Sound waves

• Sound is caused by the vibration of particles but not all vibrations can be heard as sound.
• Common ideas about sound come from the limited range of vibrations that human ears can detect.
• Sound waves are longitudinal waves that cause particles to vibrate parallel to the direction of wave travel.
• The vibrations of sound waves can travel through solids, liquids or gases.
• The speed of sound depends on the medium through which it is travelling.
• When travelling through air, the speed of sound is about 330 metres per second (m/s).
• Sound cannot travel through a vacuum because there are no particles to carry the vibrations.
• The human ear detects sound.
• Sound is caused by the vibration of particles but not all vibrations can be heard as sound.
• Sound waves enter the ear canal and cause the eardrum to vibrate.
• Common ideas about sound come from the limited range of vibrations that human ears can detect.
• Three small bones transmit these vibrations to the cochlea.
• This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.
• Ultrasound waves have a frequency higher than the upper limit for human hearing - above 20,000 Hertz (Hz).
• The frequency of a sound wave is related to the pitch that is heard: high frequency sound waves are high pitched, low frequency sound waves are low pitched.
• Different species of animal have different hearing ranges, which explains why a dog can hear the ultrasound produced by a dog whistle but humans cannot.
• The amplitude of a sound wave is related to the volume of the sound: high amplitude sound waves are loud, low amplitude sound waves are quiet.
• Uses of ultrasound include breaking kidney stones and cleaning jewellery, where the vibrations caused by the ultrasound shake apart the dirt or kidney stones, breaking them up.
• An oscilloscope is a device used to record signals that change regularly, such as sound or other vibrations.
• The cochlea is only stimulated by a limited range of frequencies, meaning humans can only hear certain frequencies.
• Ultrasound imaging creates a picture of something that cannot be seen directly, such as an unborn baby in the womb, or faults and defects inside manufactured parts.
• Echo sounding uses high frequency sound waves to detect objects in deep water and to measure water depth.
• The range of normal human hearing is 20 Hertz (Hz) to 20,000 Hertz (20 kHz).
• The time between a pulse of sound being transmitted and detected and the speed of sound in water can be used to calculate the distance of the reflecting surface or object.
• Seismic waves are used in earthquake prediction and to map the Earth's interior.
• Sound is caused by the vibration of particles but not all vibrations can be heard as sound.
• Common ideas about sound come from the limited range of vibrations that human ears can detect.
• Seismic waves are produced by earthquakes in the Earth’s crust and can cause damage to structures on the Earth’s surface, as well as tsunamis.
• A tsunami is a large destructive wave caused by earthquakes, volcanic activity or landslides under water.
• S-waves are not detected on the opposite side of the Earth, suggesting that the mantle has solid properties, but the outer core is a fluid layer that sits above the solid inner core.
• P-waves are detected on the opposite side of the Earth.
• There are two types of seismic waves: P-waves, which are longitudinal waves, and S-waves, which are transverse waves.
• The size and positions of these shadow zones indicate there is a solid inner core.
• P-waves are faster than S-waves and can travel through both solids and liquids.
• Refractions between layers cause two shadow zones where no P-waves are detected.
• P-waves are refracted as they travel through the Earth.
• P-waves and S-waves have different properties.