At what speed does something like metal begin to heat up?

[Pseudo-Onkelos]

I am excluding things that travel through the atmosphere. I take it when air becomes compressed (I think that's the word), it becomes hotter. Metals I guess would start glowing and rocks would burn away. So I'm wondering when something would begin to heat up. Is it hypersonic? If so, at what Mach number is this?

[Vannak]

Things that travel at high speeds don't inherently heat up, they do it because of friction with the air. Friction increases as speed increases, though. generally it's related to the velocity or the square of the velocity, the fluid dynamics, and the type of fluid.

[SmallTownGuy]

Vannak is right about ordinary speeds, but supersonic flow is a bit weird. When the space shuttle Columbia exploded, it was flying at about Mach 22.8 (and had already slowed from Mach 24). Its wing temperatures should have been about 2880F, about 90% of which was due to adiabatic compression of the supersonic air, not due to friction.

[Cogent Dream]

It depends on atmospheric composition. What is the metal travelling through? If it's a vacuum then it won't heat up.

[Pseudo-Onkelos]

Vannak

Things that travel at high speeds don't inherently heat up, they do it because of friction with the air. Friction increases as speed increases, though. generally it's related to the velocity or the square of the velocity, the fluid dynamics, and the type of fluid.

So I was wondering at what speed this friction becomes noticeable. Or is it just fiction that makes the friction noticeable by having a glowing red shock wave?

[Pseudo-Onkelos]

Cogent Dream

It depends on atmospheric composition. What is the metal travelling through? If it's a vacuum then it won't heat up.

Through air. I caught myself saying "atmosphere" because I guess that's used colloquially to refer to the ozone layer. So I'm excluding the ozone layer and referring to air.

[Cogent Dream]

Pseudo-Onkelos

Cogent Dream

It depends on atmospheric composition. What is the metal travelling through? If it's a vacuum then it won't heat up.

Through air. I caught myself saying "atmosphere" because I guess that's used colloquially to refer to the ozone layer. So I'm excluding the ozone layer and referring to air.

I don't think anyone here can give you an exact answer. It also depends on the angle (hence space shuttles must orbit before entering at the exact angle required so that the shuttle doesn't fall apart). The shape of the metal plays a bit part too as it can act to distribute heat and reduce friction better due to the aerodynamics (a long thin object will heat up much slower than a big chunk).

[Vannak]

Pseudo-Onkelos

Vannak

Things that travel at high speeds don't inherently heat up, they do it because of friction with the air. Friction increases as speed increases, though. generally it's related to the velocity or the square of the velocity, the fluid dynamics, and the type of fluid.

So I was wondering at what speed this friction becomes noticeable. Or is it just fiction that makes the friction noticeable by having a glowing red shock wave?

Its really particular to the kind of object your looking at, as well as the temperature, density, and viscosity of the fluid, and probably more factors than that.

It's totally impossible to figure out how hot something will get only based on speed.

[BlackShadow03]

Pseudo-Onkelos

Vannak

Things that travel at high speeds don't inherently heat up, they do it because of friction with the air. Friction increases as speed increases, though. generally it's related to the velocity or the square of the velocity, the fluid dynamics, and the type of fluid.

So I was wondering at what speed this friction becomes noticeable. Or is it just fiction that makes the friction noticeable by having a glowing red shock wave?

It is not impossible to have a temperature probe reading the heat built up by friction on your theoretical object. However, there are too many variables to just pick out a speed at which heat begins to occur. Shape, angle, material, density of the air, what gases compose said air, ambient temperature, and probably a few more variables that I am missing.