مدرسة برديس التجريبية لغات


    WAVE MOTION

    شاطر

    omnia2010
    عضو
    عضو

    عدد المساهمات : 47
    نقاط : 31567
    تاريخ التسجيل : 04/04/2010

    WAVE MOTION

    مُساهمة من طرف omnia2010 في السبت أبريل 10, 2010 2:07 pm

    A wave is a distortion in a material or medium, where the individual parts of the material only show periodic motion, but the waveform itself moves through the material. All waves have similar characteristics, and since all forms of wave motion follow the same laws and principles, knowing the fundamentals of wave motion is important in understanding sound, light, and other types of waves.

    Questions you may have include:

    Exactly, what is wave motion?
    What are some examples of different types of waves?
    What common characteristics do all waves have?
    This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

    Useful tools: Metric-English Conversion | Scientific Calculator.

    Note: Click the Play button to hear the text being read.



    Time = 6 min. 13 sec.

    Definition of wave motion
    Wave motion is defined as the movement of a distortion of a material or medium, where the individual parts or elements of the material only move back-and-forth, up-and-down, or in a cyclical pattern.

    It appears as if something is actually moving along the material, but in reality it is just the distortion moving, where one part influences the next.

    This sounds somewhat abstract, but it can be visualized with examples.

    Examples of waves
    The following examples shows common transverse, compression and circular waveforms.

    Transverse waves
    Up-and-down motion creates transverse waves

    Wave in ballgame
    At the ballgame, someone in the stands may start up a "wave" by standing up and then sitting down. The people on one side then stand up and sit down, then the next people, and so one.

    Everyone is still in their seats, but the wave traveled through the ballpark from one end to the other.

    Rope or string
    You can shake a rope, causing a wave motion. The parts of the rope only move up-and-down, but the wave moves from one end of the rope to the other. A guitar string also has this type of motion.



    Vibrating string demonstrates waveform

    Light waves
    Light or electromagnetic waves are caused by a up-and-down motion of electric and magnetic fields, thus making them transverse waves.

    Compression waves
    Back-and-forth motion creates compression or longitudinal waves.



    Comparison of compression wave and transverse wave

    Slinky
    You can stretch out a Slinky along the floor and give one end a back-and-forth shove. The compression will move along the Slinky to its other end.

    Sound waves
    A loudspeaker cone moves back-and-forth to create a sound, which is a compression wave.

    AC electricity
    Electrons move back-and-forth in a wire, sending a wave of electric power through the wire. The electrons stay in their general region in AC electricity, while the flow through and out the wire in DC electricity.

    Circular wave
    There are cases where the material moves in a combination of transverse and compression, moving in a circular or elliptical pattern.

    Water waves
    Drop a stone in a pool and waves move outward. The surface of the water looks like it goes up and down, but actually the water molecules move in a circular or oval motion the form the wave.

    Light waves
    Although light is classified as a transverse wave, the motion of the electrical and magnetic fields may be circular instead. It is hard to tell.

    Characteristics of waves
    The characteristics of a waveform are wavelength, amplitude, velocity, and frequency. All periodic waveforms have these common characteristics.

    There are special cases, where only one crest of the wave is seen, like the the wave at a ballgame or the sound caused by an impact or explosion. In those cases, there is still a wavelength, but there is no frequency, since the waveform is not periodic.

    Wavelength
    Wavelength is defined as the distance from one crest (or maximum of the wave) to the next crest or maximum.



    Waveform showing wavelength and amplitude

    The wavelength of an ocean wave is typically several meters. The wavelength of the electromagnetic wave used in a microwave oven is in the order of a centimeter.

    Amplitude
    The height of the wave is called its amplitude. Some areas consider the middle of the wave to its peak as the amplitude, while others consider peak-to-peak as the amplitude.

    Amplitude relates to loudness in sound and brightness in light.

    Velocity
    The velocity of the wave is the measurement of how fast a crest is moving from a fixed point. For example, the velocity of water waves can be measured as their speed in a given direction with respect to the land.

    The speed of sound is about 1000 feet/second. The speed of light is 186,000 miles/second.

    Frequency
    The frequency of waves is the rate the crests or peaks pass a given point. Frequency is the velocity divided by the wavelength designated as cycles (or peaks) per second. Cycles per second is also called Hertz.

    Frequency = Velocity / Wavelength

    Another way of writing that is:

    Velocity = Wavelength x Frequency


    --------------------------------------------------------------------------------

    Tip: A way to help remember equations is to look at their units of measurement. If Velocity is in meters/second, Wavelength is in meters and Frequency is in cycles/second, then the units of the equation would be:

    meters/second = meters x cycles/second


    --------------------------------------------------------------------------------

    The frequency is also the reciprocal of the time between crests passing a point or the period of the vibration. With this measurement:

    F = 1/T

    Summary
    Waves are distortions in a material that may be transverse, compression or a combination of those movements. Light, sound and AC electric waves are important waveforms. The characteristics of a waveform are wavelength, amplitude, velocity, and frequency.
    avatar
    payoumy
    عضو فعال
    عضو فعال

    عدد المساهمات : 175
    نقاط : 35151
    تاريخ التسجيل : 21/04/2009

    رد: WAVE MOTION

    مُساهمة من طرف payoumy في الأربعاء أبريل 21, 2010 1:03 am

    Thanx omnia

      الوقت/التاريخ الآن هو الأربعاء نوفمبر 14, 2018 12:34 am