U3: What does a wave tell us? Key Concept: Change Related Concepts: Form, Patterns Global Context: Orientation in Space and Time +Constraints & adaptation “Societies manage constraints and adapt to changes by forming patterns.” In this unit you will be assessed on Criterion A and D Characteristics of Waves Table of Contents What Are Waves? Properties of Waves Interactions of Waves What are Waves? What are Waves? - Vocabulary • Wave – a disturbance involving the transfer of energy from place to place • Energy – the ability to do work. • Medium – The material through which a wave travels • Mechanical Wave – waves that require a medium • Vibration – a repeated back-and-forth or up and down motion Mechanical waves form when a source of energy causes a medium to vibrate. What are Waves? - Vocabulary • Transverse Wave – A wave that vibrates the medium at right angles, or perpendicular, to the direction in which the wave travels. • Crest – A high point in a transverse wave • Trough – A low point in a transverse wave • Longitudinal Wave – vibrates the medium in the same direction in which the wave travels • Compression – An area where the coils are close together • Rarefaction – An area where the coils are spread out WAVES A wave is a disturbance causing the transfer of energy from place to place. MOST waves (not all) need a medium to travel through. A medium can be: • Gas (for example ______ ) • Liquid (for example ______ ) • Solid (for example ______ ) What kind of waves DON’T need a medium? What Are Waves? Motion in a Transverse Wave What are the crest, trough, and rest position? What Are Waves? Motion in a Longitudinal Wave Which are the areas of compression and rarefaction in the diagram? What Are Waves? A Picture of a Sound Wave The picture shows an area of air as the compressions and rarefactions of a sound wave pass through it. The dots represent air particles. Where are the rarefaction and the compression areas? What Are Waves? Waves Transfer Energy A wave moves the bottle in a circular motion. After the wave passes, the bottle returns to where it started. How will the bottle look in the bottom picture? Properties of Waves Properties of Waves - Vocabulary • Amplitude – The maximum distance the medium vibrates from the rest position • Wavelength – The distance between two corresponding parts of a wave • Frequency – The number of waves that pass a given point in a certain amount of time • Hertz – unit of frequency; number of waves per second Properties of Waves Amplitude The amplitude of a transverse wave is the maximum distance the medium vibrates from the rest position. What are the parts of the wave? http://www.youtube.com/watch?v=OGyRe_SGnck Properties of Waves Properties of Waves All waves have amplitude, wavelength, frequency, and speed. TRANSVERSE WAVE Wavelength Crest Amplitude Rest position Trough Wavelength Direction of wave LONGITUDINAL WAVE Compression Wavelength Rarefaction Properties of Waves The table shows measurements of some properties of a sound wave in water and in air. Complete the table. Review Quiz Interactions of Waves Interactions of Waves - Vocabulary • Reflection – When a wave hits a surface, any part of the wave that cannot pass through the surface bounces back. This interaction with the surface is reflection • Refraction – The bending of waves due to the change in speed • Diffraction – When a wave moves around a barrier or passes through an opening in a barrier, it bends and spreads out. These interactions are called diffraction • Interference – The interaction between waves that meet Interactions of Waves - Vocabulary • Constructive interference – Interference in which waves combine to form a wave with a larger amplitude than any individual wave’s amplitude • Destructive interference - Interference in which waves combine to form a wave with a smaller amplitude than either original wave had. • Standing wave – A wave that appears to stand in one place, even though it is two waves interfering as they pass through each other. Interactions of Waves - Vocabulary • Node – In a standing wave, destructive interference produces points with zero amplitude, called nodes • Antinode – Points of maximum amplitude on a standing wave • Resonance – An increase in amplitude of a vibration that occurs when external vibrations match an object’s natural frequency Interactions of Waves The Law of Reflection The law of reflection states that the angle of incidence equals the angle of reflection. Interactions of Waves Constructive Interference When waves combine to form a wave with a larger amplitude, it is called constructive interference. Interactions of Waves Destructive Interference Describe the steps of destructive interference. Interactions of Waves Standing Waves As the frequency of the standing wave increases, more nodes and antinodes are created. Identify the nodes and antinodes.
