Wave’s Up, Dude

Waves – Lesson 1 – The Nature of a Wave
From Physics Classroom

Categories of Waves

Waves come in many shapes and forms. While all waves share some basic characteristic properties and behaviors, some waves can be distinguished from others based on some observable (and some non-observable) characteristics. It is common to categorize waves based on these distinguishing characteristics.

Longitudinal versus Transverse Waves versus Surface Waves

One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction that the waves travel. Categorizing waves on this basis leads to three notable categories: transverse waves, longitudinal waves, and surface waves.

A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves. Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil up and down. Energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. In this case, the particles of the medium move perpendicular to the direction that the pulse moves. This type of wave is a transverse wave. Transverse waves are always characterized by particle motion being perpendicular to wave motion.

A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves. Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil left and right. Energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced leftwards and rightwards. In this case, the particles of the medium move parallel to the direction that the pulse moves. This type of wave is a longitudinal wave. Longitudinal waves are always characterized by particle motion being parallel to wave motion.

A sound wave traveling through air is a classic example of a longitudinal wave. As a sound wave moves from the lips of a speaker to the ear of a listener, particles of air vibrate back and forth in the same direction and the opposite direction of energy transport. Each individual particle pushes on its neighboring particle so as to push it forward. The collision of particle #1 with its neighbor serves to restore particle #1 to its original position and displace particle #2 in a forward direction. This back and forth motion of particles in the direction of energy transport creates regions within the medium where the particles are pressed together and other regions where the particles are spread apart. Longitudinal waves can always be quickly identified by the presence of such regions. This process continues along the chain of particles until the sound wave reaches the ear of the listener.

Waves traveling through a solid medium can be either transverse waves or longitudinal waves. Yet waves traveling through the bulk of a fluid (such as a liquid or a gas) are always longitudinal waves. Transverse waves require a relatively rigid medium in order to transmit their energy. As one particle begins to move it must be able to exert a pull on its nearest neighbor. If the medium is not rigid as is the case with fluids, the particles will slide past each other. This sliding action that is characteristic of liquids and gases prevents one particle from displacing its neighbor in a direction perpendicular to the energy transport. It is for this reason that only longitudinal waves are observed moving through the bulk of liquids such as our oceans.

Earthquakes are capable of producing both transverse and longitudinal waves that travel through the solid structures of the Earth. When seismologists began to study earthquake waves they noticed that only longitudinal waves were capable of traveling through the core of the Earth. For this reason, geologists believe that the Earth’s core consists of a liquid – most likely molten iron.

While waves that travel within the depths of the ocean are longitudinal waves, the waves that travel along the surface of the oceans are referred to as surface waves. A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are neither longitudinal nor transverse. In longitudinal and transverse waves, all the particles in the entire bulk of the medium move in a parallel and a perpendicular direction (respectively) relative to the direction of energy transport. In a surface wave, it is only the particles at the surface of the medium that undergo the circular motion. The motion of particles tends to decrease as one proceeds further from the surface.

Any wave moving through a medium has a source. Somewhere along the medium, there was an initial displacement of one of the particles. For a slinky wave, it is usually the first coil that becomes displaced by the hand of a person. For a sound wave, it is usually the vibration of the vocal chords or a guitar string that sets the first particle of air in vibrational motion. At the location where the wave is introduced into the medium, the particles that are displaced from their equilibrium position always moves in the same direction as the source of the vibration. So if you wish to create a transverse wave in a slinky, then the first coil of the slinky must be displaced in a direction perpendicular to the entire slinky. Similarly, if you wish to create a longitudinal wave in a slinky, then the first coil of the slinky must be displaced in a direction parallel to the entire slinky.

Electromagnetic versus Mechanical Waves

Another way to categorize waves is on the basis of their ability or inability to transmit energy through a vacuum (i.e., empty space). Categorizing waves on this basis leads to two notable categories: electromagnetic waves and mechanical waves.

An electromagnetic wave is a wave that is capable of transmitting its energy through a vacuum (i.e., empty space). Electromagnetic waves are produced by the vibration of charged particles. Electromagnetic waves that are produced on the sun subsequently travel to Earth through the vacuum of outer space. Were it not for the ability of electromagnetic waves to travel to through a vacuum, there would undoubtedly be no life on Earth. All light waves are examples of electromagnetic waves. Light waves are the topic of another unit at The Physics Classroom Tutorial.

