Sound Waves (Moises Garcia)

Title: Investigating Sound Waves using Audacity (Waves and Electromagnetic Radiation)

Principle(s) Investigated: Wavelength, Period, Frequency, and Amplitude in sound.

Standards : PS4.A: Wave Properties A simple wave has a repeating pattern with a specific wavelength, frequency, and amplitude. (MS-PS4-1) A sound wave needs a medium through which it is transmitted. (MS-PS4-2).

PS4.C: Information Technologies and Instrumentation Digitized signals (sent as wave pulses) are a more reliable way to encode and transmit information. (MS-PS4-3)

MS-PS4-1. Use mathematical representations to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.

Sound Energy S5-6:29 Generate a sound and identify the path of vibration from the source to the ear. Understand that sound in produced by vibrations in materials that set up wavelike disturbances that spread away from the source.

Materials: One Laptop per Team and Audacity (Free Sound Program. Click to download)

Procedure: Download the procedures and Questionare here.

Use the Sound Lab Speadsheet

to record your data.

Student prior knowledge: What prior concepts do students need to understand this activity?

Waves’ properties using common vocabulary: Amplitude, Frequency, Period, Wavelength, and Speed.

Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.

Students will be exploring the the concepts of Amplitude, Frequency, Period, Wavelength, and Speed through a sound lab. Students will be generating sound using various mediums like the voice and tunning forks. They will then attempt to explain a changes in Amplitude, Frequency, Period, and Wavelength and how that was accomplished. Below you can find the definitons and a way to calculate Frequency, Period, and Wavelength.

Amplitude is the maximum extent of a vibration or oscillation, measured from the position of equilibrium.

Wavelength, Period and Frequency

A graph of the air pressure at a certain point might look like this:

The arrow indicates one cycle of the sound. The time it takes to complete a cycle is the period. Frequency is the inverse of this, the number of cycles in a second. The distance sound travels during one period is the wavelength. All this is related by the formulas:

The upside down y is lambda, which stands for wavelength. P is period, f is frequency, and s is the speed of sound.

The reason we have to be aware of this relationship is that our ears are sensitive to frequency, which we perceive as pitch, but the world works mostly by wavelength. For instance, a trombone manipulates wavelength directly: when the temperature changes, the trombonist must adjust what he does to get the proper pitch.

A 1000 Hz tone has a wavelength a bit under one foot. The wavelength of 440 hz is 2.57 ft or 75.9 cm.

Questions & Answers: Give three thought-provoking questions and provide detailed answers.

How are sound waves produced?

1. Vibration of an object is what produces sound waves. The vibrating object moves in one direction and compresses the air directly in front of it. As the vibrating object moves in the opposite direction, the pressure on the air is lessened so that an expansion, or rarefaction, of air molecules occurs.

How can we describe a sound wave?

A sound wave is a type of pressure wave caused by the vibration of an object in a conductive medium such as air. When the object vibrates, it sends out a series of waves which can be interpreted as sound. For example, when someone hits a drum, it causesthe membrane of the drum to vibrate, and the vibration is transmitted through the air, where it can reach the ear of a listener. Vibrations travel at different speeds through different media, but cannot travel through a vacuum.

What are some ways to determine the speed, frequency, period and wavelength of a sound wave

model?

See Wavelength, Period and Frequency above.

A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. Why do compressions and rarefactions occur?

These compressions and rarefactions result because sound vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations.

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

Speech science (aucustics):

The production of speech is a highly complex motor task that involves approximately 100 orofacial, laryngeal, pharyngeal, and respiratory muscles. Precise and expeditious timing of these muscles is essential for the production of temporally complex speech sounds, which are characterized by transitions as short as 10 ms between frequency bands and an average speaking rate of approximately 15 sounds per second. Speech production requires airflow from the lungs (respiration) to be phonated through the vocal folds of the larynx (phonation) and resonated in the vocal cavities shaped by the jaw, soft palate, lips, tongue and other articulators. Speech is transmitted through sound waves, which follow the basic principles of acoustics. The source of all sound is vibration. For sound to exist, a source (something put into vibration) and a medium (something to transmit the vibrations) are necessary.

Music and Instrument Production (organology):

Click on the link for a explanation of the science of instruments.

Click here to see the frequencies of different musical notes.

Below find a simple way to create your own tuning chime

Wireless Communication:

Radio waves, microwaves, infrared and visible light are all used to carry information, which can be sound, pictures or other data. The information is called the signal. It is added to an electromagnetic wave called the carrier wave so that it can be transmitted. When the wave is received the carrier wave is removed and the signal is reconstructed. There are two types of signal, analogue and digital.

An analogue signal changes in frequency and/or amplitude continually in a way that matches changes in the voice or music being transmitted.

A digital signal has just two values – represented as 0 and 1 (or on and off). The signal is converted into a code of 0s and 1s. It becomes a stream of 0 and 1 values. These pulses are added to the carrier wave and transmitted. After the signal is received it is decoded to recover the original signal.

Read more at http://revisionworld.com/gcse-revision/physics/waves/wireless-communications#6L57gZJWG34wRgRR.99

Radio waves are used for broadcasting radio and TV programmes. Anyone with a receiver can tune it to the radio frequency to pick up the signal.

When radio stations use similar transmission frequencies the waves sometimes interfere with each other. Medium wavelength radio waves are reflected from the ionosphere so they can be used for long distance communication, but not for communicating with satellites above the ionosphere.

Microwaves

The transmitter and receiver must be in line of sight, (one can be seen from the other), so they are positioned high up, often on tall masts. They must be close together so that hills, or the curvature of the Earth, cannot block the beam.

Signals are sent to and from satellites, which relay signals around the Earth. This may be for TV programmes, telephone conversations or monitoring the Earth, for example weather forecasting.

Maximise Your Marks - Make sure you can compare the use of microwaves and radio waves. In ‘compare’ answers refer to both, for example microwaves pass through the ionosphere, but medium wave radio waves do not.

Diffraction

Diffraction is the spreading of a beam through gaps and around corners. The maximum effect occurs when the gap has a similar size to the wavelength.

Radio waves of about 5 m are diffracted by large buildings. Radio waves of 1 km are be diffracted around hills and through valleys, so they are able to reach most areas and are suitable for broadcasting.

Microwave beams of a few centimetres do not spread round corners or around hills. This is why the transmitters and receivers must be in line of sight. When microwaves are transmitted from a satellite dish the wavelength must be small compared to the dish diameter to reduce diffraction. This means that, compared to radio waves, microwaves can be sent as a thin beam.

Analogue and Digital Signals

Radio waves, microwaves, infrared and visible light are all used to carry information, which can be sound, pictures or other data. The information is called the signal. It is added to an electromagnetic wave called the carrier wave so that it can be transmitted. When the wave is received the carrier wave is removed and the signal is reconstructed. There are two types of signal, analogue and digital.

An analogue signal changes in frequency and/or amplitude continually in a way that matches changes in the voice or music being transmitted.

A digital signal has just two values – represented as 0 and 1 (or on and off). The signal is converted into a code of 0s and 1s. It becomes a stream of 0 and 1 values. These pulses are added to the carrier wave and transmitted. After the signal is received it is decoded to recover the original signal.

Read more at http://revisionworld.com/gcse-revision/physics/waves/wireless-communications#CIcqbgDyAZedqEqe.99

Photographs:

Fig. 1: Mr. Garcia's waveform from audacity

Fig. 2: Correlation between energy vs wavelength through different wave types.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.