So, the test was difficult, and some of you did very well, but overall, I think we need to keep working on the material from the last section: reflection, refraction, diffraction, interference, standing waves and resonance. These are properties that all waves share, and so we will continue to discuss them when we learn about sound waves in music and when when we study waves in light. So first things first, watch Mr. Anderson's video: TAKE NOTES! In fact, jot down the six words above on six index cards, and add information as you watch...
(This is a video made for teachers to explain what it is they are supposed to be teaching.)
Textbook reading: Chapter 12, Sound section1. Fill in applicable worksheet from the packet handed out in class. - page 25 and 29. Be able to draw the ear from memory.
Lastly, research homemade musical instruments for ideas. Focus on an instrument which can play different pitches (notes) rather than only rhythm, and don't do an instrument where you fill up glass containers with water, since we will be doing this in class.) We will also talk more about this on Thursday, if you haven't come up with anything by then. Google, pinterest, or youtube, "homemade musical instruments". Your parents might be willing to "pitch" in for supplies (get it?) and as you recall, I have lots of PVC pipe, in case that helps (3/4").
And here is a short paragraph on what causes earthquakes. Notice that the names of the types of waves, compressional and transverse, are different. Can you tell which is which?
What causes earthquakes?
You might think Earth is a giant lump of rock, but you'd be wrong—it's more like a freshly
boiled egg: there's a hot, molten core bubbling away inside a
surprisingly thin outer crust. The countries we live in feel like
they're safely anchored on solid rocky foundations, but really
they're fixed to enormous rocky slabs called tectonic plates that can
slide around on the molten rock beneath. Imagine living your life on
an eggshell!
Earthquakes happen at places called faults (or fault lines) where the jagged
edges of two tectonic plates grind against one another. Most
earthquake activity happens in the middles of the oceans where plates
are pushing apart on the floor of the sea. Some of the most violent
earthquakes happen around the edges of a huge tectonic plate in the
Pacific Ocean, forming an intense area of activity known as the Ring
of Fire (so-called because there are many active volcanoes there
too).
Tectonic plates are constantly moving—in incredibly slow motion—and we don't even notice most
of the time. But every once in a while two grinding plates will suddenly
jolt into a new position. The energy released by this movement
creates an earthquake. It starts at a point inside Earth called the
focus where the moving plates are in contact, then travels
through the ground as very low-frequency sounds called shock waves
or seismic waves. The greatest damage happens at a place
called the epicenter, which is the point on Earth's surface
above the focus. Earthquakes continue until all the energy released
at the focus has been safely dissipated. Even then, there's still a
chance that further earthquakes, known as aftershocks, will
happen for some hours or even days afterward.
Seismic waves travel in two very different ways. Some of them, known as primary waves
(or p-waves), vibrate the ground in the direction in which the waves
themselves are moving. They travel in a similar way to ordinary sound
waves by alternately squeezing and stretching the ground in patterns
known as compressions and rarefactions. Waves like this are called
longitudinal waves and travel at incredible speeds of around 25,000
km/h (15,500 mph). There's another kind of seismic wave known as a
secondary wave (s-wave) that travels only half as fast. Unlike
p-waves, s-waves travel by making the ground vibrate up and down as
they move forward. It's because seismic waves travel at such
amazing speeds—broadly speaking, as fast as a rocket taking
off—that we get so little time to avoid quakes. Earth's diameter is
a little under 13,000 km (8,000 miles) at the equator, so a really
fast p-wave can theoretically shoot from one side of the planet to
the other in less than half an hour! Artwork: As s-waves travel forward, they shake the
Earth up and down or from side to side (at right angles to the direction
of motion). P-waves shake the Earth back and forth in the same
direction in which they're moving. An s-wave is
an example of a transverse wave; a p-wave is an example of a
longitudinal or compression wave.
This brings us to the end of chapter 11; there will be a test on Mondayon the material covered in the textbook. If you have questions, write them down; I will answer them at the beginning of class.
Thank God! It's Good Friday... and homework is limited. Please read chapter 11, section 2 - Wave Properties, for Monday's class. Take notes/make illustrations. And have a great Easter - You are all invited to Open Door's Good Friday service at Pioneer Park - David Harmon is speaking and Jesse & Jadon leading worship, Friday at noon.
Here are the two videos that I could not make work in class, the first one tells you another reason magnets are so amazing, and the second one tells you that it's not just about cool toys.
To prepare for Thursday, read in your textbook Chapter11, section 1, The Nature of Waves, take notes and answer the section 1 assessment questions on page 331 in your science journals.
When it was discovered, serendipitously, that an electric current induced a magnetic field in a wire, the question was asked, Could a magnetic field return the favor? And yes, with a lot of clever determination, Michael Faraday invented the generator, which he called the Dynamo, how cool is that name? Faraday demonstrated that a changing, or moving, magnetic field would induce an electric current. This is called electromagnetic induction.
Read your textbook, chapter 8, section 3: Producing Electric Current, taking notes/illustrate the main ideas and vocabulary listed under "As You Read" on page 240. And fill in the worksheets from class. After reading about generators, watch these videos:
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Reminder: Do the worksheets handed out in class to reinforce your understanding of the textbook!
