Guess the song
Pick a melody and title the video "Every bounce plays a note. Guess the song". The tune gets clearer as the bounces speed up.
HypnoSim / Growing Ball
The ball grows with every bounce
One small ball bounces inside a glowing circle. Every time it hits the wall it gets a little bigger and plays the next note of a melody. The bigger it gets, the less room it has, so the bounces come faster and the song speeds up on its own.
Create this video free →
A 15-second run with a random seed, simulated in your browser.
The video runs until the ball fills the circle, then ends on a flash and a big "FILLED!" with the exact time and bounce count. There is no fixed length to guess around: the ending is the result, so viewers watch to the last second.
How it works
- You set how much the ball grows per bounce and how big it starts. The seed decides the starting direction, so every seed gives a different bounce pattern.
- Each wall bounce plays the next note of the melody you pick (Ode to Joy, Twinkle Twinkle, Für Elise or Tetris), or of a MIDI file you import. Early on the notes are slow; near the end they come in a quick run.
- The ball changes color on every bounce, the circle shifts from cyan to pink as it fills, and a small ripple marks each hit on the wall. A fill percentage runs at the bottom.
- Growth is a fixed amount per bounce, so the video length comes from the physics: with the default setting the circle fills in about 25 seconds. A max length (90 seconds by default) is only a safety limit; if it is reached first, the video ends on "SO CLOSE" with the percentage filled. The same seed always gives the same video.
What you can customize
- Ends when the ball fills the circle
- Gravity & bounciness
- Growth per bounce
- Start size
- Melody (each bounce plays a note)
- 9:16 · 16:9 · 1:1 MP4 with sound
Video ideas
"How long until it fills?"
Lower the growth for a slower, tenser build, or raise it for a quick 15 second short. The final screen shows the exact fill time.
Comment bait
Ask viewers to comment the second they think it fills. The final screen shows the exact time, so everyone can check their guess.
Growing Ball FAQ
How do I make a growing ball bouncing video?
Open the Growing Ball template, pick a melody, roll a seed and export the MP4. The ball grows on every bounce and the video ends by itself on the FILLED screen once the circle is full.
Can I make the ball fill the circle faster or slower?
Yes. Raise "Growth per bounce" to fill sooner (a shorter video), lower it to fill later (a longer one). A bigger start size also makes it fill sooner.
Can I use my own song?
Yes. Import a MIDI file and each bounce plays its next note instead of the built-in melody. The notes are rendered into the MP4 in sync with the bounces.
Why does the music speed up?
As the ball grows, the space between it and the wall shrinks, so it reaches the wall more often. More bounces per second means more notes per second.