A moving ridge is a disturbance that moves along a medium from i end to the other. If i watches an sea wave moving along the medium (the ocean water), ane can observe that the crest of the wave is moving from ane location to another over a given interval of fourth dimension. The crest is observed to comprehend distance. The speed of an object refers to how fast an object is moving and is ordinarily expressed as the distance traveled per time of travel. In the case of a moving ridge, the speed is the distance traveled by a given indicate on the moving ridge (such as a crest) in a given interval of time. In equation course,
If the crest of an body of water wave moves a altitude of twenty meters in x seconds, and then the speed of the body of water wave is 2.0 m/s. On the other manus, if the crest of an ocean wave moves a distance of 25 meters in 10 seconds (the aforementioned corporeality of fourth dimension), so the speed of this ocean moving ridge is ii.5 1000/due south. The faster wave travels a greater distance in the same corporeality of time.
Sometimes a moving ridge encounters the end of a medium and the presence of a different medium. For example, a wave introduced by a person into ane end of a slinky volition travel through the slinky and eventually reach the end of the slinky and the presence of the hand of a 2d person. Ane behavior that waves undergo at the stop of a medium is reflection. The wave will reflect or bounce off the person's mitt. When a wave undergoes reflection, it remains within the medium and merely reverses its direction of travel. In the instance of a slinky moving ridge, the disturbance can be seen traveling back to the original finish. A slinky wave that travels to the end of a slinky and dorsum has doubled its distance. That is, by reflecting dorsum to the original location, the moving ridge has traveled a distance that is equal to twice the length of the slinky.
Reflection phenomena are unremarkably observed with audio waves. When you permit out a holler within a canyon, you often hear the echo of the holler. The sound wave travels through the medium (air in this case), reflects off the coulee wall and returns to its origin (you). The result is that y'all hear the echo (the reflected sound moving ridge) of your holler. A classic physics problem goes like this:
Noah stands 170 meters away from a steep canyon wall. He shouts and hears the repeat of his voice i 2d later. What is the speed of the moving ridge?
In this case, the sound wave travels 340 meters in 1 second, and then the speed of the wave is 340 thousand/s. Remember, when in that location is a reflection, the moving ridge doubles its distance. In other words, the distance traveled by the audio moving ridge in 1 second is equivalent to the 170 meters down to the coulee wall plus the 170 meters dorsum from the canyon wall.
Variables Affecting Wave Speed
What variables affect the speed at which a wave travels through a medium? Does the frequency or wavelength of the wave affect its speed? Does the amplitude of the wave touch its speed? Or are other variables such as the mass density of the medium or the elasticity of the medium responsible for affecting the speed of the wave? These questions are often investigated in the form of a lab in a physics classroom.
Suppose a wave generator is used to produce several waves inside a rope of a measurable tension. The wavelength, frequency and speed are determined. Then the frequency of vibration of the generator is inverse to investigate the effect of frequency upon wave speed. Finally, the tension of the rope is altered to investigate the consequence of tension upon wave speed. Sample data for the experiment are shown below.
Speed of a Wave Lab - Sample Information
| Trial | Tension
(N) | Frequency
(Hz) | Wavelength
(m) | Speed
(one thousand/s) |
| 1 | 2.0 | 4.05 | 4.00 | 16.2 |
| 2 | ii.0 | viii.03 | 2.00 | xvi.1 |
| 3 | 2.0 | 12.30 | 1.33 | 16.4 |
| 4 | ii.0 | 16.2 | 1.00 | 16.ii |
| 5 | 2.0 | xx.ii | 0.800 | xvi.2 |
| half dozen | v.0 | 12.8 | 2.00 | 25.6 |
| 7 | 5.0 | 19.3 | ane.33 | 25.seven |
| 8 | v.0 | 25.5 | 1.00 | 25.5 |
In the first five trials, the tension of the rope was held constant and the frequency was systematically inverse. The data in rows 1-5 of the tabular array in a higher place demonstrate that a alter in the frequency of a wave does non affect the speed of the wave. The speed remained a most abiding value of approximately sixteen.ii m/s. The pocket-size variations in the values for the speed were the result of experimental error, rather than a sit-in of some physical law. The information convincingly show that wave frequency does non affect wave speed. An increase in moving ridge frequency acquired a decrease in wavelength while the wave speed remained constant.
