How to teach amplitude and frequency

Why this matters

A student who plays guitar knows that a plucked string makes the sound, and still calls a higher note "louder". On a worksheet, that student can label amplitude and frequency on a drawing of a wave without ever hearing which one changed the note, and the teacher has to wait for quiz day to find out.

Amplitude and frequency in a sound wave

Amplitude is how tall a wave is. In a sound wave, a larger amplitude means the air is squeezed harder. Frequency is how many waves pass each second, measured in hertz. Students hear frequency as pitch, so a higher frequency is a higher note. Loudness depends on the wave's intensity, and the ear also hears some frequencies as louder than others (OpenStax College Physics). Intensity grows with the square of the amplitude, so a wave twice as tall carries four times the energy (OpenStax College Physics).

In the Flint activity, students get a sound wave maker Sparky built, with an amplitude slider, a frequency slider, a drawing of the wave and a Play button. The challenge is to make a note louder without changing which note it is. A student who moves the frequency slider gets asked to play both notes and compare the drawings. A student who makes the note louder with amplitude gets a harder question about how much energy a wave twice as tall carries.

Marcus's chat: make the note louder, not higher

Marcus is a middle schooler who plays guitar. He knows that sound comes from a vibrating string, and he uses "louder" and "higher" as if they mean the same thing.

The whole class gets the same activity: the same challenge, the same sound wave maker and the same energy question. Each student's chat is their own. Sparky opens with what it remembers about the student, and its next question depends on what the student just did with the sliders.

Sparky uses what it remembers about the studentSparky sends the student back to something they already triedA right answer gets a harder question

M

Marcus

Interest: Plays guitarStarting point: Says "louder" when he means higher

Sparky

Here's your challenge: make a note louder without changing which note it is. Say hi when you're ready to start.

Marcus

hi, im ready

Sparky

You play guitar, so you hear notes change all the time. Here's the Sound Wave Maker. Use the sliders and press Play to explore. Make the note louder without changing which note it is, then tell me what you changed.

Marcus

i moved the frequency from 440 up to 660 and pressed play. its louder now

Sparky

Good exploring. Play 440, then 660, and listen closely. Did the note itself change, or just the volume? Look at the wave drawing too. Did the waves get taller, or closer together?

Marcus

i played 440 again and then 660. the 660 one sounds higher, like moving up the neck of my guitar. the waves got closer together, not taller

Sparky

Exactly right. Higher frequency means a higher pitch, just like moving up the neck. So frequency changes which note it is. Which slider might make it louder without changing the note?

Marcus

i put frequency back to 440 and moved amplitude from 0.5 to 1. now its louder and its still the same note. the waves got taller but stayed the same distance apart

Understanding check

That's it: amplitude makes it louder without changing the note. If the wave is twice as tall, does it carry twice the energy?

Marcus

yeah twice as tall so twice the energy

Sparky

Here's a hint. Think about your guitar. When you pluck a string twice as hard, does it only take twice the effort?

Marcus

way more than twice. i have to pull the string twice as far and it pushes back harder the farther i pull it. so is it 4 times? like 2 times 2

Sparky

Yes, four times the energy. You worked it out from your own guitar. A wave twice as tall carries 4 times the energy, which is why a really loud strum takes way more than twice the effort.

Made the note louder with amplitude, then worked out that twice as tall is four times the energy

When Marcus said the higher note was louder, Sparky didn't correct him. It asked him to play both notes and look at the drawing, and he found that the waves got closer together, not taller. The energy question came only after he made the note louder with amplitude. When he answered twice, Sparky pointed him to his own guitar instead of giving the answer.

Marcus is an example student, and Sparky's replies are shortened.

What Flint did for Marcus

• Sparky remembered that Marcus plays guitar and opened the challenge with it, so he didn't have to explain himself first.
• The activity came with a wave maker Sparky built: two sliders, a drawing of the wave and a Play button that plays the note out loud.
• When Marcus moved the frequency slider, Sparky asked him to play both notes and look at the drawing instead of telling him which slider to use.
• After he got the slider right, Sparky asked an understanding check about energy, and gave him a hint from his guitar when he answered twice.

A teacher can't do this by hand for 30 students, and Sparky does it in every student's chat.

Who mixed up louder and higher, and who worked out the energy

When students finish, Sparky grades each chat against the activity's rubric: whether the student tells amplitude from frequency by sound and by the drawing, and whether they explain the energy. The activity page shows who needs help right now, what the class does well, and what to practice next.

Set up the activity for free

The sound wave activity is in Flint's public library, with the wave maker, Sparky's guidelines, greeting and a rubric already written. Open it, select Use activity to copy it into a free Flint account, and move it to a class. In the activity's Preview tab, select Try session myself to test the activity as a student before you assign it.

For more science activities, see Flint for science.