What are waves? Wave Definition: A disturbance that transfers energy from place to place. What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid. What causes waves? Waves are created when a source of energy causes a medium to vibrate. A vibration is a repeated back and forth or up and down motion. Types of waves: Waves are classified according to how they move. Transverse wave Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave. Transverse means across.The highest parts are called crests the lowest parts are called troughs. Longitudinal Wave Matter vibrates in the same direction as the wave travels. Example: Slinky Longitudinal wave The parts,where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions. Properties of Waves Basic Properties of Waves Amplitude Wavelength Frequency Speed Draw Transverse wave and label: crest & trough the old Slinky song) Amplitude of transverse waves The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. You can find the amplitude of a transverse wave by measuring the distance from rest position to crest or rest position to trough. The greater the amplitude the greater the greater the energy the wave has. Wavelength of Transverse wave The distance between crest to crest or trough to trough. Amplitude of a longitudinal wave. The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes. Frequency The number of complete waves that pass a given point in a certain amount of time. Frequency measured in hertz (Hz). The shorter the wavelength the higher the frequency Frequency and energy: The higher the frequency the more energy the wave has. Speed The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula. Speed = wavelength x frequency Frequency = speed/wavelength Wavelength = speed/frequency Speed Waves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant. Ways Waves Interact Reflection Refraction Diffraction Interference Constructive Destructive Absorption and scattering Reflection When an object or wave hits a surface through which it cannot pass, it bounces back. Angle of incidence: The angle made by the beam of light traveling toward the mirror Angle of reflection: The angle made by the beam of light reflecting from the mirror. Law of reflection The angle of incidence=the angle of reflection Examples of reflection Mirror Echo Ball against a wall Refraction is when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which causes it to bend. The bending of waves due to a change in speed is called refraction. Refraction Diffraction When a wave passes a barrier or moves through a hole in a barrier it bends and spreads out. Interference Constructive interference occurs whenever two waves combine to make a wave with a larger amplitude. Destructive interference when the amplitudes of two waves combine producing a smaller amplitude. Absorption Some of the light energy gets absorbed before it is reflected back Example: when you shine a flash light in the air, the air particles absorb some of the energy from the light and that caused the light to become dim Scattering of light It is like the scattering of light beam when it comes out of the sun Not all waves require a medium to travel. Light from the sun travels through empty space. Mirrors Plane mirror: your picture in the mirror is reversed. Lenses Convex lense Convex lense Longitudinal waves Draw a Compressional wave: label compression& rarefaction Resonance Most objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency. An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.
