Absorption spectroscopy is popular form of chemical identification and characterization. Typically, light is passed through a sample once and the intensity of the light after passing through the sample is measured. If light is absorbed by a sample, we expect the amount absorb to increase if the concentration of the solution or the thickness of the solution is increased. Absorbance is defined so that we expect the amount of light absorbed to have a linear dependence of thickness and concentration.

Sometimes samples do not absorb a lot of light, so measuring their weak absorbance is difficult. To solve this problem, cavity-enhanced absorption spectroscopy can be used. This method uses a set of mirrors placed around the sample to reflect light through the sample multiple times. This effectively increases the thickness of the sample, making the observed absorbance stronger and more easily measurable. However, this method has been seen to break the linear relation between absorbance and concentration. Instead of seeing a straight line when plotting absorbance versus concentration, they see a curve.

My junior independent study work was to investigate the absorbance dependence on thickness. I used a cavity-enhanced method and a typical single pass method to take absorbance measurements for varied sample thickness. I varied the thickness by using different sizes of sample container. From my experiments, I saw the predicted linear behavior for the single pass data. However, for my cavity-enhanced data I saw a curved trend like had been observed previously for varied concentration. This tells me that the amount that the cavity enhances the measurement depends on how much absorber or sample the light must pass through.

My name is Collin Hendershot. For my Junior Independent Study project I observed the effect of concavity on the aerodynamics of high speed automobiles. The two important aerodynamic characteristics of automobiles are downforce and drag. Downforce is the force of air pushing a car toward the road and drag is the force on the car from air opposing the forward motion of the car. Downforce increases a car’s stability and turning speed, and drag decreases a car’s top speed and fuel economy. An aerodynamically efficient car will have a high downforce to drag ratio. To increase a vehicles downforce designers often include a rear wing on the car. I designed 5 different rear wings with a leading edge defined by the function

which creates wings with increasing concavity as the value for a increases (Figure 1). The downforce and drag for each wing was recorded and then the downforce to drag ratio of each wing was calculated. The results are pictured in Figure 2 and the a = 2 wing design has the largest downforce to drag ratio, 3.8, therefore it is the most efficient wing design.

I have always thought that one of the most outdated technologies we currently employ in the large scale is propellers for ships. While this isn’t a critical fault in our world it does lead to a lot of inefficiencies. Modern trade ships and super-tankers use millions of tons of fuel annually. This does a great deal of damage to the environment. Air travel was also largely propeller based at its inception, but since then several new types of engine have been developed. Most notably the Scramjet engine ingests air and mixes it with fuel at supersonic speed, exhausting the combustion results to produce thrust. This is a highly effective method of producing thrust, one which has been able to produce speeds of Mach 12. For reference, at Mach 12 one could travel the entire distance of the equator in less than three hours. I believe that it is possible to take some of the principles of the Scramjet engine and develop a version for generating thrust underwater.

My project was to simulate this new kind of underwater propulsion system to determine whether or not it could feasibly operate. I did this by working with legacy code provided by another student that simulated air flowing through a channel. I modified the code to simulate water flowing through the channel, and also added a simple structure to represent a simple Scramjet style water propulsion device, shown above as the red boxes. The simulated Scramjet water propulsion system used heat as a fuel source, this is done by simulating the result of water boiling so quickly it evaporates with explosive force. This is shown with the gray boxes in the center, within each of these the simulated water gets “kicked” in a random direction and gains a high speed. The results of my simulation were inconclusive but I did show that the Scramjet Structure had an effect on the operation of the system. I believe with enough tweaking this simulation would show that such a system would operate in the real world.

Solar sails utilize the change in momentum of photons as a means of propulsion. This allows spacecraft with solar sails to significantly reduce their mass, since they do not have to carry onboard fuel (in comparison to traditional rocket-based spacecraft). This project aims at designing a program to display the dynamics of a solar-sail-based spacecraft in the presence the Sun and Earth.

Depending on the orientation of the sail, it is possible to sail towards or away from the Sun and achieve a variety of orbits. The video shown above displays the program, with the Sun in red, the Earth in blue, the sail in white, the sail’s previous position in purple, and the sail’s position with respect to the Sun in yellow.

