Waves; Frequency vs. Amplitude

Natural Frequency and Resonance

Conclusion

Clayton Poteet

   When you move a jump rope up and down on the ground what does it do? It creates a small “hump” that travels down the rope and eventually dies out. What if one of your friends holds the other end of the jump rope loosely and you continuously move it up and down? The humps are going to last all the way to the hand of your friend and be quite large. After, try pulling the jump rope as tight as you can and moving it up and down. What kind of hump is that going to create? Let me tell you that this will create a very small, quick hump that might not last all the way to the hands of your friend. This explanation has the same concept as our experiment. However instead of a jump rope we used a small string attached to a wiggler which sent energy through the string which caused a wave. The frequency, or amount of times the wiggler moved the small string, caused the string to have different amounts of harmonic motion. We found that frequency can cause the rope to have much more periods of harmonic motion and also it can cause the string to have less amounts of harmonic motion. The lower the frequency, the less amounts of simple harmonic motions we had. Now what about amplitude?

    Do frequency and amplitude have a relation? Absolutely they do! In this chapter we were learning about waves and their properties. Nodes, anti-nodes, period, and pulse are just some vocabulary words we learned. But what do they all mean? This lab helped us visually see the differences between nodes, anti-nodes, pulses and waves and, also, exactly what they are. Going into the experiment we knew that the frequency is going to affect the amplitude of a wave but we didn’t know if it would be positive or negative. My hypothesis was that the higher the frequency the greater the amplitude would be because the string would be moving faster, causing more disruption in the string which in turn would cause larger waves. However, we found out that was wrong. In doing the lab we found that the higher the frequency the lower the amplitude would be rather then the other way around. I believe this is so because of the amounts of simple harmonics we had involved. It all makes sense when you you think about it. The frequency is how many times the string is going to be moved in an amount of time. Since we were increasing our frequency, we were also increasing the amounts of time that string was being moved. This didn’t allow the string to fully peek like it did when the frequency was lower. Therefore, the amplitude decreased as the frequency increased.

    This lab was one of my favorites we have done in our physics class so far this year. It is very simple but it can certainly help students see anti-nodes and nodes appear right in front of their eyes! You can even have some fun with competitions to see who can create the most simple harmonics on one string. The world is full of interesting things, now it is our job to find them!