Physical Science, Module 6, Earth and the Lithosphere, Part B

Module 6, Part 1
Play  Quizlet.  Just scroll down and click on Physical, then scroll to find the Module you want.
Plastic Rock - a non-Newtonian fluid

We mixed a 1 lb. box of cornstarch with 1½-2 cups of water.
First we only added a small amount of cornstarch at a time, getting it smooth before adding more.  They tried the whisk first, but gave up and just used their fingers.
They loved it!
I heard, "Cool!"  "Look at this!"  "Here, hold it like this - roll it in a ball."  "Hold your hands below mine and we'll make a waterfall."
The only way they would stop was it was time to leave.  =(
They made handprints in it, rolled it into a ball, smacked it, dragged their fingers through it, whatever they could think of.  JohnDavid even bounced a ball on it!  It is easier to pull a spoon out slowly than jerking it, which would apply force.

We did this experiment to show how the thick liquid part of the mantle, called the asthenosphere, behaves under the pressure of the earth.  A scientist named Andrija Mohorovicic studied seismic waves (vibrations from earthquakes) and came to the conclusion that about 20 miles beneath the earth's surface, there was a drastic change. That border is now called the Mohorovicic discontinuity, or Moho.  This marks the beginning of the boundary between the earth's crust and the beginning of the earth's mantle.

Scientists eventually found more about the composition of the earth's layers through indirect observation, just as Andrija Mohorovicic did.  The rock of the mantle is mostly silica, but the properties of that rock are incredibly different.  The matter in the mantle is more densely packed than the crust.  And deeper into the core, it is even more tightly packed.  The temperature also increases the deeper you go.  At the Moho, the temperature is about 930º F, while the lower portion of the mantle gets as hot as 4,000° F.

The pressure increases also.  By the time you reach the bottom of the mantle, the pressure is about 1.4 million times that of atmospheric pressure!

The high pressure and temperature of the mantle causes the rock to have some interesting properties.  It behaves more like a thick syrup, flowing slowly around the mantle.  When subjected to an abrupt force, the "syrup" hardens into a firm solid.  After the force passes, the rock resumes its flowing state.  Scientists call this rock plastic rock.

"Plastic Rock - Rock that behaves like something between a liquid and a solid"


To illustrate this, we made a non-Newtonian fluid.  "A non-Newtonian fluid is a fluid which cannot be described by a single constant viscosity (a measure of resistance). Most commonly, the viscosity changes with the applied shear stress." 
The simple definition is that it doesn't stay liquid, but under pressure, can become thicker/more solid, just like Plastic Rock.
►How do you think the man was able to get out?
By jumping?  That would apply force as he jumped up.
Stepping up like a ladder?  If he did it slowly, he would be able to raise his foot, but unless he was able to keep a jumping-in-place motion with that one foot, it would sink while raising the next foot.
I'm sure he needed help!  (2,500 lbs of cornstarch - whew!)

"The asthenosphere is solid even though it is at very hot temperatures of about 1600° C due to the high pressures from above. However, at this temperature, minerals are almost ready to melt and they become ductile and can be pushed and deformed like silly putty in response to the warmth of the Earth. These rocks actually flow, moving in response to the stresses placed upon them by the churning motions of the deep interior of the Earth. The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back."

I think this experiment may have been in the 2nd Edition.  Michelle had it posted on her blog.
Um, I believe my kids were a bit messier!!!
The cousins left at 11:00.  It is now 2:00.  My kids are still going by the bar occasionally and playing with the Plastic Rock.  =)