Since 2019, Avogadro's number is no longer measured: it is fixed at exactly 6.02214076 × 10²³. A mole is therefore precisely that many atoms or molecules. That is roughly the number of molecules in 18 grams of water, a single sip. Counting them at one per second would take more than a million times the age of the Universe.
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.