Sound is an alternation of slightly higher and lower air pressure. At about 194 decibels, the low-pressure troughs hit zero: you cannot go below a vacuum. Beyond that point, the wave can no longer oscillate normally and becomes a shock wave, like those from explosions. Ordinary sound has a physical ceiling.
Cooled below −183 °C, oxygen turns into a pale blue liquid. Pour it between the poles of a strong magnet and, instead of flowing away, it hangs suspended between them. The reason lies in its unpaired electrons, which respond to the magnetic field. Liquid nitrogen, by contrast, is colourless and pours straight through.
In 2012, Felix Baumgartner jumped from a capsule hanging beneath a balloon, about 39 kilometres up. In that extremely thin air almost nothing slowed him down, and he reached around 1,358 km/h in free fall, or Mach 1.25. He became the first person to exceed the speed of sound with nothing but his own body.