[ul] [li]Sound cannot travel in a vacuum.[/li] [li]Sound needs a medium to travel (or propagate - or pass) through.[/li] [li]It transfers its energy through particles.[/li] [li]It is a wave that compresses and decompresses particles to traverse through them.[/li] [li]It is a longitudinal wave.[/li] [li]Higher pitch = Higher Frequency (Hz).[/li] [li]Our hearing range is 20Hz to 20kHz (20 000 Hz).[/li] [li]Under 20Hz is [b]Infrasound[/b].[/li] [li]Over 20kHz is [b]Ultrasound[/b].[/li] [li]An [b]anechoic chamber[/b] absorbs sound.[/li] [li]Sound is produced by vibrations (compression, rarefaction).[/li] [li]More displacement from the base, causes more [b]amplitude[/b], and a louder sound.[/li] [li]Louder = more energy in the wavelength[/li] [/ul] Striking a [b]tuning fork[/b] in air will not produce much sound but when a tuning fork vibrates and is placed on to a larger surface, the surface will vibrate, making the air around it to vibrate, amplifying the sound, allowing us to hear. The following example demonstrates the limitations of the propagation of sound: [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488046355/sound_propagation_zckkid.svg'] [h3]Oscilloscopes[/h3] This is an oscilloscope: [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488047274/2120C_front_lrg_tilku6.jpg'] [b]Oscilloscopes[/b] convert signals for sound, into a visualized representation of sound waves. It is connected to a signal generator of some sort. [u]Low Frequency (Low Hz) Reading[/u] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488047672/low_frequency_htja28.svg'] [u]High Frequency (High Hz) Reading[/u] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488047672/high_frequency_gqg3rr.svg'] The greater the number of waves along the oscilloscope, the higher the frequency. Because sound propagates through particles, if a material is more dense, it propagates faster. For example, in the following diagram, the person on the left is trying to hear something the person on the right says. However, the one underwater will hear it much faster (less than 2 seconds), compared to the person in air (just over 6 seconds), as water is denser than air, and can transmit sound quicker. [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488048548/sound_speed_example_cyx2ur.svg'] Therefore the speed of sound can vary. It also moves quicker in air at around 30[degree], around 350m/s. [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488048816/6794978_orig_lxknjp.png']