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December 2015

Big History 015 – Rocks!

IMG_1454This was the last class before break and the last one on Earth science.  We started class by making sedimentary, metamorphic and igneous rocks with starbursts.  The kids started with 3 starbursts of different colors and cut or ripped them into little pieces.  IMG_1457By lumping these ‘sand’ particles together and pressing lightly they had a sedimentary rock… made of sediments.  Then the students warmed up their starbust rock in their hands and pressed it between wax paper – putting all their weight on it.  Now its a metamorphic rock.
IMG_1460Finally we took one student’s ‘rock’ and placed it on a hotplate to melt it, making ‘magma’, then let it cool into an igneous rock.  You can find lots of videos of this activity on youtube.

The kids taped a picture of the rock cycle into their notebooks along with the data table for the next activity – identifying mineralsdiagram rock cycle.

I have two  mineral sets, one small one I bought to go along with Real Science Odyssey by Pandia Press many years ago and a large one with over 75 minerals.  Both kits came with streak plates and iron nails when I bought them.  The kids worked together in small groups trying to identify the minerals I gave them.  Each mineral has a small sticker on it so we can look it up at the end of class to see if they were correct.  I took the lab straight from Real Science Odyssey Earth & Space Level 1.  IMG_1461The students wrote down a description for each mineral, color, luster, whether it was magnetic or had crystals, what color streak it made on the plates and then they tested the hardness of the mineral.  You do that by comparing it to objects with know hardness, like a fingernail which is 2.2 on the Moh Hardness scale.  So if you can scratch your fingernail with the mineral than its harder than 2.2.  If your fingernail scratches the mineral then the mineral is soft and has a hardness less than 2.2.  They compared their minerals to copper (penny), iron (nail) and a steel file.  Once they had completed the data table for each mineral they compared their results to a data table to identify their mineral.  One of the families brought donuts, so once everybody had cleaned up, we feasted on donuts.

We didn’t have time in class but I asked the kids to watch these videos at home.

Physics 015 – Ideal Gas Law

This chapter was actually called Thermodynamics but in class we just played around with the Ideal Gas Law,

PV  = nkT,

or

PV  = NRT

P = Pressure, V = Volume, n = number of atoms, k is the Boltzmann’s constant, and T = Temperature.  The second formula is basically the same thing but instead of the number of atoms, N = the number of moles.  1 Mole contains 6.0×1023 atoms, so its just another way of talking about the number of atoms, like a dozen eggs, means 12 eggs, 1 mole of Hydrogen means 6.0×1023 H atoms. R is the Ideal Gas Constant.

Before we dug into the ideal gas law, we discussed pressure and its definition as Force per unit Area. I gave the example of stepping on someone’s toes wearing my sneakers… not too bad since my weight is spread out over the bottom of my sneaker, but, what if I was wearing spike heels and stepped on your toe with the heel?! All the students winced in imagined pain, knowing intuitively that that would be more painful. The same force applied over a tiny area has a greater pressure than if applied over a large area. We also talked about how pressure in a fluid (liquid or gas) only depends on the density of the fluid and the height of the fluid above you. The deeper you go in the ocean, the more pressure your body will experience from all water above you. Same for us standing on dry land, but under an ocean of air. As we go up in our atmosphere there is less air above us and the pressure decreases. Animals that live in the deepest part of the ocean are under extremely high pressure but their bodies are built to withstand those pressures, but if they are brought up to the surface their bodies explode because of the high pressure inside their body and sudden low pressure outside (when at the surface). Our bodies have trouble adjusting to changes in pressure as well. Divers have to be careful not to get decompression sickness or the bends – which happens when nitrogen dissolved in their blood forms bubbles when they return to the surface too quickly. This can have terrible effects on the body, including the brain.

09518686I did a few demonstrations in this class, including letting the students try to pull apart the miniature Magdeburg hemisphere that I had.  The story with this goes that the original Magdeburg hemispheres were made to demonstrate the air pump (vacuum pump) that Otto von Guericke had created.  They pumped out the air and 30 horses couldn’t pull them apart!  The air pressure outside the spheres was so much greater than the low pressure inside they could not be pulled apart.  These smaller ones are just pushed together like suction cups to force out the air, so the pressure difference is not huge, but its enough that only the strongest students could pull them apart.

We also crushed a few soda cans with air pressure.  You take an empty soda can, put a little bit of water in the bottom, maybe a cm deep.  Put it on a hotplate or your stove and heat it until you see steam escaping from the top of the can.  Then grab the can with tongs and quickly turn it upside into a pot of very cold ice water.   The can will almost instantly collapse as the water vapor inside the can condenses leaving very little ‘air’ inside the can so the outside pressure can easily crush the can.  You can see this demo and learn a lot about the ideal gas law by watching this Crash Course  video from their Chemistry series.

You can also find a lot of videos on youtube where they crush slightly bigger cans.

I also had the students put little marshmallows in large syringes which we could cap.  By pulling back on the syringe you increase the volume (V) of the gas, since T is constant, P must decrease (see ideal gas law above).  When the pressure decreases the marshmallow expands and when you increase the pressure by pushing the syringe in (decreasing V), the marshmallow shrinks.  This works because the marshmallow is filled with little pockets of air.  We put a few in the microwave and watched the volume increase as the temperature increased (P was constant)… yet another example of the ideal gas law.  Here’s a youtube video demonstrating the marshmallows in the syringe.

