Properties of periodic waves. Next lesson. Current timeTotal duration Google Classroom Facebook Twitter. Video transcript Let's say I've got a rope. That's my rope. And what I'm going to do is, I'm going to take the left end of the rope, and I'm going to jerk it up, and then back down. And we're going to talk about what happens or what possibly gets formed. So if I take it up over here, it's going to, obviously, take the string to the right of it up with it. And the string is going to look something like this.
It's going to look something like that. Now I'm going to immediately jerk it back down. And as it passes, let's see what the rope will look like when the left-hand point is at its original position again.
So the left-hand point-- I've pulled it back down. But in the last time period, this part of the rope had some type of an upward velocity. You could imagine that way. And even after that point, even though this left-hand point starts getting pulled down, this point right here still has some upward momentum.
So it's still going to keep moving up, maybe at a slower pace because it's starting to be tugged down by the rope on its left. So it's going to look something like that. And it's going to bring the rope to its right with it. So the rope will look something like this. The rope might look something like that. And then I'm going to take this guy-- this was just an intermediate position on the way to being pulled all the way down here. So what's the rope going to look like now? This guy, he had some momentum that got him there.
But then all of that velocity will essentially go to zero because he's being tugged by the rope to the left. And now, he's going to switch directions. And he will have gotten here, at that point. The point on the line that was here-- on the purple period of time-- it had some upward momentum. So it's just going to keep going, on maybe a slower pace. It'll be there and it will bring the rest of the rope to the right of it with it.
So now my rope is going to look something like this. And then finally, where I'm going to jerk the rope back to its original position-- so this left-hand point is going to be there.
This guy, in the previous time period, was moving down rapidly. So he might get there ready to switch directions again. This guy will start moving down. This guy, right here, he had some upward momentum. So he's going to be up in this position now. And he's going to be ready to switch directions. So finally, when I've done this whole cycle, when I've moved up, down and back there again, my rope might look exactly like this.
And I could let go of the rope. I could just leave this little left point right there. And this the lump is going to propagate along the rope. Because in the next moment of time, what's it going to look like? This guy is going to be pulled up by this left-hand point. So he'll go back to his resting position. This guy's being pulled down right here by the part of the rope to the left of him, so he's going to be pulled down.
This guy's being pulled down. But this guy had some upward momentum in the time period before, so he will have moved up. And so, the very next time period, my rope is going to look something like this. And this disturbance in the rope, if I do nothing else, and if I don't lose energy to heat and friction and all that, it'll just continue moving down the rope.
If I look at the rope at some future period in time, maybe not that far down, the rope will look something like this. And if I were to keep watching it, I'll see this disturbance.
I keep using the word disturbance, because there's really no better word to use for it. I'll see this disturbance or perturbation, or whatever you want to call it, moving along the rope. When we think about what a wave is, we essentially-- I kind of jumped the gun-- I keep calling this is a disturbance, because I didn't want to use the word, wave.
Waves are defined by its frequency, wavelength, and amplitude among others. They also have two kinds of velocity: phase and group velocity. Waves have certain characteristic properties which are observable at first notice. The first property to note is the amplitude. The amplitude is half of the distance measured from crest to trough. We also observe the wavelength, which is the spatial period of the wave e.
The frequency of a wave is the number of cycles per unit time — one can think of it as the number of crests which pass a fixed point per unit time.
Mathematically, we make the observation that,. Frequencies of different sine waves. Conversely we say that the purple wave has a high frequency. Note that time increases along the horizontal. In fact,. This is the velocity at which the phase of any one frequency component of the wave travels.
For such a component, any given phase of the wave for example, the crest will appear to travel at the phase velocity. Fig 2 : This shows a wave with the group velocity and phase velocity going in different directions. The group velocity is positive and the phase velocity is negative. Energy transportion is essential to waves. It is a common misconception that waves move mass. Waves carry energy along an axis defined to be the direction of propagation.
One easy example is to imagine that you are standing in the surf and you are hit by a significantly large wave, and once you are hit you are displaced unless you hold firmly to your ground!
In this sense the wave has done work it applied a force over a distance. Since work is done over time, the energy carried by a wave can be used to generate power. Water Wave : Waves that are more massive or have a greater velocity transport more energy. Similarly we find that electromagnetic waves carry energy. Electromagnetic radiation EMR carries energy—sometimes called radiant energy—through space continuously away from the source this is not true of the near-field part of the EM field.
