Chapter 15 – Characteristic of Waves Learn the language of waves Learn the language of waves Wave – a disturbance that transfers energy from place to place Wave – a disturbance that transfers energy from place to place Medium – material that the wave travels in Medium – material that the wave travels in Water wave – water Water wave – water Sound wave – solid, liquid, or gas (air) Sound wave – solid, liquid, or gas (air) Mechanical waves – waves that require a medium to travel through Mechanical waves – waves that require a medium to travel through The medium does not travel along with the wave. The medium does not travel along with the wave. Water moves up and down while the wave moves past. Water moves up and down while the wave moves past.

Amplitude – height of wave Amplitude – height of wave Wavelength ( ג ) – distance between two corresponding parts of a wave (crest to crest) Wavelength ( ג ) – distance between two corresponding parts of a wave (crest to crest)

Vibration – repeated back and forth or up and down motion that can create waves. Vibration – repeated back and forth or up and down motion that can create waves. Transverse wave – a wave that has crests and troughs Transverse wave – a wave that has crests and troughs Example: a water wave Example: a water wave

Longitudinal wave – a wave that has compressions and rarefactions Longitudinal wave – a wave that has compressions and rarefactions Example: a sound wave Example: a sound wave

Frequency – is the number of waves made each second. (f = waves/sec.) Frequency – is the number of waves made each second. (f = waves/sec.) Frequency is also the number of waves that pass a given point each second. Frequency is also the number of waves that pass a given point each second. 1 wave/sec = 1 hertz (Hz) 1 wave/sec = 1 hertz (Hz) Speed = wavelength (frequency) Speed = wavelength (frequency) Speed Speed Frequency = Wavelength Wavelength Speed Speed Wavelength = Wavelength = Frequency Frequency

Example problem: The speed of a wave on a guitar string is 100 m/s and the frequency is 1,000 Hz. What is the wavelength of the wave? Example problem: The speed of a wave on a guitar string is 100 m/s and the frequency is 1,000 Hz. What is the wavelength of the wave?

Interactions of waves Reflection – waves can bounce off an object (like light off a mirror). Reflection – waves can bounce off an object (like light off a mirror). The angle of incidence – the angle between the wave and an imaginary line. The angle of incidence – the angle between the wave and an imaginary line. The angle of incidence = the angle of reflection. Mirror Light the normal

Refraction – When light moves from one medium into another it changes speed which causes it to bend. Refraction – When light moves from one medium into another it changes speed which causes it to bend. As the wave slows down it is bent towards the normal. As the wave slows down it is bent towards the normal. As the wave speeds up it is bent away from the normal. As the wave speeds up it is bent away from the normal. Light ray Air Water

Diffraction – when a wave passes a barrier or moves through a hole in a barrier it bends and spreads out. Diffraction – when a wave passes a barrier or moves through a hole in a barrier it bends and spreads out. Waves

Waves can add or cancel

Wave Interference s/interference/intrfrnc.html s/interference/intrfrnc.html s/interference/intrfrnc.html s/interference/intrfrnc.html

Constructive interference – adding of waves Constructive interference – adding of waves Destructive interference – canceling of waves Destructive interference – canceling of waves Standing waves- when a reflected wave adds to an incoming wave just right a “stationary” wave is produced. Standing waves- when a reflected wave adds to an incoming wave just right a “stationary” wave is produced. Nodes – stationary points of standing waves Nodes – stationary points of standing waves Antinodes – crests and troughs of a standing wave Antinodes – crests and troughs of a standing wave

Resonance Most objects have a natural frequency of vibration. Most objects have a natural frequency of vibration. Resonance is when the vibration passing through the object matches the object’s natural vibration. (like pushing a child on a swing. Energy input adds perfectly.) Resonance is when the vibration passing through the object matches the object’s natural vibration. (like pushing a child on a swing. Energy input adds perfectly.)