The main experiment involved Boyle’s law, which is still the ideal gas law, but with T constant you end up with PV = constant.  IMG_1441 I used a Boyle’s Law apparatus which is just a syringe embedded in wooden blocks so its easy to stack books on the syringe to increase the pressure on the volume of gas trapped in the syringe.  The students started with a volume of 30mL, put the cap on the syringe (hidden by the bottom wooden block in the photo), then continued to measure the volume of the trapped air as they placed more and more books on the syringe.  They recorded the applied mass, calculated the Force and Pressure on the gas, added atmospheric pressure (the pressure exerted by the air around us) and they recorded the new volume.  At the end they multiplied the calculated P (from their applied mass) by the Volume and found it was indeed constant.  We ran out of time in class but they should be making a graph of V vs P to put their lab book.

 

Big History 014 – Earthquakes

While we watching movies about the layers of the earth last week, I heard one of the students ask, “How do we know that?” Which is a great question because we haven’t dug down to the center of the earth, heck, we haven’t even gotten through the crust yet. So how do we know there is an iron core in the center of the earth surrounded by a molten outer core?  Earthquakes!  Earthquakes generate waves that travel through the earth and we can measure them with seismographs.seismogram  Just like we use radar or sonar to detect things we can not see, we can use waves from earthquakes to learn about the center of the earth.   There are two main types of body waves (waves that travel through the body of the earth), P – waves (primary or push/pull waves) and S-waves (secondary or shear waves).

The P waves travel faster than the S waves so they arrive at the seismograph first.

By looking at the difference in the arrival times of the two types of waves you can determine how far away the epicenter of the quake was from the seismograph.  If you do this for 3 different seismographs you can triangulate the exact location of the epicenter.  This is the lab the kids did this week, I gave them seismograms from three locations for a particular earthquake and they had to measure the arrive times off the data, figure the difference and then use a graph to find the distance from the epicenter.  Then they took a compass and drew a circle of that radius on the map.  Once they had done that for all three locations they could locate the epicenter where the three circles intersected.  Sometimes they get a small triangle instead of a point and that’s ok.  The quality of your end result really depends on your drawing compass, we didn’t  have any locking compasses and it would have made this lab much easier if we had.

We watched the videos above as well as the ones below during class.

 

The lab we did was from a college course I taught many years ago but I found this updated version on the web. I skipped the bit about  magnitude since my students are pretty young and most haven’t heard about logarithms but they did know that an earthquake with  magnitude 7 is 10x worse than a 6, and 100x worse than a 5.

 

 

Physics 014- Rotational Motion

I spent half the class this week lecturing on rotational motion and trying to get across that it really isn’t very different than linear motion.  In linear motion we have displacement (x), velocity (v) , momentum (p), and force (F), while in rotational motion we have angular displacement (θ) , angular velocity (ω), angular momentum (L) and torque (τ). We went over moment of inertia and how its the equivalent of mass for linear motion, but varies depending on the object’s shape. The further the mass is from the axis of rotation, the harder it is to rotate since you have to go a great distance in the same amount of time. So a disk with all the mass on the rim, like a bicycle wheel, will be harder to rotate than a solid disk of the same size and mass because some of the mass is closer to the axis of rotation. To prove this we did an experiment with a variable inertia apparatus (bought at cynmar for $16)- basically two plastic disks with cubby holes inside where you can place heavy ball bearings. So you can put all the mass near the center or have09518594 it near the outer rim of the disk. You can also change the mass of the disk by putting in more or less balls.  The students set up a very shallow ramp and timed how long it took the disks to reach the bottom for various combinations of ball bearings.  As they predicted, when the mass was distributed far from the axis of rotation the moment of inertia was high and the disk took longer to reach the bottom of the ramp.  If the mass was clumped close to the axis of rotation then it rotated/rolled down the ramp faster. Increasing the overall mass of the disk also increased the moment of inertia and the time to get down the ramp.

IMG_1392

I don’t have a bicycle gyroscope so we watched the video by Vertasium Gyroscopic Precession.

And check out this demonstration with toliet paper.

http://aplusphysics.com/flux/aplusphysics/unrolling-toilet-paper/

Big History 013 – Layers

Today was all about layers, layers in the Earth and in the atmosphere.  As the kids arrived they started putting together a lift the flap type thing that showed the structure of the Earth.  The foldable is by Nitty Gritty Science.  IMG_1339

Once everyone was done putting that together we watched Everything You Need to Know about Planet Earth by In a Nutshell – Kurzgesagt.  

We didn’t watch this one in class, but its kind of cute and it would easy enough to make your own earth cake at home.

The Everything You Need to Know About Planet Earth video also talked about they layers in the atmosphere and the  Earth: Power of the Planet  video series by BBC has an entire episode on the atmosphere so we watched the first 20  minutes or so of that on Netflix.  You can find bits and pieces of it on youtube:

The kids then made a model to scale of the layers of the atmosphere in their notebook. I had already cut the paper to size so they just had to glue them in the right order and label each layer.  Like illustrations of the solar system, posters of the layers of the atmosphere are rarely to scale  and show the atmosphere extending out to distances twice as far as the surface of the earth, while in reality its just a very thin layer around our planet.  For the model we made for the notebook, an earth to scale would have filled my living room!  The exosphere extends way past the edge of the book and most of the ‘air’ is in the lowest two layers, the troposphere and stratosphere.  Even in the stratosphere you would need an oxygen tank and protection against the cold and low pressures.

IMG_1335

 

 

 

 

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