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. EMR also carries both momentum and angular momentum. These properties may all be imparted to matter with which it interacts through work. EMR is produced from other types of energy when created, and it is converted to other types of energy when it is destroyed.
The quantum nature of light becomes more apparent at high frequencies or high photon energy. Such photons behave more like particles than lower-frequency photons do.
Electromagnetic Wave : Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D diagram shows a plane linearly polarized wave propagating from left to right.
EM waves with higher frequencies carry more energy. This is a direct result of the equations above. If velocity is increased then we have greater momentum which implies a greater force it gets a little bit tricky when we talk about particles moving close to the speed of light, but this observation holds in the classical sense.
Again, this is an easy phenomenon to experience empirically; just stand in front of a faster wave and feel the difference! Privacy Policy. Skip to main content. Waves and Vibrations. Search for:. Waves Wave motion transfers energy from one point to another, usually without permanent displacement of the particles of the medium.
Learning Objectives Describe process of energy and mass transfer during wave motion. Key Takeaways Key Points A wave can be thought of as a disturbance or oscillation that travels through space-time, accompanied by a transfer of energy. The direction a wave propagates is perpendicular to the direction it oscillates for transverse waves.
A wave does not move mass in the direction of propagation; it transfers energy. Key Terms medium : The material or empty space through which signals, waves or forces pass. Learning Objectives Describe properties of the transverse wave.
Key Takeaways Key Points Transverse waves oscillate in the z-y plane but travel along the x axis. The direction of energy transfer is perpendicular to the motion of the wave. Longitudinal Waves Longitudinal waves, sometimes called compression waves, oscillate in the direction of propagation. Learning Objectives Give properties and provide examples of the longitudinal wave.
Key Takeaways Key Points While longitudinal waves oscillate in the direction of propagation, they do not displace mass since the oscillations are small and involve an equilibrium position. Longitudinal waves can be conceptualized as pressure waves characterized by compression and rarefaction. Key Terms rarefaction : a reduction in the density of a material, especially that of a fluid Longitudinal : Running in the direction of the long axis of a body.
Water Waves Water waves can be commonly observed in daily life, and comprise both transverse and longitudinal wave motion. Actual ocean waves are more complicated than the idealized model of the simple transverse wave with a perfect sinusoidal shape. Ocean waves are examples of orbital progressive waves , where water particles at the surface follow a circular path from the crest to the trough of the passing wave, then cycle back again to their original position.
This cycle repeats with each passing wave. As waves reach shore, the water depth decreases and the energy of the wave is compressed into a smaller volume. This creates higher waves—an effect known as shoaling. Since the water particles along the surface move from the crest to the trough, surfers hitch a ride on the cascading water, gliding along the surface. If ocean waves work exactly like the idealized transverse waves, surfing would be much less exciting as it would simply involve standing on a board that bobs up and down in place, just like the seagull in the previous figure.
If students are struggling with a specific objective, these questions will help identify such objective and direct them to the relevant content. What are the categories of mechanical waves based on the type of motion?
In which direction do the particles of the medium oscillate in a transverse wave? As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Changes were made to the original material, including updates to art, structure, and other content updates.
Skip to Content Go to accessibility page. Physics My highlights. Table of contents. Chapter Review. Test Prep. By the end of this section, you will be able to do the following: Define mechanical waves and medium, and relate the two Distinguish a pulse wave from a periodic wave Distinguish a longitudinal wave from a transverse wave and give examples of such waves.
Teacher Support The learning objectives in this section will help your students master the following standards: 7 Science concepts. The student knows the characteristics and behavior of waves. The student is expected to: A examine and describe oscillatory motion and wave propagation in various types of media.
Teacher Support Many people think that water waves push water from one direction to another. Teacher Support [BL] Any kind of wave, whether mechanical or nonmechanical, or transverse or longitudinal, can be in the form of a pulse wave or a periodic wave. Teacher Support Transverse and longitudinal waves may be demonstrated in the class using a spring or a toy spring, as shown in the figures.
However, the sound wave coming out of a speaker rattles a sheet of paper in a direction that shows that such sound wave is longitudinal. Teacher Support Energy propagates differently in transverse and longitudinal waves.
Introduction to Waves This video explains wave propagation in terms of momentum using an example of a wave moving along a rope. Click to view content. Watch Physics: Introduction to Waves. This video is an introduction to transverse and longitudinal waves.
In a longitudinal sound wave, after a compression wave moves through a region, the density of molecules briefly decreases. Why is this?
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