Bell Work: Goal Setting • Locate your goal sheet from January. • Pick up a new goal sheet by the basket. • Fill in your area averages on the goal sheet from the orange sheet. • Fill out the rest of the goal sheet. Remember to choose specific and realistic things to do to improve your grade. Ex: Do review sheet as a practice test; review bell work 2x a week; study with a partner for 30 minutes; answer all lab questions; turn in on time
Waves carry energy from one place to another • Waves temporarily disrupt the medium through which they travel
Energy is transmitted (moved) – matter is NOT transmitted • Two categories: mechanical and electromagnetic
Electromagnetic Waves • do not need matter • perpendicular electric and magnetic fields • Radio, microwave, infrared (heat), visible light, ultraviolet, x-ray, gamma ray
Mechanical Waves • need matter to travel • Cannot travel through a vacuum
Longitudinal Waves • AKA compressional waves • matter vibrates same direction as the wave moves (parallel) • Examples: Sound is created from vibrating objects; AC current
Transverse Waves • matter moves at a right angle to the movement of energy (perpendicular) • Examples: guitar string, stadium waves • video Practice
Surface Waves • Surface wave: mixture of both Longitudinal and Transverse; matter travels in circles • Example: water waves
Wave Speed • SPEED DEPENDS ONLY ON THE MEDIUM • Medium is the stuff that the wave travels through – spring, space, air, iron, 55o F water, etc.
Wave Speed • Sound waves move at 343 m/s in room temperature air, faster in liquids and solids • Electromagnetic waves travel at speed of light c = 3 x 108 m/s; slower through matter
Transverse WaveAnatomy crest crest amplitude Matter moves wavelength Rest line Energy moves trough λ trough Practice
Bell Work: Which wave? • Which wave has the. . . • 1. . . most energy? • . . smallest • wavelength? • . . . . . smallest • frequency? • 4. . . . . smallest amplitude? • Which two waves have the same. . . .5. . . . . .amplitude? • 6. . . . . wavelength? A B C D
Wave Properties Measuring Wave Properties
Wave Relationships • as wavelength increases, frequency decreases (inversely related) • As wavelength increases, period increases (directly related) • As frequency increases, period decreases (inversely related) • Speed only depends on the medium that a wave travels through • Energy is shown in the amplitude
If a water wave oscillated up and down three times each second and the distance between wave crest is 2 m, what is its frequency? Answer: 3 Hz What is its period? Answer: 1/3 second What is its wavelength? Answer: 2 m What is its wave speed? Answer: 6 m/s
Shock Wave http://observe.phy.sfasu.edu/courses/phy101/lectures101/
Sonic Booms • http://www.physics.sfasu.edu/astro/courses/phy101/SonicBoom.html
What determines the speed of a wave? (a) the frequency (b) the wavelength (c) the amplitude (d) the period (e) the medium of transmission
What dictates the frequency of a sound wave? (a) wavelength (b) medium (c) source of the sound (d) speed (e) amplitude
Examples of Resonance • mass on a spring at resonance • swinging your legs in a swing • breaking a wine glass using sound • a singing rod caused by forced vibration • fog horn • a tuning fork exciting a guitar string • In 1940, the Tacoma Narrows Bridge was destroyed by wind-generated resonance.
Tacoma Narrows Bridge Resonance allows energy to be transferred to a vibrating object efficiently if the energy is delivered at the natural frequency of vibration.