It’s easier to go Mach 2 at 50000 feet than it is at 25000 feet. Or so I hear.
In: Physics
Air density has a big effect.
At lower altitudes, the air is more dense – this makes it harder to travel at speed, as the plane needs to push more air out of the way, which requires more fuel to do.
At higher altitudes the air is a lot thinner, so the plane can cut through the air much more easily.
As an analogy, think about moving a knife through a jar of honey – it is hard work, and the honey resists the movement of the knife quite a lot. This is like moving at low altitudes.
Then try moving your knife through a bowl of water – you can swish your knife about with no effort at all. This is like moving at high altitudes.
The this is the main reason why commercial jets fly at around 35,000 feet – this altitude is a good balance between flying high enough to reach the thinner air and save fuel, while being low enough that the life support equipment needed to keep passengers comfortable and safe isn’t too prohibitively expensive.
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