Chapter 11: Waves

Waves

Do the wave!!Intro to WavesIn class on board- w/demos Wave vs particleMechancal vs non-mechancalLongitudinal vs TransverseSpreading of waves

I. Nature of a WaveA. Definition of wave A disturbance which travels through a medium from one point in space to the others.Properties of WavesEnergy is transferred from one place to another in a wave motion.Motion of the medium (particles of the medium) is usually periodically vibratory.Only the shape or form of wave travels, not the medium.

Wave MotionA wave travels along its medium, but the individual particles just move up and down.

Wave MotionAll types of traveling waves transport energy. Study of a single wave pulse shows that it is begun with a vibration and transmitted through internal forces in the medium.

Continuous waves start with vibrations too..

Wave MotionWave characteristics : use string and glue to create a wave- include the following label and define each characteristic.

Amplitude, A Wavelength, Crest Trough Rest line

Define the following:

7 Anatomy of a Wave

Amplitude Wavelength ()Frequency (f)Period (T)Wave velocity (v) A wave is usually described by the following terms :Each term will be explained.

The amplitude is the maximum displacement of the medium from its equilibrium position(rest line). The amplitude of a wave refers to the distance from the equilibrium point (or the distance from highest to lowest point of vibration)The wavelength () is the minimum distance between two points which are in phase.The frequency () is the number of complete oscillations (waves)made in one second. The frequency of a wave refers to how many waves pass by a point in a given amount of time (usually a second) Unit : Hz The period (T) The period of a wave is the time for a to make one complete cycle. Period, being a time, is measured in units of time such as seconds, hours, days or years. It is the time taken for one complete oscillation(wave). It is related to frequency by T = 1/ Unit : s

Transverse Paper Activity Use construction paper- string -glue create a transverse wave Label partsCrest- highest part off rest of transverse waveTrough-lowest part off rest of transverse waveAmplitude-maximum displacement off restWavelength-distance between two points crest to crestFrequency- to how many waves pass by a point in a given amount of time (usually a second)the entire sheet is one secondPeriod-time for a wave to make one complete cycle.

Longitudinal wave

Graphing harmonic motion- using paper and stringWhen oscillations are small, the motion is called simple harmonic motion (shm) and can be described by a simple sine curve.See animation

Longitudinal paper activityFlip side of transverse wave model create a longitudinal wave draw slinky-like modelLabel partsCompression-Crest- particles highest densityRarefaction -Trough-particles stretchedAmplitude-maximum displacement off rest-compression to restWavelength-distance between two points compression to compressionFrequency- to how many waves pass by a point in a given amount of time (usually a second)the entire sheet is one secondPeriod-time for a wave to make one complete cycle.

1. Classification based on direction of vibrationaccording to the direction of vibration, waves are classified into : (a) Transverse wave; (b) Longitudinal waves.Types of Waves: Transverse and LongitudinalThe motion of particles in a wave can either be perpendicular to the wave direction (transverse) or parallel to it (longitudinal).

a. Transverse WavesThe waveform appears in the shape of sine curve.A wave in which the motions of the matter particles are perpendicular to the direction of propagation of the wave itself.Water waves, pulse in a stretched string,transverse wave demonstrator.

Examples

Types of Waves: LongitudinalSound waves are longitudinal waves:

Longitudinal WavesA wave in which the motions of the matter particles are in the same direction as the wave propagation.ExamplesSound, or a spring oscillating up and down

Mechanical Waves Based on medium A material medium is necessary for the transmission for mechanical waves. Mechanical waves cannot travel through vacuum.Due to forces on particles in the medium that are next to each other, the disturbance is transmitted from one layer to the next through the medium. Sound waves require a mediumMechanical waves require a medium to carry the energy ie: gas liquid solid.

air, water, metal plumbing carries sound

Non Mechanical Waves (Electromagnetic Waves)Material medium is not essential for propagation. e/m waves travel through vacuum.Disturbance of electric and magnetic fields travelling through space.All electromagnetic waves are transverse waves.X-rays, radio waves, micro-waves,etc.examples

Categories of Waves

Waves are classified into different types according to their natures :

Harmonic MotionA wave is an oscillation that travels.A ball floating on water can oscillate up and down in harmonic motion.The surface of the water oscillates in response and the oscillation spreads outward from where it started.

VibrationsVibrational MotionVibration: in a general sense, anything that switches back and forth, to and fro, side to side, in and out, off and on, loud and soft, or up and down is vibrating. A vibration is a wiggle in time.Wave: a wiggle in both space and time is a wave. A wave extends from one place to another.Vibrations and waves: the source of all waves is something that is vibrating. Waves are propagations of vibrations throughout space. Harmonic motion occurs when a vibration repeats and is converted (no energy input is needed to continue the motion) Properties of Periodic Motion

Cycle: A cycle is a unit of motion that repeats.Cpo-t and f

The Wave EquationThe wave velocity is the displacement traveled by the wave in one second ....The wave velocity (v) is related to frequency and wavelength by -- v = The Wave Equation

Using the Wave EquationExample :A travelling wave of wavelength 0.6m moves at a speed of 3.0 m/s. What is the period of this wave ?Then the period of this wave is ???Period T = 1/ T = 1/5.0 or 0.2 s = 0.6 m, v = 3.0 m/sf = ?

By using the wave equation, v = = v/ f = (3.0 m/s)/(0.6 m) = 5.0 HzThe unit of m cancel outand you are left with 5.0/s which is 5.0 HzRelationship between speed, frequency, and wavelengthThe speed of a wave equals the frequency times the wavelength.v = f lFrequency (cycles/sec)Wavelength (m)Speed (m/sec)WAVE EQUATION ACTIVITYCalculate the wave equation using graph paper model activity

Sine curve- draw 1,2,4,5,10, 20 waves each wave has an amplitude of 2 blocks to crest and 2 blocks to trough.

CALCULATE:Frequency-periodwavelength Wave speed

1What is the wave speed if the period of a wave is 4 seconds and the wavelength is 1.8 m?7.2 m/sBAnswer2A fisherman noticed that a float makes 30 oscillations in 15 seconds. The distance between to consecutive crests is 2 m. What is the wave speed?4 m/sBAnswer3What is the wavelength of a wave trveling with a speed of 6 m/s and a period of 3s?18 m/sBAnswer

A.Reflection- The bouncing back of a wave when it meets a surface or boundaryi. Echo- is a reflection of sound wavesB.Diffraction bending of a wave around an object I. Sound waves around a doorAM waves are longer and travel around a buildingFM waves are shorter and cant move aroundE. Refraction bending of a wave as it passes from one medium to anotheri. waves travel at different speeds when passing through different mediumsDemo pencil in a beaker light travels faster in air than water

Constructive interference happens when waves add up to make a larger amplitude.Suppose you make two wave pulses on a stretched string. One comes from the left and the other comes from the right. When the waves meet, they combine to make a single large pulse.

What happens when one pulse is on top of the string and the other is on the bottom? When the pulses meet in the middle, they cancel each other out.During destructive interference, waves add up to make a wave with smaller or zero amplitude.

SLINKY LAB