When an object moves through the air faster than the speed of sound, it “breaks the sound barrier.” This transition to supersonic speeds involves significant aerodynamic changes. Understanding this phenomenon requires examining the speed at which sound travels and the physical effects that occur when an object surpasses it. This article will detail the speeds, measured in feet per second (fps), required for supersonic flight and its observable impacts.
Understanding the Speed of Sound
Sound is a vibration that travels through a medium as waves of pressure and rarefaction. Its speed is influenced by the medium’s properties. In air, the speed of sound is not constant; it changes primarily with temperature and, to a lesser extent, with humidity. Warmer air allows sound to travel faster because its molecules possess more kinetic energy, leading to quicker transmission.
Mach 1 defines the speed of sound. At sea level, under standard conditions (around 20 degrees Celsius or 68 degrees Fahrenheit), the speed of sound in dry air is approximately 1,125 feet per second (fps). At 0 degrees Celsius (32 degrees Fahrenheit), this speed decreases to about 1,086 fps. While humidity can slightly increase the speed of sound, temperature remains the most significant factor influencing its velocity.
The Phenomenon of Breaking the Sound Barrier
As an object accelerates and approaches Mach 1, it begins to catch up with its own sound waves. These pressure waves start to compress and pile up in front of the object. This accumulation creates a region of highly compressed air, increasing aerodynamic drag. Once the object exceeds the speed of sound, these compressed waves merge into a single, intense shockwave that trails behind it in a cone shape.
The “sonic boom” is the audible evidence of this shockwave reaching an observer. It is not a single event occurring only when the sound barrier is crossed, but a continuous effect generated as long as the object maintains supersonic speed. The boom sounds similar to an explosion or thunderclap due to the sudden change in air pressure as the shockwave passes. This rapid pressure change can be strong enough to rattle windows.
A visual effect associated with breaking the sound barrier is the formation of condensation cones, also known as vapor cones. These clouds of condensed water appear around the aircraft as it moves at or near supersonic speeds. The rapid drop in air pressure and temperature behind the shockwave causes water vapor in the air to condense into droplets, creating the temporary, cone-shaped cloud. This phenomenon is most noticeable in humid atmospheric conditions.
Examples of Transonic and Supersonic Travel
Supersonic aircraft are examples of objects designed to regularly exceed the speed of sound. Military fighter jets, such as the F-15 Eagle and F-16 Fighting Falcon, routinely operate supersonically. Historically, two passenger airliners, the Anglo-French Concorde and the Soviet Tupolev Tu-144, were also capable of supersonic flight, though both have since been retired. These aircraft were engineered to withstand the forces and heat generated during sustained high-speed travel.
Bullets often travel at supersonic speeds. Rifle bullets can range from approximately 600 to over 4,000 feet per second (fps), with many exceeding Mach 1. For instance, some .243 Winchester loads can surpass 3,260 fps, and certain .22-250 Remington loads are rated at 4,000 fps, significantly faster than the speed of sound. Even common .22LR rimfire cartridges can travel at about 1,070 fps, often exceeding the sound barrier.
The tip of a whip is another object that can break the sound barrier, creating a sonic boom heard as a distinct “crack.” As the whip is snapped, its tapering design allows energy to concentrate towards the tip, causing it to accelerate. The tip of a whip can reach speeds exceeding 1,100 fps, creating a shockwave and the characteristic sound. This makes the whip one of the earliest human-made objects known to achieve supersonic speeds.