Since the speed of sound depends on the air, which changes at different altitudes, are “Mach” speeds dependent on the altitude? Or is it basically just like 100 °C is the same even at altitudes where water boils at a lower temperature (in that it is a fixed speed based on the speed of sound at sea level)?
@gedaliyah yes. Mach number is defined in terms of the local speed of sound, and that varies depending on pressure and temperature. I don’t know exactly how much, but several percent at least?