth of the bag lowers the pressure causing the air around the mouth of the bag to rush into the lower pressure area filling the bag!  IMG_5938

The solar bag is basically a black garbage bag that is 15 meters (50 ft) long!  We took it to the middle of the park and filled it with air, using the wind instead of blowing and then tied off both ends.   As the bag is warmed by the sun, the air inside will move at faster and faster speeds causing the bag to expand, giving the air a greater volume and therefore a smaller density than the surrounding air and the bag will float!DSCF9084.jpg

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This kit worked pretty well.  My only complaint is that the string provided in the kit to tether the solar bag (required!) is really cheap thin cotton string and it snapped on us a couple of times.  Luckily, we tethered both ends so we did not lose the bag.  If I had noticed the quality of the string before arriving at the park I would have used my own.  We did end up with a small hole in the solar bag at one point, but I always have duct tape in my backpack and quickly patched up the hole.  You have to do this in the morning when its still cool and it has to be a sunny day of course.  We had trouble getting the bag to go very high by 11 am because it was already getting too warm outside.  I also don’t think we put quite enough air inside the bag before closing it, but that kind of kept it more manageable.

 

 

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SF Physics 24 – Light Technology

Today we covered the last chapter in Science Fusion Module J, Light Technology.  We started class by watching the following videos:

I didn’t show this last video by Physics Girl in class, but its got a nice demo to show how fiber optics work just using a plastic bottle, water and a laser pointer.  I had some actual fiber optics so I used those in class but if we had had extra time I would have pulled out a bottle to do this demo.

Students used snap circuits to build some circuits using  LEDs and fiber optics.  I also had out our fluorescent rock collection and short ultraviolet (UV) light to show how the incident UV light causes the electrons in the minerals to become excited and when they relax they emit visible light.

I also had a HeNe laser and LED light blox out and talked about how the laser light was different – collimated beam, the light is polarized (all wiggling in the same direction) and its coherent (all the wiggles are lined up or in-phase with each other and make interference patterns).

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Lastly, my son has night vision goggles  and I let the students explore with them a bit.  The goggles we have use active illumination and emit infrared (IR) light which you can ‘see’ using your smartphone camera.  In the photo below left, the night vision goggles are off and this is what it looks like when they are on as well. But if you look at little bulbs on the side when the goggles are on using the camera on your phone you see they look violet (photo below right).  The camera sensor is more sensitive to IR than our eyes so its able to pick it up.

Since we finished the books and still have a few weeks left in the semester I think we’re going to do a bit of astronomy to finish up the year.

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SF Physics 23 – Optics

For this class I went over how the human eye works, including color vision and then I had the students use the Light Blox to see what different lens shapes do to incoming light.  They traced the lens on their paper and then placed the Light Blox on one of the lines on their paper and traced it, with the help of a ruler, on both sides of the lens.  You can use a laser pointer for this but its not as easy to see the beam as the Light Blox. They did this for both converging and diverging lenses and a couple of them also did it for a right angle prism.IMG_5426

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Students also made an image of a bright window with a small concave lens and moved a piece paper around until they found the focal length of the lens – where the image was in focus (sorry my photo is NOT in focus). We talked about how this was a real image since you could project it on to a piece of paper.

One of the students was trying to see the image from a diverging lens (skinny in the middle) and another student noticed it made his eye look smaller and closer together (photo below).  IMG_5425

Lastly they took prisms (these are part of the lens/prism kit linked to above) outside to see the spectrum of sun light, i.e. make rainbows.

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SF Physics 22 – More mirrors

I decided to spend another day on mirrors and had the students look at images in flat mirrors and do some ray tracing with real mirrors.  I’ve already described this lab in detail a few years ago so I’m just going to link to that post, Physics 026 – Ray Optics.  I also had students look at concave mirrors and use them to project a real image on a sheet of to find the focal length of the mirror – also described in post mentioned above.

At the end of class we watched  Physics Girl explain why mirror flip images horizontally:

And we watched Crash Course Astronomy on telescopes.

SF Physics 21 – Mirrors

We started class by watching Doc Schuster’s video on Geometric Optics Intuition.

I have a set of 6 mirrors (convex and concave) that students used in Science Fusion lab Spoon Images (in the online resources).  As the title suggests you can use spoons for this lab since the spoon can be used as concave mirror (looking into the ‘bowl’) or a convex mirror (looking at the ‘bottom’ of the spoon).   I also stepped the students through ray tracing for a concave mirror with the image at various locations and we discussed whether the images were virtual or real, upside down or rightside up and whether or not the image size was different than the object size.    If you can project the image onto a piece of paper then the image is real, but if you can’t project it, like your image in a flat mirror, then its a virtual image – it just appears to be behind the mirrors but there is no light going behind the mirror.

IMG_5230We finished early and there were only 4 students today so I let them play Jishaku which uses very strong magnets and Laser Battle, which involves strategically placing mirrors to reflect light on to your enemie’s tower.  Laser Battle is very similar to one of the Science Fusion labs where students make a maze in a cardboard box and then have to use mirrors to bounce light (bright flashlight or laser pointer) through the maze.

 

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