Imagine you're enjoying a quiet day outdoors, perhaps sipping lemonade on your front porch, when suddenly — BOOM! A startling, thunderous noise reverberates through the air. No, it's not an explosion or a clap of thunder. It's something more awe-inducing: a sonic boom.
But what is a sonic boom, exactly? There's a whole science behind this auditory spectacle, and it involves aircraft flying supersonic, breaking the sound barrier, and creating a ripple effect in the air pressure waves around them.
The Basic Science: How Sound Waves Create a Sonic Boom
Imagine tossing a pebble into a pond; ripples will form in concentric circles, radiating outward. Sound waves function similarly, spreading out from their source. When an aircraft is flying at subsonic speeds, sound waves can easily disperse forward, and everything's chill.
Breaking the Sound Barrier
Now, think about a boat zooming across the pond so fast that it outruns those water waves, creating a singular, larger wave — a wake.
Similarly, when an airplane reaches supersonic speeds, it surpasses the speed of sound, currently traveling at approximately 700 mph (1,127 km) in air at sea level. This is when the aircraft "breaks" the sound barrier.
Birth of the Sonic Boom
As the aircraft maintains supersonic speed, all the sound waves that should've dispersed in front of it pile up and form shock waves. When these pressure waves combine, a single shock wave forms. A sonic boom is born, rolling across the sonic boom path like an acoustic carpet, making its presence known in the sonic boom impact area below.
Factors Affecting Sonic Booms
Altitude and Flight Path
The sonic boom path depends on the aircraft's altitude and flight path. The higher the aircraft flies, the greater the horizontal distance the sonic boom will cover, also known as the boom's lateral spread.
Air Temperature and Pressure
As the air temperature decreases with altitude, it can affect how the shock wave forms. Temperature gradients help bend the path of the sonic boom, making it less intense over greater distances. Additionally, air pressure at different altitudes can influence the shape of the sonic boom carpet.
The aircraft's length and speed relative to the speed of sound can alter the sonic boom's characteristics. Most fighter-sized aircraft produce a double boom, while larger aircraft might generate more complex boom patterns.
Realistic Flight Conditions
Under more realistic flight conditions, factors like the aircraft flight track, sea level and air temperature can affect the lateral boom spread and its impact area.
Sonic Boom FAQ
What does the term 'sonic boom' mean?
A sonic boom is the sound produced when an object, often today's supersonic aircraft, moves faster than the speed of sound. This rapid movement creates shock waves that manifest as a loud, booming noise. So, when you hear a sonic boom, it's often a fighter jet or a space shuttle, whizzing by at speeds that distort the natural spread of sound waves.
Why is a sonic boom so loud?
A sonic boom doesn't just tap you on the shoulder; it roars in your ear. Why? It's because numerous pressure waves merge to form a single shock wave. This N wave boom travels faster than sound and has the energy range to disturb the air molecules, resulting in a loud, impulsive noise similar to a cracking sound.
Can a sonic boom hurt you?
Though the strongest sonic booms can sound startling, their peak overpressure usually varies to only a few pounds per square foot — well below the structural damage thresholds accepted by the Federal Aviation Administration (FAA). However, the boom's intensity could potentially harm your hearing if you're too close to its source.
Is making a sonic boom illegal?
Since 1973, the FAA has prohibited sonic booms over densely populated areas, to prevent potential damage and disturbance. So, while it's not illegal everywhere, there are rules about where sonic booms are permitted.