When you go to your local petrol station, you buy in litres (except for Americans who buy in gallons. I mean, who does that except for them?😂). But did you notice that fuel in Formula 1 is actually calculated in kilograms?
A Modern Formula 1 Car can carry a maximum of 110kg of fuel although teams never fill the full tank to reduce weight. This is because liquids change volume under temperature which basically means the amount of fuel changes with the change of temperature.
It's also the same reason why fuel is measured by mass in Aviation (Aeroplanes). So, let's get into science part of this. The energy-volume ratio of fuel changes based on the fuel temperature whereas energy-mass ratio (specific heat of combustion) doesn't. Now if you measured the fuel by volume, you would have to make sure the fuelling takes temperature into account.
In regions like Middle East, where the temperature is higher, you would get a lot less energy stored into the fuel tank than a colder environment. Worst Case Scenario is that you think you have plenty of fuel when in fact you might run out before you finish the race. Also, the effect of added mass is simpler to simulate and predict than effect of added volume of fuel.
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