Waves and Wave Variables California Standards 4a Students know waves carry energy from one place to another. 4b Students know how to identify transverse and longitudinal waves in mechanical media, such as springs and ropes and on the earth (seismic waves). 4c Students know how to solve problems involving wavelength, frequency, and wave speed.

Waves in General Waves are caused by vibrations of a medium Waves transfer energy NOT matter. Waves can be more than one place at one time. More than one wave can be at the same place at the same time Examples of waves: radio signals, pulses on a rope, water waves, seismic or earthquake waves, sound and light. Wave representations Questions: What is the cause of a wave? Do waves transfer matter, energy or both? List several ways waves differ from matter. List some examples of waves. Activities: Vibrate pen on board and call it a wiggle in time (a vibration). Then move pen across board while wiggling it calling it a wiggle in time and space (a wave). Point out that every point on the wave is in vibration. Sum up by saying that a wave is caused by a vibration and is a collection of vibrations. Discuss how waves transfer only energy. Point out circular motion of buoy in water wave. Show Laser Disk video Chp. 19-24 to show motion and examples of waves. Discuss how waves differ from matter in that a wave can be more than one place at one time and more than one wave can be at the same place at one time. Describe how can receive radio waves from many stations at this spot and these stations can be heard from many locations. List other examples of waves Label sine wave representation and then draw wave front representation. Link two pictures.

Wave Variables Amplitude: Maximum displacement of vibration from equilibrium position. Wavelength: Distance between two parts of wave at same point in vibration. Distance between consecutive crests or troughs. Frequency: number of vibrations wave causes in a second Period: Time for one vibration caused by wave Wave velocity: how fast a wave spreads out Media: matter wave travels through Question: Define the following terms for waves: amplitude, wavelength, frequency, period and wave velocity. Activities: Label amplitude and wavelength on sine wave representation of a wave. Discuss how wavelength is distance between two parts of wave at same point in their vibration. Label wavelength on wave front representation of a wave. Define period and mention it is measured in seconds Define frequency and it is measured in hertz or per seconds Define media and wave velocity Transparency

Types of Waves: Longitudinal vs. Transverse Vibration of wave is in same direction as wave moves. Slinky spring compressed and released. Examples include: P seismic wave, sound waves, waves due to an explosion Vibration of wave is in perpendicular direction to wave motion. Slinky waved side to side Examples include S seismic wave, and light waves Question: Distinguish between longitudinal and transverse waves. Describe the motion of a slinky when each type of wave is produced. Give examples of both types of waves. Activities: 1) Demo transverse and longitudinal waves with slinky. 2) Show wave videos Chp. 19-24 and discuss whether transverse or longitudinal waves. 3) List examples of each type of wave 4) Transparency

Types of Waves: EM vs. Mechanical Electromagnetic (EM) waves can travel through a vacuum Caused by vibration of electric charge Move fastest through least dense media Examples include radio, x-ray, gamma, visible light and microwaves Mechanical waves require a medium to travel through. Caused by vibration of matter Move fastest through dense media Examples include seismic waves, sound, and water waves Distinguish between electromagnetic and mechanical waves. Give examples of each type of wave. Activities: Describe differences between em and mechanical waves. Show two posters and point out that the waves are formed by the vibration of different objects and produce 2 different spectrums. Point out density and speed relationships. List examples of each type of wave.

Mathematical Relationships for Waves Wave velocity = frequency x wavelength V=f l Wavelength and frequency vary inversely w/ one another Period = 1/ frequency (T=1/f) Energy is proportional to the amplitude of a wave squared (E~ A2) Twice the amplitude requires 4x the energy Question: Write the equations relating the following wave variables: a)wave velocity, frequency and wavelength b) wave period and frequency c) wave amplitude and energy. Activities Use tapping demo to come up with period and frequency relationship Use idea of finding speed of train knowing car length and frequency. Discuss meaning of squared quantity in energy equation.

Check Question What is the wavelength of a radio stations waves that travel at 300 000 000 m/s at a frequency of 100 MHz?

Uses of Waves Outer core of earth is liquid Longitudinal earthquake waves can travel through water but transverse waves cannot. Transverse wave shadow zone was detected in 1910 at distances from 11,570 to 15, 570 km away from the Earthquake’s epicenter. Meant that these waves had passed through a liquid. Same sort of wave tracing now used to find oil and other mineral resources. Question: Describe how the Earth’s outer core was found to be liquid.

Simple Harmonic Motion Requires linear restoring force D,v and a in SHM Simple pendulum T=2p (l/g)1/2 F=mg sin Q Linear for small Q Mass on spring F=-kX T= 2p (m/k)1/2