Air Molecules at Mach 1: Understanding Collisions and Net Velocity

[scumhearted]

If molecules generally move at sound speed, given they are accelerated at Mach 1, does this mean there are less arbitrary collisions? or less collisions in general and more molecules move in the direction of mach 1 speed??

 

[Whovian]

in the direction of mach 1 speed??

Let me just tell you that this phrase means nothing. Speed isn't velocity.

 

[0xDEADBEEF]

At the equator the air moves at mach 1.4 due to the rotation of the earth. What is your question again?

 

[Whovian]

At the equator the air moves at mach 1.4 due to the rotation of the earth.

Well, wrt the centre of the Earth.

 

[phinds]

At the equator the air moves at mach 1.4 due to the rotation of the earth. What is your question again?

This sounds like you are saying that at the equator, there are 1000 mph winds. Really?

 

[Whovian]

This sounds like you are saying that at the equator, there are 1000 mph winds. Really?

I think they're saying the air molecules move at 1000 mph wrt the centre of the Earth, not the surface.

 

[phinds]

I think they're saying the air molecules move at 1000 mph wrt the centre of the Earth, not the surface.

Ah ... got it. Seems meaningless. EVERYTHING moves at that speed on that basis.

 

[Drakkith]

If molecules generally move at sound speed, given they are accelerated at Mach 1, does this mean there are less arbitrary collisions? or less collisions in general and more molecules move in the direction of mach 1 speed??

The air will have more collisions as the compression wave passes through, since the air is compressed.

 

[0xDEADBEEF]

The point is that you ask what happens when air moves at that speed, which is probably not what you want to know. Maybe you want to know what happens in a supersonic shock wave, or in an explosion, or when you have supersonic flow around objects or ...

What happens at the speed of sound isn't really a good question.

Oh and to pick up on Whovian: with respect to the sun its mach 88 :)

 

[rcgldr]

The average speed of air molecules is well above the speed of sound, about 1750 kph versus 1235 kph., but the net velocity is zero (in a no wind condtion) since the molecules are mostly bouncing around with no net movement. In the outer edges of the atmosphere, a very small percentage of hydrogen atoms achieve escape velocity.