How does vibrations cause sound

Set your phone back to the lowest volume and change the frequency of the tone that you are playing to a higher frequency. Repeat the activity, slowly increasing the volume for this new tone.

How is the new tone different? Does it sound higher or lower? How does the new tone affect the granules? Is the effect different than what you observed with the first tone? If so, in what way? What do you think causes the difference between the two tones? Extra: Repeat the activity, trying different tones.

Try to explore a wide range! Extra: Try the activity again, but this time replace the glass bowl with other household containers. Does a cake pan work? What about a vase? What about a metal or wood bowl? If you didn't see any results the first time, try using a deeper bowl, and try different sizes. Build a Cooler.

Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. When vibrations are slower, you hear a lower note. Describe how sound is produced.

How many different vibrations are needed to hear a sound? All objects have the potential to vibrate. Can we hear all of them? If a tree falls in a forest and there is nobody around to hear it, does it still make a sound? Teacher Tip: This demonstration is a good way to introduce the topic of sound. Details Activity Length 10 mins. In this demonstration, students use their bodies to model vibrations that lead to sound waves.

Three things vibrate when sound is created: the source object the molecules in the air or another medium e. Objectives Describe how sound is produced. Materials anything that makes a sound e. A sound wave enters the ear and is changed into nerve signals, which are interpreted by the brain.

As a given object vibrates or oscillates in air, for example, the air molecules near or around the medium will be moved back and forth in relation to the frequency and force of the vibration. If the vibration is strong and slow, like bass drum hit with a soft mallet, the sound will be loud and low in pitch, if the vibration is weak but fast, like a pin falling on a wooden floor, the sound will be soft and high pitched.

Once these vibrations are propagating through the air, can it be called sound? From one perspective the only thing that makes sound exist are ears, human or otherwise, and nervous systems and brains or ganglia to interpret and decode those vibrations into meaningful data — i.

It is an interesting idea to think about. Some argue that sound is sound is sound. A forest is a busy place, with many creatures in it, so even if there are no humans around, some kind of animal or bug will experience the vibrations and use that data to run away from, or investigate the noise, i. But if it just so happens that there are no creatures nearby to catch those waves with their auditory senses, and the energy merely propagates into nothing, does it make a sound at all?

Even more interesting is; if nothing is around to hear the tree fall, can we go one step further and say no tree fell at all if nothing experiences it? As sound travels through a medium, its energy causes the molecules to move, creating an alternating compression and rarefaction pattern.

It is important to realize that molecules do not move with the sound wave. As the wave passes, the molecules become energized and move from their original positions. During compression there is high pressure, and during rarefaction there is low pressure. Different sounds produce different patterns of high- and low-pressure changes, which allows them to be identified.

The wavelength of a sound wave is made up of one compression and one rarefaction. Sound waves lose energy as they travel through a medium, which explains why you cannot hear people talking far away, but you can hear them whispering nearby. As sound waves move through space, they are reflected by mediums, such as walls, pillars, and rocks.

This sound reflection is better known as an echo. This is due to the large rock walls reflecting your sound off one another.

So what type of wave is sound? Sound waves fall into three categories: longitudinal waves, mechanical waves, and pressure waves. Keep reading to find out what qualifies them as such. If you push a slinky back and forth, the coils move in a parallel fashion back and forth. Similarly, when a tuning fork is struck, the direction of the sound wave is parallel to the motion of the air particles.

A mechanical wave is a wave that depends on the oscillation of matter, meaning that it transfers energy through a medium to propagate. These waves require an initial energy input that then travels through the medium until the initial energy is effectively transferred. Examples of mechanical waves in nature include water waves, sound waves, seismic waves and internal water waves, which occur due to density differences in a body of water. There are three types of mechanical waves: transverse waves, longitudinal waves, and surface waves.

Why is sound a mechanical wave? Sound waves move through air by displacing air particles in a chain reaction. As one particle is displaced from its equilibrium position, it pushes or pulls on neighboring molecules, causing them to be displaced from their equilibrium.

As particles continue to displace one another with mechanical vibrations, the disturbance is transported throughout the medium. These particle-to-particle, mechanical vibrations of sound conductance qualify sound waves as mechanical waves. Sound energy, or energy associated with the vibrations created by a vibrating source, requires a medium to travel, which makes sound energy a mechanical wave. A pressure wave, or compression wave, has a regular pattern of high- and low-pressure regions.

Because sound waves consist of compressions and rarefactions, their regions fluctuate between low and high-pressure patterns. For this reason, sound waves are considered to be pressure waves. For example, as the human ear receives sound waves from the surrounding environment, it detects rarefactions as low-pressure periods and compressions as high-pressure periods. Transverse waves move with oscillations that are perpendicular to the direction of the wave.

Sound waves are not transverse waves because their oscillations are parallel to the direction of the energy transport; however sound waves can become transverse waves under very specific circumstances. Transverse waves, or shear waves, travel at slower speeds than longitudinal waves, and transverse sound waves can only be created in solids.

Ocean waves are the most common example of transverse waves in nature. A more tangible example can be demonstrated by wiggling one side of a string up and down, while the other end is anchored see standing waves video below. Still a little confused? Check out the visual comparison of transverse and longitudinal waves below. Create clearly defined nodes, illuminate standing waves, and investigate the quantum nature of waves in real-time with this modern investigative approach.

You can check out some of our favorite wave applications in the video below. What makes music different from noise? And, we can usually tell the difference between ambulance and police sirens - but how do we do this? We use the four properties of sound: pitch, dynamics loudness or softness , timbre tone color , and duration.

It provides a method for organizing sounds based on a frequency-based scale. Pitch can be interpreted as the musical term for frequency, though they are not exactly the same. A high-pitched sound causes molecules to rapidly oscillate, while a low-pitched sound causes slower oscillation. Pitch can only be determined when a sound has a frequency that is clear and consistent enough to differentiate it from noise.