Properties of Sound Unit 13 Section 2

I.The Speed of Sound Sound can travel at different speeds depending on the media it is traveling through. Although sound travels quickly through gases (air), it travels faster through liquids and the fastest through solids. Temperature also plays a role in the speed of sound. i. The warmer the temperature, the quicker the sound waves travel.

II. Pitch and Frequency Frequency-The number of vibrations, or back-and-forth motions in a second Pitch is how low or high a sound seems to be. So, a wave with a high frequency(many crests) will have a high pitch. A wave with a low frequency(few crests) will have a low pitch.

Link to demonstrate Frequency and Pitch http://www.iknowthat.com/ScienceIllustrations/sound/science_desk.swf

Which example has the highest frequency?

III. The Doppler Effect The Doppler Effect occurs when the source of the sound (like an ambulance) or the observer (you) is moving. Example: As an ambulance passes by you, the siren’s pitch changes. That change in pitch is known as the Doppler Effect. http://video.search.yahoo.com/video/play?p=the+Doppler+effect&ei=UTF-8&vs=science.discovery.com&vid=0001300181352

The Doppler Effect

The Doppler Effect When the ambulance moves, the sound waves are going in the same direction, causing the compressions and rarefactions to be closer together - (a louder pitch). If you are standing in front of the ambulance, the pitch sounds high because it is coming towards you. After the ambulance passes you, the pitch seems low since the sound waves are not as close.

Doppler video examples http://science.howstuffworks.com/27963-assignment-discovery-doppler-effect-video.htm http://science.discovery.com/video-topics/space-videos/time-doppler-effect.htm

IV. What is Loudness? Loudness is a measure of how well a sound can be heard. The amount of force will change the loudness of a sound. More force = louder sound Less force = quieter sound For example, if you lightly tap a drum, you will hear a soft rumbling. If you were to bang loudly on the drum, you would hear a loud sound. e. Loudness is measured in decibels.

V. Loudness and Amplitude When you strike a drum with a lot of force, the drum is moving with more vibration and causes the air particle to move further from their rest position ( amplitude ). Therefore, the larger the amplitude, the louder the sound wave will be. The smaller the amplitude, the softer the sound wave will be. An amplifier is used to increase the amount of energy and make the sound louder.

VI. ‘Seeing’ Sound Sound waves are invisible, but by using an oscilloscope we can graph representations of a sound wave. In an oscilloscope, a microphone is attached and it changes the sound wave into an electrical signal. Then, the signal is graphed on the screen in the form of a wave.

Oscilloscope

Quickie Quiz The amplitude of a sound’s wave determines the sound’s Pitch Loudness Resonance Sound quality

Quickie Quiz The frequency of a sound wave determines: The type of interference The sound quality The loudness of the sound The pitch of a sound

Quickie Quiz The medium through which sound waves travel affects the: Sound quality Number of waves per second Amplitude of the waves Speed of the sound

Quickie Quiz The motion of either the listener or the source of a sound causes: Resonance Shock waves The Doppler effect echolocation