# Mach 1 Speed. What Does That Mean?

When you hear someone say that a plane is traveling at Mach 1 what exactly does that mean?  It means that the plane is traveling at the speed of sound.  Mach 1 equals the speed of sound whereas Mach .5 is half the speed of sound and Mach 2 is twice the speed of sound.  That's some pretty cool general information to know, right?

Another cool thing about Mach numbers is that the speed of sound is not constant; it depends on temperature and altitude.  In other words, sound travels at different speeds depending on where it is traveling.  Here's a good trivia question to ask somebody:  If two planes are both traveling at Mach 1 can they be going different speeds?  If that somebody answers no, they would be wrong.

Here's some more information relating to our topic:  The word sonic is a synonym for Mach 1 and speed of sound.  So if you're traveling at sonic speeds, you're traveling alongside sound.

To watch Sonic the Hedgehog travel at the speed of sound check out the video below!

FYI:  The speed of sound (Mach 1) at sea level and 15o C (59o F) is 761.2 mph (340.3 m/s).

http://en.wikipedia.org/wiki/Mach_number

I never really gave thought to what "traveling at mach speed" actually meant. It is a phrase that seems to be thrown around quite a lot. I think I am going to try the trivia question on one of my friends this week. Before reading this blog post, I have to admit I would have gotten that one wrong. I am ashamed of that because I am about to graduate this semester with a master's degree in engineering! I also appreciated your video of Sonic the Hedgehog. I have an older brother, and I don't think it is possible to add up all the hours of my life I spent watching him play that video game. Definitely takes me back quite a few years!

I think it is amazing that we have been able to break the sound barrier for more than 60 years, when chuck Yeager did it in 1947.

This fact is good to know. So when an airplane has a speed rating of Mach 2, what does that mean? If they are at different altitudes and temperatures, what is the standard altitude and temperature that this speed rating is based on. Does it vary from aircraft to aircraft?