How are two objects heated by friction? Let’s say that we have two objects made of different materials, both at room temperature. Surfaces of the objects are rubbed together, producing frictional heat. Is the heat distributed evenly, i.e. will the surfaces of the two objects be at the same temperature after being rubbed? How does this depend on the materials?
 A: Friction generates vibrations which create sound waves.  Sound transmission occurs through molecular oscillations. The temperature of a substance is directly related to the energy of molecular oscillation; molecular oscillation ceases at absolute zero.  Sound wave absorption occurs through conversion to heat, which is absorbed by the interface materials.
The loud shrill sound of car tires braking obeys the inverse square law related to the distance from the sound source. Imagine the sound intensity 1mm from the sound of braking tires when it registers 90 decibels at 50 meters!   The high intensity of sound and its immediate conversion to heat energy as it is being absorbed fill our nostrils with the smell of burning rubber (Hamilton, Order in Chaos (2011): 71-77).
In fluid dynamics, in the phase of transition to turbulence, simple harmonic (SH) boundary layer oscillations appear. An oscillation is a vibration which produces a sound wave. SH oscillations in boundary layer air creates SH sound.  Turbulent spots, characterized by isolated spikes of in-phase oscillations (also intense spikes in sound waves) occur in late transition, followed by the emergence of many turbulent spots, high boundary friction and loud aerodynamic noise (Schubauer and Skramstad 1941).  It is probable that the intense heating of space re-entry capsules is related to intense sound generation, much of which may be inaudible ultrasound.
A thin layer of oil between two solid surfaces greatly reduces the heat of friction. The thinness of the oil drastically reduces the maximum amplitude of the oil boundary layer oscillations, reduces the sound generation and the heat energy creation by frictional sound (Hamilton 2011).