A mechanical wave is a wave that is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another. A sound wave is an example of a mechanical wave. Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and jump rope waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a jump rope wave requires a jump rope.

The above categories represent just a few of the ways in which physicists categorize waves in order to compare and contrast their behaviors and characteristic properties. This listing of categories is not exhaustive; there are other categories as well. The five categories of waves listed here will be used periodically throughout this unit on waves as well as the units on sound and light.

Investigate!

Earthquakes and other geologic disturbances sometimes result in the formation of seismic waves. Seismic waves are waves of energy that are transported through the earth and over its surface by means of both transverse and longitudinal waves.

Source: http://www.physicsclassroom.com/class/waves/Lesson-1/Categories-of-Waves

 

 

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10 thoughts on “Wave’s Up, Dude

  1. At Dream State October 1, 2016 at 5:54 pm Reply

    It would be funny if they had not been serious. Telling you to come earlier as if you are their servant. Time to send them the bill. If only they knew how much you were able to do in those 40 minutes. A couple of stupid remarks got you to remove a huge file off your desk! Ha. And to think you did not want to go. Only humored me so I could deal with a distorted message. Yeah, fun is not a factor in it at all. You can get back to what you prefer, but I now have to sort out some nasty business.

  2. thesevenminds October 2, 2016 at 6:18 pm Reply

    That was hard work. (After I was denied special access to the telescope.😀 ) It was far from a waste of time. But after a long day, which started when the kids were still asleep, I was not going to listen to a few kids telling me to come early as if they were paying me to. Besides, too busy getting my picture taken elsewhere.

  3. thesevenminds October 2, 2016 at 6:21 pm Reply

    I was going to write off the dude as the intruder, and I still lean towards it. But there was much intrusion at his stand. Seemed like a swipe. See what you can make of it.

  4. At Dream State October 6, 2016 at 7:36 pm Reply

    WHOA))) Either you guessed the nobel prizes and set agenda right, or your hidden ‘friends’ showed to be more important than your hiding enemies. People complaining? They near spelled out the set agenda! The next page showing that they understand full well. And even though the kids chose to play dumb, they will be kept around to mess with the light some more. One of them has his own room after all. *wink*

  5. At Dream State October 6, 2016 at 7:54 pm Reply

    You complained about it the first time already. If you think about what it reminds you of, it should come with its own answers. You saw movement behind them. That is the link. Past into present, even though they like to do things the other way.

    I see 2 + 2. The middle is not for you.
    Flour sack. Particles put you on track.
    Kemistry and math. You know the path.
    0 + 0 shows repeat. Reclaim your seat.

    Something about that “repeat” shows to have another layer, so it needs to be looked at again. Just not now.

  6. thesevenminds October 7, 2016 at 4:03 pm Reply

    “Hidden friends”. Right. You know I fly HannaH Solo. (Sola sounds off as olo is the void. Never mind. Those with the in-eyes to read, will know what it means.) Frenemies have their own agendas. I simply cut through the prop to find it. Nonsense pushed me to go back to theoretical basics to remove the obvious metaphysics, then rebuild from there. Yes, physicists use formulas and fancy toys, but if they cannot show applied physics they will find themselves cut off like many other scientists. Or not even know it already happened. Then again, some do not need a milli to continue their play. *wink* 44 minutes and look what happens.
    At the time I did not know why I said molecule instead of atom. It was the O7 that threw me off. That would be a molecule in itself, but an agent to protect or conduce the artificial metal? And why does it not mather? Should be a good point for a restart. I forgot my other point. You are not the only one who is tired.

  7. thesevenminds October 7, 2016 at 4:19 pm Reply

    No go, wackalot mc. You are on point. It was much needed, so on point it remains. I struggled to relate the two. I noticed the other tension spot as I stood and watched their strange behaviors. Pick up on the hints buried in it, yet find the mistake I was about to make. Wise up to side step it. Phew. Just in time for some math. Full circle. Well, two paraboles. Parables. And more nanoparticles in the end. Whose magic? Topic closed.

  8. At Dream State October 8, 2016 at 10:34 am Reply

    Um, “wackalot” is not a term you want to use now that you got nobel friends and all…

  9. thesevenminds October 8, 2016 at 3:34 pm Reply

    😀 😀 I was not thinking tantra. Yet. *wink*

  10. At Dream State October 12, 2016 at 11:54 am Reply

    Told you not to use it. Nice ‘friends’ you got. 😐

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