Category Science

Some aircraft can travel faster than the speed of sound. They travel ahead of the sounds they make. This produces a build-up of sound energy behind them that becomes a shock wave, heard as a sonic boom.

Have you ever seen a plane fly overhead at a supersonic speed? If so, you may have heard a loud “boom” as it passed by. Did it explode? Nope! You can still see it flying. Then what was that sound? It was a sonic boom.

A sonic boom is a loud sound kind of like an explosion. It’s caused by shock waves created by any object that travels through the air faster than the speed of sound. Sonic booms create huge amounts of sound energy.

When an object moves through the air, it makes pressure waves in front of and behind it. Have you ever seen a boat move through water? The bow waves (front) and stern waves (back) are similar to the invisible pressure waves created by an object as it moves through the air.

These pressure waves travel at the speed of sound. How fast is that? Pretty fast! Sound travels at different speeds through different types of materials. It also varies by altitude and temperature.

At sea level and 68° F, the speed of sound through air is about 761 miles per hour. At an altitude of about 20,000 feet where the atmosphere is thinner and colder, sound travels at about 660 miles per hour.

Austrian physicist Ernst Mach developed a method of measuring airspeed relative to the speed of sound. If a plane if flying at the speed of sound, it is said to be going Mach 1. A speed of Mach 2 would be twice the speed of sound.

As an object, such as an airplane, travels faster and faster, the pressure waves can’t get out of the way of each other. They build up and are compressed together. Eventually, they will form a single shock wave at the speed of sound.

The sonic boom we hear caused by an airplane flying at Mach 1 usually takes the form of a “double boom.” The first boom is caused by the change in air pressure as the nose of the plane reaches Mach 1, and the second boom is caused by the change in pressure that occurs when the tail of the plane passes and air pressure returns to normal.

As long as an airplane travels at Mach 1 or faster, it will generate a continuous sonic boom. All those in a narrow path below the airplane’s flight path will be able to hear the sonic boom as it passes overhead. This path is known as the “boom carpet.”

If you’re wondering about how pilots handle sonic booms, they actually don’t hear them. They can see the pressure waves around the plane, but people on board the airplane can’t hear the sonic boom. Like the wake of a ship, the boom carpet unrolls behind the airplane.

Picture Credit : Google

Most sounds are not pure sounds of a single wavelength and frequency. Other frequencies are mixed in with the sound, creating the particular texture and tone of an individual voice or instrument. These frequencies are called harmonics.

When a musical instrument is playing a note, what we are actually hearing is the fundamental pitch, which is the pitch being played by the instrument, accompanied by a series of frequencies that are usually heard as a single composite tone. Those frequencies that are integer multiples of the fundamental pitch’s frequency are called harmonics. If a musician causes one of these harmonics to sound, without sounding its fundamental frequency, it is called playing a harmonic. This can be a little bit confusing, so let’s backtrack for a second. First off, we need to understand frequency.

Frequency is the rate at which a vibration occurs. This is measured in hertz (Hz), which is calculated by finding the number of vibrations per second. For example, a frequency that is vibrating 100 times per second would be described as having a frequency of 100Hz. When a pitch is produced, it creates a sound wave that vibrates at a specific frequency, the fundamental frequency, but it also causes a variety of other, higher frequencies to vibrate. These vibrations will be referred to as composite frequencies because they are a result of the vibrations of the fundamental frequency.

When the fundamental frequency and all of its composite frequencies are perceived by a listener, they are rarely heard as separate pitches. A listener will more likely perceive all of the frequencies wrapped together to form what we refer to as a composite tone. Any time an instrument produces a pitch, it will inherently produce a range of composite frequencies that add to the richness of the tone, and allow us to differentiate sound qualities, such as the difference between the way a violin sounds, and the way a guitar sounds. Ok, now that we’ve established a bit about how a pitch is heard, let’s make it even more complicated!

In order to discuss harmonics, we need to add one more component to the mix . . . MATH! Mathematics plays a big part in discussing harmonics, but lucky for us, none of it will get overly complex. For a composite frequency to be considered a harmonic, its frequency must be an integer multiple of the fundamental frequency. Don’t worries if that come on a little strong; we’re going to elaborate a bit on it now.

Let’s start with a hypothetical fundamental frequency of 100Hz. If we were to multiply it by any integer, our result would be considered an integer multiple of the fundamental frequency. In contrast, if we have a composite frequency, divide it by the fundamental frequency, and the result is an integer, then that composite frequency is an integer multiple. This is elaborated on a bit in the table.

Musical notation is a way of writing down musical sounds so that a singer or instrumentalist can reproduce them as the composer intends. As well as showing the pitch and length of the sounds, the notation gives information about how the notes should be played.

Musical notation, visual record of heard or imagined musical sound, or a set of visual instructions for performance of music. It usually takes written or printed form and is a conscious, comparatively laborious process. Its use is occasioned by one of two motives: as an aid to memory or as communication. By extension of the former, it helps the shaping of a composition to a level of sophistication that is impossible in a purely oral tradition. By extension of the latter, it serves as a means of preserving music (although incompletely and imperfectly) over long periods of time, facilitates performance by others, and presents music in a form suitable for study and analysis.

The primary elements of musical sound are pitch, or the location of musical sound on the scale (hence interval, or distance, between notes); duration (hence rhythm, metre, tempo); timbre or tone colour; and volume (hence stress, attack). In practice, no notation can handle all of these elements with precision. Most cope with a selection of them in varying degrees of refinement. Some handle only a single pattern—e.g., a melody, a rhythm; others handle several simultaneous patterns.