The last three trials involved the aforementioned procedure with a different rope tension. Observe that the speed of the waves in rows 6-8 is distinctly dissimilar than the speed of the moving ridge in rows 1-5. The obvious cause of this divergence is the amending of the tension of the rope. The speed of the waves was significantly higher at college tensions. Waves travel through tighter ropes at higher speeds. Then while the frequency did non touch on the speed of the wave, the tension in the medium (the rope) did. In fact, the speed of a wave is not dependent upon (causally affected by) properties of the wave itself. Rather, the speed of the wave is dependent upon the backdrop of the medium such as the tension of the rope.
Ane theme of this unit has been that "a moving ridge is a disturbance moving through a medium." At that place are two distinct objects in this phrase - the "wave" and the "medium." The medium could be water, air, or a slinky. These media are distinguished by their backdrop - the textile they are made of and the physical properties of that textile such as the density, the temperature, the elasticity, etc. Such physical backdrop describe the material itself, not the wave. On the other manus, waves are distinguished from each other by their backdrop - amplitude, wavelength, frequency, etc. These properties describe the wave, not the material through which the moving ridge is moving. The lesson of the lab activity described above is that wave speed depends upon the medium through which the moving ridge is moving. Only an alteration in the properties of the medium volition cause a change in the speed.
Nosotros Would Similar to Suggest ...
Why simply read about it and when y'all could exist interacting with it? Interact - that's exactly what you do when yous use one of The Physics Classroom's Interactives. We would like to suggest that you lot combine the reading of this folio with the use of our Slinky Lab Interactive. Y'all can observe it in the Physics Interactives section of our website. The Slinky Lab provides the learner with a simple environment for exploring the motility of a wave along a medium and the factors that affect its speed.
Cheque Your Agreement
1. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the 2 pulses (A or B) below volition travel from the manus to the wall in the least amount of fourth dimension? Justify your answer.
2. The teacher and then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the mitt to the wall in the least amount of time ? Justify your answer.
3. The fourth dimension required for the audio waves (five = 340 m/due south) to travel from the tuning fork to point A is ____ .
| a. 0.020 2d | b. 0.059 second |
| c. 0.59 2nd | d. 2.9 2d |
4. Two waves are traveling through the same container of nitrogen gas. Moving ridge A has a wavelength of one.v one thousand. Wave B has a wavelength of 4.5 1000. The speed of wave B must exist ________ the speed of wave A.
| a. one-ninth | b. ane-third |
| c. the same as | d. three times larger than |
5. An automatic focus photographic camera is able to focus on objects by utilize of an ultrasonic sound wave. The camera sends out sound waves that reflect off distant objects and return to the photographic camera. A sensor detects the time it takes for the waves to return and then determines the altitude an object is from the camera. The camera lens then focuses at that altitude. Now that's a smart camera! In a subsequent life, you might take to exist a camera; so try this trouble for practice:
If a sound wave (speed = 340 m/s) returns to the photographic camera 0.150 seconds later leaving the camera, then how far away is the object?
vi. TRUE or False:
Doubling the frequency of a wave source doubles the speed of the waves.
seven. While hiking through a coulee, Noah Formula lets out a scream. An repeat (reflection of the scream off a nearby canyon wall) is heard 0.82 seconds after the scream. The speed of the sound wave in air is 342 m/southward. Calculate the altitude from Noah to the nearby coulee wall.
8. Mac and Tosh are resting on top of the water almost the end of the puddle when Mac creates a surface moving ridge. The wave travels the length of the pool and back in 25 seconds. The puddle is 25 meters long. Determine the speed of the wave.
ix. The water waves below are traveling along the surface of the bounding main at a speed of 2.5 m/s and splashing periodically confronting Wilbert's perch. Each adjacent crest is 5 meters apart. The crests splash Wilbert'south anxiety upon reaching his perch. How much time passes between each successive drenching? Answer and explain using consummate sentences.
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