What exactly is a "mach"?

Question

I know it's some sort of measurement for speed, right... but how much exactly is it? Is there a limit to how many there are? What mach number is sound and light?

Answer 1

There is not really anything called "a Mach" - what you are referring to is the Mach number, the ratio of your current airspeed to the speed of sound at current conditions. You would never say "how many Mach". Your speed may be Mach 3, but you are not doing 3 Machs.



Mach 1 (the speed of sound) is not a constant. As others have pointed out, the speed of sound at sea level at standard conditions is 761 MPH, but it slows as temperature drops, and varies with air density.



You may be wondering why we bother our selves with it, since the speed varies a great deal. After all, you can not easily use the Mach number to figure out how long a flight will take.



A critical change occurs as you near Mach 1: below the speed of sound air acts like an incompressible fluid, the air traveling around the plane will maintain a constant air density. As you reach the speed of sound the air molecules can no longer get out of each others way quickly enough and start to pack closer together and form shock waves. This causes a huge increase in drag, using a great deal of power The changing pressure as the air compresses and forms shock waves can cause the plane to lose control if the plane is not designed to deal with these effects. It was this sudden change in flight characteristics that led to the idea of "a sound barrier".



A note to eferell: I know who Ernest Mach is, I'm pretty sure he was mentioned during the 3 years of aerodynamics I took (and took at school that had what was at one point one of the largest supersonic wind tunnels in an academic environment.)

Answer 2

Yes, John R, there really is a Mach. Ernst Mach(1838-1916) to be exact. He was an Austrian physicist who studied gas dynamics and the effects of the speed of sound on an object. Note this was long before any man made objects except bullets traveled faster than the speed of sound. He and his son developed a method to actually photograph the shock waves in the air made by bullets and artillery projectiles. His calculations on the compressibility of gas in front of a fast moving object led modern airplane manufacturers to design aircraft with the least amount of frontal area to decrease compressibility. When an aircraft reaches the speed of sound, the air is compressed so much in front of the aircraft that a sonic boom is heard when passing through. The ratio of the aircraft speed and the speed of sound is called 'Mach number' in honor of Ernst Mach. Since the speed of sound is dependent on the thickness of the air, the speed of sound varies with altitude, being faster at higher altitudes. Here is an article on Mach Number you might find interesting:



http://www.grc.nasa.gov/WWW/K-12/airplane/mach.html

Answer 3

Mach number is the airspeed divided by the speed of sound. Thus, Mach 1.0 is exactly the speed of sound, Mach 2.0 is twice the speed of sound, and Mach 0.5 is half the speed of sound.



The speed of light is approximately Mach 881,252 at 15° Celsius (the speed of sound varies with air temperature).

Answer 4

Mach is the speed of sound. So if a plane is 2 Mach, it is 2 times the speed of sound. However, the speed of Mach is different depending on what altitude you are.

Answer 5

1 mach or Mach 1 is the speed of sound in the medium in question. 761.2mph is right for sea-level?



But it's been recorded to slow to 315.72 meters per second at minus 12 degrees C due somewhat to differences in air density. At 35 degrees C it's been recorded to travel at 351.96 meters per second.



Likewise the speed of light is the relative speed of light through that course it must go to get to the eye. AND as was proved by Einstein, large objects curve space, and thus light. So the term speed has less meaning. It's all relative to how far the wave must travel, as is dictated by gravity wells. Light goes allot faster than sound. Light travels at approximately 186,282 miles per second.



These figures from wickedpedia (sic).

Answer 6

a Mach number refers to velocity relative to the speed of sound with Mach 1 being the speed of sound. sound travels at 761.2 mph at sea level with standard atmospheric pressure and temperature and light travels at a constant669,600,000 mph or 879663.7 mach

Answer 7

Mach is the measure of 1 times the speed of sound. There is no limit but mach 8 is the fastest speed that i know we have reached on earth. Light speed is measured in light years.

Answer 8

mach or mach number is the ratio of the speed of an object over the speed of sound at an altitude which the object is flying. I.E if you're flying at 250knots at SSLC the mach number would be different if you're flying 250 knots at 35000 ft. formula: a/c speed/speed of sound at an altitude

Answer 9

To clarify the peed of sound and the effects of altitude. Sound travels faster through a dense object than through the air. The speed of Sound it approx 13% slower (662 mph), at 35,000 feet than at sea level

Mach is the speed of sound and is easily calculated it is used as a universal reference for speed just like Greenwich mean time is universally used as a time reference at 1 pm (1300) Zulu time regardless of what time zone or where on the planet you are it is. 1 pm in Greenwich England

Answer 10

Mach is the speed of sound. Mach 2 is twice the speed of sound. Mach 0.85 is 0.85 the speed of sound. Mach 0.50 is half the speed of sound.

Mach 1 is 1225 kph/761.2mph/661.470842 knots

100 kph is mach 0.09414715.

100 mph is mach 0.151515152

Answer 11

"Mach" is the speed of sound as indicated on the airspeed indicator. M2 is twice the speed on sound. M.75 is 3/4 the speed of sound.

Answer 12

Mach is the speed of sound, 762.1 miles per hour.The speed of light is 186,000 miles per second.

Answer 13

Here's how you do it.

http://tinyurl.com/25vdsxx