In physics, a calorie is the energy that warms one gram of water by about one degree. The calories on food labels are actually kilocalories, a thousand times larger: enough to warm a litre of water by one degree. A 250-calorie chocolate bar therefore holds 250,000 calories in the strict sense. The SI unit is the joule, which labels also show in kilojoules.
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.