In heavy water, hydrogen is replaced by deuterium, an isotope whose nucleus carries an extra neutron. Its molecules weigh about 11% more. The result: an ice cube of heavy water, despite being ice, sinks in a glass of ordinary water. Chemically almost identical, the two waters differ mainly in their mass.
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.