The position of staff notation as the first notational system to be described in this article acknowledges its international acceptance in the 20th century. As an indirect result of colonization, of missionary activity, and of ethno-musicological research—not because of any innate superiority—it has become a common language among many musical cultures.

Sounds travel as waves. It is the shape of the wave that determines the kind of sound that is produced. The pitch of a sound (whether it is high or low) depends on the frequency of the sound waves. The frequency is how many waves, or vibrations, the sound makes in one second. This is measured in hertz (Hz). One vibration per second is one hertz. How loud the sound is depends on the magnitude (or height) of its waves. The more energy the waves carry, the louder the sound. Loudness is measured in decibels (dB).

Sound energy travels in waves and is measured in frequency and amplitude. Amplitude measures how forceful the wave is. It is measured on a Logarithmic scale and reported in decibels or dBA of sound pressure. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can reach about 120 dBA but is often at 100 dB.

Sounds that are 82 dBA or above can permanently damage your ears when exposed for a long period of time. The more sound pressure a sound has, the less time it takes to cause damage. For example, a sound at 85 dBA may take as long at 8 hours to cause permanent damage, while a sound at 97 dBA can start damaging hair cells after only 30 minutes of listening.

Frequency is measured in the number of sound vibrations in one second. A healthy ear can hear sounds of very low frequency, 20 Hertz (or 20 cycles per second), to a very high frequency of 20,000 Hertz. The lowest a key on the piano is 27 Hertz. The middle C key on a piano creates a 262 Hertz tone. The highest key on the piano is 4186 Hertz.

How loud a sound seems to depend on who’s listening. A young person playing rock up in their bedroom might not think their music is loud, but their parents in the room down below might have other ideas. In other words, how loud things seem is a subjective thing and not something we can easily measure. However, what makes one sound seem louder than another is the amount of energy that the source of the sound is pumping towards the listener in the form of pressure variations in the air. That’s the intensity of the sound.

Meters that measure sound levels work by calculating the pressure of the sound waves traveling through the air from a source of the noise. That’s why you’ll sometimes see them referred to as sound pressure level (SPL) meters. Devices like this give a measurement of sound intensity in units called decibels as we mentioned before. Telephone pioneer Alexander Graham Bell first devised this scale.

Sonar uses ultrasonic sounds to find out where and how far away something is. This is called echo-location. The sounds are transmitted and bounced back by the object. The time that passes between the transmission and the reception of the reflected sound tells how far away the object is. Sonar is used particularly at sea to establish the depth of water beneath a boat.

Sonar, short for Sound Navigation and Ranging, is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves. NOAA scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the seafloor such as shipwrecks, and map the seafloor itself. There are two types of sonar—active and passive.

Active sonar transducers emit an acoustic signal or pulse of sound into the water. If an object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer. If the transducer is equipped with the ability to receive signals, it measures the strength of the signal. By determining the time between the emission of the sound pulse and its reception, the transducer can determine the range and orientation of the object.

Passive sonar systems are used primarily to detect noise from marine objects (such as submarines or ships) and marine animals like whales. Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels that do not want to be found or for scientific missions that concentrate on quietly “listening” to the ocean. Rather, it only detects sound waves coming towards it. Passive sonar cannot measure the range of an object unless it is used in conjunction with other passive listening devices. Multiple passive sonar devices may allow for triangulation of a sound source.

It’s a fact well-known enough to be the tagline to the 1979 sci-fi horror blockbuster Alien: “In space, no one can hear you scream.” Or to put it another way, sound can’t be carried in the empty vacuum of space – there just aren’t any molecules for the audio vibrations to move through. Well, that is true: but only up to a point.

As it turns out, space isn’t a complete and empty void, though large swathes of it are. The interstellar gas and dust left behind by old stars and sometimes used to create new ones does have the potential to carry sound waves – we just aren’t able to listen to them. The particles are so spread out, and the resulting sound waves are of such a low frequency, that they’re beyond the capabilities of human hearing.

As Kiona Smith-Strickland explains at Gizmodo, sounds travel as molecules bump into each other, the same way that ripples spread out when you drop a stone into a pond: as the ripples get farther and farther away, the sound gradually loses its force, which is why we can only hear sounds generated near to us. As a sound wave passes, it causes oscillations in the air pressure, and the time between these oscillations represents the frequency of the sound (measured in Hertz); the distance between the oscillating peaks is the wavelength.

If the distance between the air particles is greater than this wavelength, the sound can’t bridge the gap and the ‘ripples’ stop. Therefore, sounds have to have a wide wavelength – which would come across as a low pitch to our ears – in order to make it from one particle to the next out in certain parts of space. Once sounds go below 20 Hz, they become infrasound’s, and we can’t hear them.

One example noted by Gizmodo is of a black hole, which emanates the lowest note scientists know about so far: it’s about 57 octaves below middle C and well below our hearing range (about a million billion times deeper than the sounds we can hear). You’d expect to be able to measure about one oscillation every 10 million years in a black hole sound, whereas our ears stop short with sounds that oscillate 20 times per second.

Back on our own planet, the sounds of very strong earthquakes are sometimes intense enough to make it out into space, and infrasound can carry on going where normal sound has to pull up.

For a short amount of time after the Big Bang (about 760,000 years), the Universe was dense enough for normal sounds to pass through it. And if you hear the sound of a planet or spacecraft exploding in a Star Wars movie, remember that the filmmakers are taking liberties: chances are you wouldn’t hear much of it at all.