Frequency Simulation — ClassAdapt
What the simulation shows
The screen is divided into two live panels that update together at every frame.
Left — Particle of Medium. A glowing cyan sphere moves up and down on a vertical track, representing a single particle of the medium as a wave passes through it. A fading trail of ghost spheres follows it, showing where it has recently been. A green arrow pulses from the sphere in the direction of motion — it grows longer when the particle is moving fast (near the rest position) and shrinks to nothing at the top and bottom of its oscillation (where it momentarily stops). A green ring flashes outward from the sphere every time a new cycle begins, syncing visually with the click sound. The frequency readout f = X.X Hz sits at the bottom of the panel. The +A and −A markers show the amplitude limits, and a dashed line marks the rest position.
Right — Oscilloscope. A scrolling trace shows the last four seconds of the particle’s displacement — exactly as a real oscilloscope would. The time axis is marked 0s through 4s and the vertical axis shows +A, 0, and −A. At low frequency (0.5 Hz) two slow, wide crests fill the window. At 8 Hz, 32 tightly-packed cycles compress into the same space. This is the simulation’s central demonstration: the four-second window never changes, but the number of complete waves visible in it equals the frequency.
A yellow double-headed arrow bracket above the trace spans exactly one period T, with a label showing T = X.XXX s — updating live as the slider moves. Below the oscilloscope screen, two info rows sit in clearly separated panels:
- Row 1:
f = X.X Hz(cyan) ·T = X.XXX s(amber) ·T = 1 ÷ f(white) - Row 2:
~N complete waves per second (= frequency in Hz)(green) — a live counter that physically counts completed cycles in real time
Sound. The Clicks button sends a short pop through the speaker at the start of every cycle — one click per complete wave. At 1 Hz, students hear one click per second. At 4 Hz, four clicks per second. They can close their eyes and count the clicks to verify the number shown on screen.
Suggested Class Activity
“Seeing, hearing, and counting frequency”
Duration: 25–30 minutes | Level: GCSE Physics Y9–11 | Prior knowledge: basic wave definitions
1. What is one hertz? (4 min)
Open the simulation at f = 1 Hz with sound on and labels on. Ask students to watch the oscilloscope for 10 seconds in silence.
“Count how many complete waves you can see in the 4-second window. Write it down.”
Answer: 4. Then:
“Now count the clicks for 5 seconds. How many clicks?”
Answer: approximately 5. Then ask:
“What do those two numbers — 4 waves in 4 seconds, 5 clicks in 5 seconds — both tell you?”
Expected: one wave per second. Confirm: that is what 1 Hz means. Write it on the board: 1 Hz = 1 complete wave per second.
2. Slider investigation (10 min)
Students work individually or in pairs through this table. They change the slider, observe, and record. Sound must be on for the “clicks in 5 s” column.
| Frequency | Waves visible in 4-s window | Period T (from screen) | Clicks counted in 5 s |
|---|---|---|---|
| 0.5 Hz | |||
| 1 Hz | |||
| 2 Hz | |||
| 4 Hz | |||
| 8 Hz |
After completing the table, ask:
“What happens to T as f increases? Double the frequency — what happens to T?”
Expected: T halves. Guide to: T = 1 ÷ f (shown in the info bar on screen). Ask students to verify this with one row from their table.
“What happens to the oscilloscope trace as frequency increases?”
Expected: more waves appear in the same 4-second window. More waves per second = higher frequency.
3. The blind test (5 min)
One student (or the teacher) sets a frequency without telling the class. Hide the labels (press 🏷 Labels). The challenge:
“Count the waves in the 4-second window. Divide by 4. That is the frequency.”
Or, with sound on:
“Count the clicks in 10 seconds. Divide by 10. That is the frequency.”
Reveal the slider to check. Run two or three rounds, letting students take turns setting the frequency for each other to identify.
4. T = 1 ÷ f — the maths (4 min)
Turn labels back on. With the T bracket visible on the oscilloscope, demonstrate:
“The yellow bracket shows exactly one period — the time for one complete wave. At f = 2 Hz, T = 0.5 s. If I double f to 4 Hz, T becomes 0.25 s. As f goes up, T goes down.”
Give two short calculations:
- “A wave has a period of 0.4 s. Calculate its frequency.” — f = 1 ÷ 0.4 = 2.5 Hz
- “A wave has a frequency of 50 Hz. Calculate its period.” — T = 1 ÷ 50 = 0.02 s
5. Sound connection (3 min)
“The click you hear is one per wave. Real sound waves travel at 340 m/s and have frequencies between 20 Hz and 20 000 Hz. At 20 Hz you’d hear 20 clicks per second — the lowest rumble you can detect. At 20 000 Hz, 20 000 clicks per second blur into a high-pitched tone.”
Ask: “Why can’t we slow down a 440 Hz sound wave to see it on this oscilloscope?” — 440 Hz would put 1760 waves into the 4-second window. They’d be too close together to distinguish individually.
Adaptation notes for ClassAdapt
- Reduce Motion freezes both panels — the particle stops and the oscilloscope trace pauses. Students can read the static labels without competing motion, and the T bracket stays visible for as long as needed
- The live counter in row 2 (
~N complete waves per second) is particularly useful for students who struggle with the abstract formula — they see the count updating in real time and can directly connect it to the definition of hertz - The click sound is the most powerful scaffold: students who find the oscilloscope visually busy can close their eyes and count clicks instead, arriving at the same frequency value through a completely different sensory channel
- The blind test activity works well as a paired task — one student sets, one student counts — since it requires no reading or writing, only counting and a simple division