New Topic: Sound Friday, 14 September 2018 Learning question: What is sound?

Learning objectives Explain that sound waves are a form of energy transfer from a source through a medium to a receiver. Describe and explain how sound is transmitted through a medium and the factors affecting it. Explain why sound needs a medium through which to travel. Describe the wave motion of a longitudinal (sound) wave. Use a slinky spring, tuning fork and ukulele to demonstrate the characteristics of sound. Describe the structure of sound waves using the terms compression, normal air pressure and rarefaction. Describe a sound wave in terms of frequency, pitch, amplitude, loudness and wavelength.

Key words: Sound energy Medium Receiver Longitudinal Sound wave Compression Rarefaction Pressure Amplitude Wavelength Frequency

What are sound waves? Sound waves are longitudinal waves that must pass through a medium. Sound is a form of energy. The sound from the person’s mouth travels through air – this is the medium for sound to travel through Longitudinal waves travel lengthwise in the direction the sound has come from

How does sound travel? https://youtu.be/C9NlDtFNVc0 Start at 12.05

How does sound travel? Sound is transmitted (passed) through a medium when vibrating particles move sideways and collide with each other. During the collision, energy is passed from one particle to another. The particles in sound waves bounce off each other and so move backwards and forwards.

How sound travels… 4) The ear then sends a message to the brain Air molecules 2) The vibrations pass through air by making air molecules vibrate 3) These vibrations are picked up by the ear 1) An object makes a sound by vibrating

Task Complete the activities on pages 4 and 6 of your sound booklet. Make sure that you read the information on these pages and answer the questions fully. This will help you to study for the test 

Why does sound need to travel through a medium? This energy is transferred (moved) from one particle to the next when they collide. If there were no particles (no medium) then there would be nothing to attach the energy to and there would be no collisions. This means there would be no way to transport the energy from the source to the receiver.  I can’t hear a thing.

Learning objectives Explain that sound waves are a form of energy transfer from a source through a medium to a receiver. Describe and explain how sound is transmitted through a medium and the factors affecting it. Explain why sound needs a medium through which to travel. Describe the wave motion of a longitudinal (sound) wave. Use a slinky spring, tuning fork and ukulele to demonstrate the characteristics of sound. Describe the structure of sound waves using the terms compression, normal air pressure and rarefaction. Describe a sound wave in terms of frequency, pitch, amplitude, loudness and wavelength.

Types of Waves Longitudinal waves Transverse waves Sound waves and waves in a stretched spring are longitudinal waves. In longitudinal waves, the vibrations are along the same direction as the direction of travel. Light and water are examples of transverse waves. In transverse waves, the vibrations are at right angles to the direction of travel.

Features of a wave There are three key features that help us to understand the properties of a wave. These are the: Amplitude Wavelength Frequency

Amplitude As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. Take care, the amplitude is not the distance between the top and bottom of a wave.

Wavelength The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.

Frequency The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). The closer together the waves are, the higher pitched the sound will be. The further away the waves are from each other, the lower pitched the sound will be

Features of a wave There are three key features that help us to understand the properties of a wave. These are the: Amplitude Wavelength Frequency

Task Complete the worksheet on features of a wave.

Features of a wave part 2 Sound waves are different from the type of waves that we have looked at before (transverse waves). Sound waves are longitudinal waves and so look different. Sound waves are compression waves. This means that they “bunch up” together (compress) and then spread out again (rarefaction).

Features of a wave part 2 Compressions – places in sound waves where the particles are packed closely together Rarefactions – places in sound waves where the particles are spread apart The distance from one compression to another is the wavelength

The air particles become tightly compressed due to increased pressure The air particles become spaced due to decreased pressure. This is called rarefaction The air particles become tightly compressed due to increased pressure

Amplitude Amplitude is the loudness of the sound wave. Soundwaves that are loud have very large (sharply defined) compressions and rarefactions. E.g. compressions are very close together and rarefactions are spread far apart.

Can you write a sentence to describe what is happening in this image?

How tuning forks make sound As the tines on a tuning fork vibrate, they disturb the air near them. As the tine swings to the right, it forces the air molecules near it closer together. This means that the air particles are much closer together, or in an area of compression. The opposite is true for rarefactions

Task Complete pages 7 – 12 of your booklet. Your teacher will help you with some of this work and demonstrate high and low pitch frequencies.

Learning objectives Explain that sound waves are a form of energy transfer from a source through a medium to a receiver. Describe and explain how sound is transmitted through a medium and the factors affecting it. Explain why sound needs a medium through which to travel. Describe the wave motion of a longitudinal (sound) wave. Use a slinky spring, tuning fork and ukulele to demonstrate the characteristics of sound. Describe the structure of sound waves using the terms compression, normal air pressure and rarefaction. Describe a sound wave in terms of frequency, pitch, amplitude, loudness and wavelength.