2 What is sound? Sound is a longitudinal wave In air, sound waves cause air particles to move back and forthIn areas where the particles are pushed together, compressions formIn between the compressions, particles are spread out. These are rarefactions.
3 Sound requires a medium While light waves do not require a medium, sound waves must travel through a mediumRemember that the material through which a wave travels is called a medium.For sound to be heard, sound vibrations must have air or some other kind of matter to travel through.
4 Fun fact: You cannot hear sound in outer space because there is no air or other matter to carry sound vibrations.Q: How do you think astronauts are able to talk to each other in outer space?The astronauts have devices in their helmets which transfer the sound waves from their voices into radio waves and transmit it to the ground (or other astronauts in space). This is exactly the same as how your radio at home works. Remember that radio waves are NOT sound waves - they are a form of electromagnetic radiation, and therefore can propagate through a vacuum.
5 What causes sound? Sound is caused by a vibrating object Examples: The vocal cords in your throat vibrate when you speak; tuning fork; musical instruments
6 How do we hear sound? Object vibrates Sound waves are sent. The outer ear “catches the sound waves”.The middle ear takes the sound waves and “vibrates” the eardrum.The inner ear sends the messages to the brain.The brain puts together the messages and you hear sound!Middle EarInner EarBrainOuter EarSource of Sound Waves
7 Sound travels through matter Sound can travel through solids, liquids, and gasesThe speed of sound depends on elasticity, density, and temperature of the medium the sound travels through
8 Sound travels through matter ElasticitySounds travel fastest in solids because the particles of a solid bounce back and forth quickly as the waves pass by (molecules have greater attractive forces between them)
9 Sound travels through matter DensityIn materials in the same state of matter (for example: 2 liquids), sound travels more slowly in denser mediumsWould sound travel faster in syrup or water?
10 Sound travels through matter TemperatureSound travels slower at lower temperatures than at higher temperaturesBecause at lower temperatures the particles of a medium move slower
11 Two important properties of sound: 1) Loudness2) Pitch
12 Loudness Loudness means the volume of a sound Loudness is dependent on 2 factors:1) Amount of energy it takes to make the soundLoud sounds use a lot of energy.Soft sounds use little energy.Example: The harder a drum is hit, the more the drum will vibrate. The more an object vibrates, the louder the sound it makes.2) Distance from sound sourceThe closer the sound source, the louder the sound
13 Pitch Pitch refers to the frequency of the sound waves Sound waves with a high frequency have a high pitch(For example a soprano singer)Sound waves with a low frequency have a low pith(For example a bass singer)Soprano:Bass:
14 Difference between light and sound waves: CharacteristicsLight WavesSound WavesTypeTransverseLongitudinalMediumDoesn’t always require a medium(Can even travel through a vacuum)Requires a medium such as solid, liquid, or gas(Cannot travel through a vacuum)SpeedHigher Speed (3 x108 m/s)Lower speed (340 m/s in air)WavelengthHas a characteristic wavelengthDepends on the medium which determines the speed and frequencyFrequencyAre of different frequencies, resulting in different colorsAre of different frequencies, giving notes of different pitchesDistance TraveledCan travel through a much greater distanceDo not travel far as their energy is dissipated easily