What Is A Sonic Boom? Why Breaking The Sound Barrier Creates A Sonic Boom

What Is A Sonic Boom? Why Breaking The Sound Barrier Creates A Sonic Boom

Breaking the sound barrier and creating a
sonic boom tends to be associated with fighter jets travelling at incredibly fast speeds,
but what is a sonic boom, and why does going faster than the speed of sound create a boom? Firstly, you need to understand what sound
is and how it propagates. Sound waves travel fastest through solid materials,
then liquids and then gasses. Unlike light, sound waves are mechanical waves
whereas light is a transverse electromagnetic wave which means that sound needs a medium
to travel though. On average, the speed of sound at sea level
is 340 metres per second, in water it is 1,433 metres per second and in a solid such as diamond
the speed of sound is 12,000 metres per second – 35 times faster than the speed of sound
in dry air. The speed of sound in a medium also varies
with temperature as the change in temperature affects the density of a medium. There are two properties which affect the
velocity of a sound wave: elastic properties and density, with this relationship being
described by this equation. Sound travels faster through steel than rubber,
as steel has higher elastic properties. The elastic properties relate to the tendency
of a material to not deform when a force is applied to it and to also maintain its shape. At the particle level, rigid materials have
molecules with strong forces of attraction for each other. The greater the elasticity and the lower the
density of a medium, the faster sound will travel through that medium. Although solids such as steel are far denser
than air, steels elastic properties are much greater meaning that sound transverses through
a solid medium such as steel faster than a gaseous medium such as air. When an object is moving through the air for
example, it creates pressure waves at the speed of sound around the object – such
as how a boat does when it travels through water as it creates bow and stern waves. When such object travels faster and faster,
the pressure waves begin to not be able to get out of the way of each other, causing
them to build up, compress and eventually merge into a shockwave. Essentially when something breaks the sound
barrier it creates compressions faster than the compressions can move away from it and
they end up piling on top of each other. It is a common misconception that when you
go supersonic that you only hear one boom from the transition from subsonic to supersonic,
but the boom is continuous for as long as you are going supersonic. This means that if an aircraft is approaching
you at supersonic speeds you will not hear any sound from the aircraft as it is travelling
faster than the sound it can produce, meaning you will only hear the sound after the aircraft
has travelled overtop of you. Sustaining supersonic flight does come with
its issues with aerodynamic heating occurring meaning that aircraft need to be designed
with materials such as stainless steel or titanium to sustain supersonic flight as some
parts of the aircraft can hit hundreds of degrees. For those not into guns, bullets break the
sound barrier with boring regularity. The sound difference between a supersonic
and subsonic bullet is noticeable as you’ll hear now. When bullets enter the transonic region, the
shifting of the centre of pressure causes the amplification of static and dynamic instability
causing the angle of attack and yaw of the bullet to potentially dramatically change
which is impossible to compensate for, and can cause bullets to impact on their sides
instead of at the tip and decrease overall accuracy. Bullets can however enter into the transonic
region with no problem, but the ability of such a bullet to do so is quite unpredictable. It might sound as though breaking the speed
of sound is unreachable unless you have a supersonic plane or a gun around you, but
with just the flick of a whip – you too can break the speed of sound. Thank you for watching and be sure to subscribe.


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