Simviation Forums

is mach 1 or the speed of sound your indicated air speed or your speed reletive to the ground  

IAS if I'm not mistaken.

i figured so like if i was standing in a 600 mph wind or how ever fast it is i would thereticaly break the sound barrear or the wind would  ;D

eventhough that situation is in every waymeterologicaly and phisicaly in posible. on earth adleast  ;D

Since the speed of sound is reliant on atmospheric conditions, I would say that the speed of sound is measured in true airspeed.

Speed of sound is a tricky little thing, at sea level its 661.5 kts however it also changes with temperature, Higher temperature, the faster the speed of sound is, just do a google search. But its usually refering to true air speed.

[quote]i figured so like if i was standing in a 600 mph wind or how ever fast it is i would thereticaly break the sound barrear or the wind would

[quote]So, if you stood in a Mach 1 wind, you'd be very unhappy, AND you would be breaking the sound barrier.

Chris is right, the wind cannot break the sound barrier since the wind is the medium the sound travels through. This sounds like some dodgy fourth dimension thread!

stood stationary (relative to the ground) in a mach 1 wind (ouch), you would technically be a supersonic object since any sound you emmited would be confined to the sonic cone directly downwind of you. This is such a complicated and irrelivent question lol!

Last year I did a whole thermodynamics module on this kinda stuff I just cant remember any of the terminologies or official theories and practices off the top of my head right now, and I dont have my notes with me

JB

Chris is right, the wind cannot break the sound barrier since the wind is the medium the sound travels through. This sounds like some dodgy fourth dimension thread!

I'm no scientist but I would argue with that. A fixed object cannot possibly break the sound barrier or anything else.

Academics delight in complicating things. If what you say is true my house is moving relative to the wind outside. This is a purely hypothetical question as we're not likely to experience a wind travelling at anything like the speed of sound. I sincerely hope not anyway.

The Mach number is commonly used both with objects travelling at high speed in a fluid, and with high-speed fluid flows inside channels such as nozzles, diffusers or wind tunnels.
http://en.wikipedia.org/wiki/Mach_number

Not sure I follow that. Movement is relative to the medium it's measured against, in this case the ground.

Movement is not always measured relative to the ground.  When an airplane is flying through the air it is measuring its speed relative to the air as all of its flight characteristics are only important with respect to the speed relative to the air.  Ground speed is only of interest in navigation.

When talking about the speed of sound you're talking about the speed that sound travels through something.  In this case the "something" is the air.  Let's say the speed of sound is 800mph (depends on air pressure, temperature, etc).  If there is a wind going North at 400mph then someone on the ground will measure sounds traveling north as going 1200mph and south as 400mph (with respect to the ground).  Someone in a hot air baloon floating along with the wind will measure sound going 800mph regardless of the direction (with respect to the wind).

So, breaking the sound barrier means exceeding the speed in which sound travels in the medium.  For the person standing on the ground they could break the sound barrier by traveling south at 400mph, or by traveling north at 1200mph.  But the person in the baloon always sees this person as traveling 800mph.

Want to get crazy?  Think about the being a passenger on the Concorde.  You're traveling faster than the speed of sound through the outside air.  But you can still hear the stewardess when she asks you if you want to freshen up your Martini.  Why?  Because you're brining your own cabin full of stationary air with you.  A person on the ground, if they could see the sound waves from that stewardess, would see those sound waves traveling in excess of the speed of sound relative to the ground!

This is why I get a chuckle out of the Lock On Modern Air Combat folks who proclaim how real the game is because the engine noises in the cockpit go away at mach 1.  As if an entire vibrating plane, and all the air in it would somehow become a very quiet place once you exceed the sound barrier!

If you stood in a Mach 1 wind you would indeed break the sound barrier.  Relative to the wind you'd be going faster than the speed of sound.  If you stood on the wing of the Concorde you would NOT be able to tell the stewardess that you wanted your Martini shaken, not stirred, no matter how loud you yelled.

Anyway, back to your windy day.  There's no difference between standing on the wing of the Concorde and standing in a plus Mach 1 wind on the ground (with the exception of the startled look on the faces of the livestock wizzing past you).  You're still breaking the sound limit.  And although you're not traveling across the earth's surface, you are moving very fast relative to our friend in the hot air baloon.

Academics delight in complicating things. If what you say is true my house is moving relative to the wind outside. This is a purely hypothetical question as we're not likely to experience a wind travelling at anything like the speed of sound. I sincerely hope not anyway.

Here's a simplification.  You're an engineer.  You want to know if the plane you designed will fly past Mach 1.  So you put a model of it in a Mach 1 wind tunnel.  Does that tell you anything about how the plane will fly at Mach 1 or is the data irrelevant because the plane isn't moving relative to the ground?

[quote]
Movement is not always measured relative to the ground.

I constantly break through the sound barrier just sitting in my comfy arm chair, travelling at a speed of approximately 1,000 miles per hour just rotating with the Earth....

Whilst zooming round the Sun I have to be strapped to my comfy arm chair travelling at a speed of 67,000 miles per hour......!

How's that for breaking wind breaking the sound barrier... ...?

Paul...Holding my hat on... ...!

We're not talking about an aircraft. That's the whole point. The speed of something on the ground is measured relative to the ground. There's no way a stationary object could break the sound barrier.

An object on the ground is not always measured relative to the ground.  Let's say you're on one of those fancy European high speed trains traveling 150mph.  You drop your pen, it rolls across the aisle.  The person across the aisle tosses it back to you at 10mph.  Do you duck and cover because the pen is traveling at 160mph and you don't want it to hit you?

A ship is coming in to the harbor against a five knot current.  There are two speeds which are critical to the pilot: the wind speed, and the speed the ship is making way through the water.  The pilot doesn't care how fast the ship is moving relative to land until he's right next to the dock.

Stationary object break the sound barrier in wind tunnels all around the world every day.