When studying physics, one of the fundamental concepts that you’ll come across is resonance. The term refers to a phenomenon where a system vibrates at the same frequency as an external force. One of the most famous examples of resonance that students are taught is the collapse of the Tacoma Narrows Bridge. However, a closer look at this incident shows that it was not caused by simple resonance as was once believed. Instead, the bridge collapsed due to a process called aeroelastic flutter, where aerodynamic forces coupled with the structure’s natural mode of vibration to produce rapid periodic motion.
Given that the Tacoma Narrows Bridge incident was not caused by resonance, it raises the question of whether there are any other phenomena in mechanics that are commonly misattributed to resonance. In this article, we’ll take a deeper dive into the concept of resonance and explore whether there are any other examples of mislabeled resonance phenomena.
Defining Resonance
Before we delve into specific examples, let’s take a moment to define what we mean by resonance. In mechanics, a system that can be described by a differential equation is said to resonate when the amplitude or energy of the system is maximized at a particular frequency. This frequency is often called the resonance frequency.
A simple example of resonance can be seen in a swing. Consider a swing with a person sitting on it. If you start pushing the swing, you’ll notice that the swing starts oscillating back and forth. If you push the swing at the right frequency, you’ll be able to amplify its motion, causing it to swing higher and higher until the person on the swing is almost touching the sky. This is an example of resonance.
The Tacoma Narrows Bridge Fallacy
As mentioned earlier, the collapse of the Tacoma Narrows Bridge is often cited as an example of resonance. However, a more nuanced analysis of the incident reveals that it was caused by aeroelastic flutter rather than simple resonance.
The Tacoma Narrows Bridge was a suspension bridge that spanned the Tacoma Narrows strait of Puget Sound in Washington State. The bridge opened in 1940, but just four months after it opened, it collapsed due to strong winds. The incident was captured on camera and became famous around the world.
For many years, it was widely believed that the reason for the bridge’s collapse was resonance. It was thought that the wind was causing the bridge to vibrate at its natural frequency, which caused the amplitude of the vibrations to increase until the bridge collapsed. However, further analysis showed that the collapse was not due to resonance, but rather aeroelastic flutter.
Aeroelastic flutter is a phenomenon where the aerodynamic forces on an object couple with the structure’s natural mode of vibration to produce rapid periodic motion. The wind caused the bridge to start oscillating, which in turn caused the wind to generate more aerodynamic forces. These forces fed energy into the structure’s natural vibration mode, causing the amplitude of the oscillation to increase until the bridge collapsed. This is a different process than simple resonance, and highlighting it helps to clarify what’s happening in these types of incidents.
Other Misattributed Resonance Phenomena
While the Tacoma Narrows Bridge collapse is a well-known example of a misattributed resonance phenomenon, it’s not the only one. There are many other mechanics phenomena that are sometimes mistaken for resonance phenomena. Here are a few:
Damping
Damping is a process where a system gradually loses energy due to friction or other damping forces. When a system is damped, its resonance frequency shifts, making it less susceptible to resonance. Damping can be mistaken for resonance if the reduction in amplitude is not taken into account, leading to false claims that the system is resonating.
Beats
Beats are another example of a phenomenon that can be mistaken for resonance. When two sound waves of slightly different frequencies are played together, the interference between them causes the sound to fluctuate in loudness. This fluctuation is called a beat, and it can be confused with resonance because it has a similar periodic nature. However, beats are not resonating because the sound wave is not matching the structure’s natural frequency.
Forced Oscillations
Forced oscillations are yet another example of a phenomenon that is often confused with resonance. When a system is subjected to a periodic force, it can start oscillating at the same frequency as the force. This is often confused with resonance, but the key difference is that the system is forced to oscillate, rather than being naturally driven.
Conclusion
While resonance is an important concept in mechanics, it’s not the only process that can cause a structure to vibrate or fail. In some cases, other processes like aeroelastic flutter, damping, beats, or forced oscillations can be mistaken for resonance phenomena. By understanding the differences between these processes, we can better understand how structures behave, and ultimately, design better structures that are less prone to failure.
