*A Taste of Physics for the Weekend — No. 2*
To understand how the firecracker in the video keeps burning underwater, we first need to understand why water puts out fire in the first place.
Water extinguishes fire for 2 reasons:
- The fuel heats up, turns into a gas, and burns in a reaction with oxygen. Water drains heat away, cooling the fire to a temperature that can no longer sustain combustion.
- It cuts off access to oxygen, halting the chemical reaction and extinguishing the flame.
The firecracker in the video contains an oxidizer in its chemical composition — for example, potassium nitrate (KNO₃). The oxidizer continues to supply the oxygen needed for combustion even underwater.
A similar use of oxidizers can be found in ballistic missiles and spacecraft, where engine combustion continues even outside the atmosphere — with no available oxygen from the surroundings.
In terms of temperature, the firecracker burns at an exceptionally high temperature (over 1,000 degrees Celsius!). Water, by contrast, boils at a much lower temperature (around 100 degrees, depending on the atmospheric pressure at that location). This means the water surrounding the firecracker boils and evaporates faster than it can cool the firecracker sufficiently — and so it keeps burning.
#taste_of_physics