Posts Tagged ‘waves’

Waves Unit Intro

When I was teaching at a college prep high school last year, my advisor showed me how he always introduces waves via the pendulum. For the life of me I can not remember if that is how I was introduced to waves, but I think it’s fabulous! It was a great lesson today, so I thought I would share:


I have this tiny little pendulum (pictured above) one of my students made me last year, so I set it up and had my students brainstorm every type of physics they observed. We went through the whole list (velocity, centripetal motion, friction, gravity, momentum, energy, etc) and discussed each one for a short bit. Next, I described the importance of pendulums and we brainstormed a list of pendulums in “real life”. Some classes were more creative than others, but the point was clear that pendulums are everywhere.

At this point, I asked students what determines the period (time for one cycle) of the pendulum. The usual mass, gravity, amplitude, and string length came into play, so we attacked one at a time:

  • MASS – the pendulum is essentially in free fall and we know that mass in negligible in free fall, so no need to deal with it here either.
  • GRAVITY – will affect every pendulum equally, so it can not affect individual pendulums diferently.
  • AMPLITUDE – to test this we timed 10 oscillations at a low amplitude and 10 at a high amplitude. The times were almost exact, so the students understood that it does not affect the period.

Therefore, the length is the only variable to affect the period of the pendulum.

Vocab came to play here as we defined amplitude (height of pendulum), period (time it takes for one cycle to occur, measured in seconds), and frequency (number of cycles that occur in a given time period, measured in Hz). I wrote the definition of period and frequency on the board as equations as well as the inverse relationship between them. The students then did a few sample problems from the textbook (Hewitt Conceptual Physics – awesome resource!).

To finish up the period, we graphed the position-time graph of the pendulum and the light bulb went off and the kids realized the connection between the pendulum and waves. They drew a transverse wave and labeled the anatomy in order to conclude the lesson.

We’ll pick up with types of waves and the wave equation tomorrow.

Sound Unit

I haven’t uploaded all my lessons from this unit yet – I need some more time to make them pretty :)

Here’s the gist of the unit though, along with one of the lesson plans.

PRE-UNIT LESSON – Still part of the general waves unit, this lesson discusses standing waves and the Doppler Effect.

UNIT DAY 1 – Sound Intro: Includes discussion of Doppler Effect, sonic boom, sound traveling in a medium, and sound reflection (echo) if time allows.

UNIT DAY 2 – Standing Waves & Pitch

UNIT DAY 3 – Sound & Wave Review: Give students time to cover sound reflection (echo) and diffraction before reviewing homework, packets from day 2, and a gallery walk with the KWL charts from wave unit.

UNIT DAY 4 – Quiz.

Since we did a comprehensive general wave unit, transferring that information to the sound unit was straightforward and we only needed a few days. Using the last day of the wave unit to create a seamless transition to sound was extremely helpful; students felt they had something to offer since we had already discussed Doppler Effect and Sonic Boom.

Earthquakes and Tsunamis

Coincidental to the earthquake in Chile and tsunami in Hawaii, my class is studying waves. On Wednesday we even studied the refraction of water waves and discussed tidal waves. I am glad we discussed the formation of tidal waves before this occurred so my students have a scientifically literate knowledge of what is happening.

We watched this video of an annual tidal wave and discussed that large waves are created when a large amount of energy in the deep-sea is forced into a more shallow area, causing a higher amplitude and faster wave velocity.

The important difference between a tidal wave and a tsunami is the initiation of the energy of the wave. Tidal waves are generated the same way as tides – by the changing distance between the earth and the moon. Tsunamis are caused mainly by earthquakes.

Most people think of a tsunami as a The Day After Tomorrow-sized wave that will take out all of lower Manhattan.

I guess the possibility of that happening one day is not out of the question, but tsunamis are not classified by being at least 30 meters tall. In the case of this tsunami, the amplitude of the waves have not increased more than 1 meter every 20 minutes. This might be the greatest change in amplitude that is observed.

The biggest concern with this storm is that the major changes in tides could cause an extremely caustic environment for the flora and fauna within the ocean.

The reason I’m writing tonight is not to teach you about tsunamis, but to stress the importance of using every opportunity to provide our students with an education rich in scientifically literate experiences. Watching the news today, I have heard too many people panic that a tsunami means ginormous wave that will inevitably destroy everything. I shutter at the idea that these people went to school for at least twelve years and never had a science lesson that corrected the “2012” inspired misconceptions about tsunamis.

This is why I teach science – to give students an opportunity to learn about the world around them.

NOTE: It may seem that your content area is not suitable for teaching about tsunamis (especially if you’re not a geology or earth science teacher!), but if I could work it into a physics lesson, you can work it into any science course! A biology class could discuss  the effect of the tsunami on the ecosystem of the Hawaiian Pacific Ocean, as could an environmental course.  A chemistry class could discuss how the changing chemical composition of the ocean will affect the organisms. Any way you do it, you’re giving your students a priceless exposure to scientific current events!

Human Transverse and Longitudinal Waves

As promised, here are the videos from this week’s lesson on waves. The kids are making transverse and longitudinal waves.

I love how different the cultures of the two classes are!

Light & Waves by Dot Physics

Another great post by Rhett at Dot Physics! It’s always difficult to teach the wave-particle duality of light since students (and even teachers) struggle with the abstract reasoning involved. Rhett does a fantastic job with his illustrations and explanations of light as a wave. I’m definitely using this with my students.

Read the article “Light and Waves – at a basic Level”

Corks, Ears, and Eyes, Oh My!

I recently read this question, I’m curious to hear what you think!

Someone (maybe Helmholtz) suggested the following way of thinking about how our eyes and ears interpret light and sound. Imagine that you are standing at the edge of a lake. If you use your eyes, you can get an enormous amount of detailed information about the lake and its surroundings: trees on the shore, birds on the lake, cars and trucks traveling on a road nearby…. However, suppose you could only look at two corks floating side by side near you on the surface of the lake. How much could you deduce about the lake and surroundings by simply observing and interpreting the movements of the two corks? In fact, that is what your ears (and brain) do if you think of your eardrums as the corks!

Explain and evaluate the validity of the contrast between seeing and hearing described above. What characteristics and properties of light and sound does it depend upon? What is (or are) the key difference(s) between the behavior of light and sound, and between the operation of our eyes and ears, that give rise to the dramatic contrast between seeing and hearing described in the above paragraph.

Please leave your comments!

Single Wave Pulse Videos

As I was trying to create an assignment regarding transverse and longitudinal waves the other day, I stumbled upon these videos of a single wave pulse. The anatomy of the waves are very clear and, I suspect, a great teaching tool!

Transverse Wave