In famous photos, a white cone surrounds a fighter jet. It is not the moment of "breaking the sound barrier": at high speed, pressure drops sharply in some areas around the aircraft, the air cools and its moisture condenses. This cloud can form below Mach 1, and many supersonic flights show none at all.
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.