I was playing the game Osmos for iPad, and the soundtrack creates a low bass that vibrates my iPad. How do I achieve this effect? Here is the Link to the music . ( Soundtrack name : Gas Discovery) Possibly using garageband ?
Your iPad is vibrating because the note happens to be a pitch at which the iPad resonates.
Garageband has plenty of built-in sounds. "Deep round synth bass" would be a good one to start with (this is from desktop GarageBand... I guess there's something similar on iPad). Experiment with pitches. Too high, and it's not bass any more. Too low, and it's too low to hear, what's called sub-bass.
If you're intent on finding that resonant frequency, you may well need to try pitches that are in-between the semitones. Use pitch-bend, or find an app that plays continuously varying tones.
One trick that some people like, is to duplicate bass parts one octave lower than the audible part, so you can hear the higher version, and (when played on suitable speakers) feel the lower version in your body.