Tap water carries dissolved air and minerals. In an ice tray, water freezes from the outside in, and the growing ice pushes these impurities toward the centre. In the end they are trapped in the core of the cube as tiny bubbles that make it milky. Freeze water in a single direction and you get crystal-clear ice.
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.