if you are traveling 800 knots at different altitudes, the “Mach” figure changes depending on how high you are?

Question

It’s easier to go Mach 2 at 50000 feet than it is at 25000 feet. Or so I hear.

In: Physics

Answer 1

Aerospace engineer here. “Mach” is not a set number – it is a ratio of your speed to the speed of sound in the air you are in.

Sound requires molecules to bump into each other to transmit. Generally, at higher altitudes, the air is thinner and it is more difficult for air molecules to bump into each other. Therefore, the speed of sound goes down with altitude.

If you’re traveling at 800 kts at a lower altitude where the speed of sound 800 kts, you’re travelling at Mach 1. If you’re traveling at 800 kts where the speed of sound is slower, let’s say 400 kts, you’re at Mach 2.