Phenomena Which are Incorrectly Declared As Resonance Phenomena?
When studying physics, one of the fundamental concepts that you’ll come across is resonance. The term refers to a phenomenon where a system vibrates at the same frequency as an external force. One of the most famous examples of resonance that students are taught is the collapse of the Tacoma Narrows Bridge. However, a closer look at this incident shows that it was not caused by simple resonance as was once believed. Instead, the bridge collapsed due to a process called aeroelastic flutter, where aerodynamic forces coupled with the structure’s natural mode of vibration to produce rapid periodic motion.
Given that the Tacoma Narrows Bridge incident was not caused by resonance, it raises the question of whether there are any other phenomena in mechanics that are commonly misattributed to resonance. In this article, we’ll take a deeper dive into the concept of resonance and explore whether there are any other examples of mislabeled resonance phenomena.
Defining Resonance
Before we delve into specific examples, let’s take a moment to define what we mean by resonance. In mechanics, a system that can be described by a differential equation is said to resonate when the amplitude or energy of the system is maximized at a particular frequency. This frequency is often called the resonance frequency.
A simple example of resonance can be seen in a swing. Consider a swing with a person sitting on it. If you start pushing the swing, you’ll notice that the swing starts oscillating back and forth. If you push the swing at the right frequency, you’ll be able to amplify its motion, causing it to swing higher and higher until the person on the swing is almost touching the sky. This is an example of resonance.
The Tacoma Narrows Bridge Fallacy
As mentioned earlier, the collapse of the Tacoma Narrows Bridge is often cited as an example of resonance. However, a more nuanced analysis of the incident reveals that it was caused by aeroelastic flutter rather than simple resonance.
The Tacoma Narrows Bridge was a suspension bridge that spanned the Tacoma Narrows strait of Puget Sound in Washington State. The bridge opened in 1940, but just four months after it opened, it collapsed due to strong winds. The incident was captured on camera and became famous around the world.
For many years, it was widely believed that the reason for the bridge’s collapse was resonance. It was thought that the wind was causing the bridge to vibrate at its natural frequency, which caused the amplitude of the vibrations to increase until the bridge collapsed. However, further analysis showed that the collapse was not due to resonance, but rather aeroelastic flutter.
Aeroelastic flutter is a phenomenon where the aerodynamic forces on an object couple with the structure’s natural mode of vibration to produce rapid periodic motion. The wind caused the bridge to start oscillating, which in turn caused the wind to generate more aerodynamic forces. These forces fed energy into the structure’s natural vibration mode, causing the amplitude of the oscillation to increase until the bridge collapsed. This is a different process than simple resonance, and highlighting it helps to clarify what’s happening in these types of incidents.
Other Misattributed Resonance Phenomena
While the Tacoma Narrows Bridge collapse is a well-known example of a misattributed resonance phenomenon, it’s not the only one. There are many other mechanics phenomena that are sometimes mistaken for resonance phenomena. Here are a few:
Damping
Damping is a process where a system gradually loses energy due to friction or other damping forces. When a system is damped, its resonance frequency shifts, making it less susceptible to resonance. Damping can be mistaken for resonance if the reduction in amplitude is not taken into account, leading to false claims that the system is resonating.
Beats
Beats are another example of a phenomenon that can be mistaken for resonance. When two sound waves of slightly different frequencies are played together, the interference between them causes the sound to fluctuate in loudness. This fluctuation is called a beat, and it can be confused with resonance because it has a similar periodic nature. However, beats are not resonating because the sound wave is not matching the structure’s natural frequency.
Forced Oscillations
Forced oscillations are yet another example of a phenomenon that is often confused with resonance. When a system is subjected to a periodic force, it can start oscillating at the same frequency as the force. This is often confused with resonance, but the key difference is that the system is forced to oscillate, rather than being naturally driven.
Conclusion
While resonance is an important concept in mechanics, it’s not the only process that can cause a structure to vibrate or fail. In some cases, other processes like aeroelastic flutter, damping, beats, or forced oscillations can be mistaken for resonance phenomena. By understanding the differences between these processes, we can better understand how structures behave, and ultimately, design better structures that are less prone to failure.