This project uses an electronic circuit to demonstrate something called stochastic resonance. Stochastic resonance (SR) is present many places in nature–from dictating the timing of ice ages to aiding in fish hearing. So, what is it? SR is simply when a random noise signal serves to boost the strength of another, cleaner signal. Audio is a good way to think about this. Imagine you are listening to a song, but the volume is so low that you cannot hear it. Then you add another speaker playing random noise. You start to turn up the noise, and at a certain point, you start to hear the song. This is pretty strange, and quite counterintuitive. Usually adding noise drowns out other sound, so how could random noise serve to boost a sound? This project seeks to examine that question by observing stochastic resonance in a circuit. Every signal running through the wires I used could easily be sent to a speaker and played aloud, as all of the frequencies involved are within the auditory range.

The circuit used here is called a Schmitt trigger. Its purpose here is to allow a signal to pass through if it is strong enough, but block weaker signals. The point at which the signal is strong enough to pass through the Schmitt trigger is called the threshold voltage. One other side effect of the Schmitt trigger is that the output signal will be a square wave rather than a sine wave. I ran a strong signal through at first to confirm that the circuit was operating as it should, then I ran a weak signal through and saw that the output disappeared. At this point, we have a weak signal entering the circuit, but no output, just like when you were playing a song, but it was too weak of a signal for your ear to register. So, I then added random noise to my signal. The random noise makes the input sign wave cover a larger range of voltages, puncturing the threshold voltage, and once again allowing the circuit to output a square wave. This is stochastic resonance in a hysteretic circuit.

Using this circuit I was able to determine the best possible noise volume to cause SR in the given parameters. The circuit itself could be used to make a hearing aid that listens for cleaner weak signals and filters out excess noise. This circuit is also interesting as a metaphor for other things in nature, as it behaves similarly to the human neuron.

The purpose of my experiment was to analyze whether the behavior of an RLC (Resistor, Inductor, Capacitor) circuit is noticeably affected by replacing the inductor with an oscillating spring. Common inductors take the form of solenoids which are helical coils of wire that are wrapped around a core. This core can be made of different materials, but some of the more common are ferromagnetic materials like iron, cobalt, or nickel. The core can also just be air, which is similar to the model that the spring mimics.

When a current starts to run through an inductor, the inductor resists the current. After a brief period of time, the inductor will no longer resist the current and the system is in equilibrium. If the current changes, however, the system will no longer be in equilibrium and the inductor will once again try to resist the change. In order for the inductor to resist the change, there must be some sort of force that it applies to the current. It turns out that this force is exerted through the use of a magnetic field acting on the current. Therefore, we say that if the current changes, it induces a magnetic field that resists the change in the current. This is a reciprocal relationship, too. If instead, the magnetic flux (the amount of magnetic field flowing through the area of the inductor) changes, then a current will be induced that opposes the changing flux.

By exploiting this trait of inductors, my hope was to see significant change in the output voltage of my circuit. For an RLC circuit, the output voltage is dependent on the frequency that is driving the circuit. For certain frequencies, the output voltage will be approximately zero, whereas for other frequencies, the output voltage will be immense. The curve on a graph of output voltage as a function of frequency is called the resonance curve and the maxima of this curve is referred to as the resonant frequency. The width of the curve as well as the location of the resonant frequency are dictated by the inductance in the circuit. The inductance of an inductor is dependent on some of its geometrical properties such as its length and radius. Therefore, with a spring, the geometry can be altered and inductance can be actively changed as the circuit is running.

When I placed the spring in the circuit, I was able to observe the resonant frequency shifting to different values by stretching or compressing it. For one trial, a mass was suspended from the spring and the mass/spring system was made to oscillate. During the period of oscillation, the inductance of the spring was constantly changing which meant the inductor was continuously responding to changes in current and magnetic flux and resisting them accordingly. While observing the electrical, sinusoidal signal passing through the circuit on an oscilloscope, I could actually see the amplitude of the signal changing corresponding to movement of the spring. See attached video in order to watch this phenomenon.

For my Junior Independent Study, I looked into some cool physics videos to find an interesting topic to explore. I found a youtube video about the University of New Mexico Couette cell apparatus for demonstrating laminar flow and decided that watching fluid blend together and then separate out again was an interesting concept. The project I designed was to bring this apparatus to the College of Wooster and then experiment with it. I looked into how accurately a line of color could be returned to its original location after being rotated at various angular velocities and if the transition was more accurate at varying depths below the surface of the fluid.

Walking – we all do it. But why do we walk so often? Why doesn’t everyone skip down the block to work?

Aside from that being deemed as weird by society, walking is the most efficient way for people to move on earth due the gravity here. We’ve all experienced this in some way. You probably know that it’s much easier to walk long distances, than to run them. In my Clare Boothe Luce work this year, I confirmed that walking is amazingly efficient by simulating a passive walker that is able to walk down a hill simply through the force of gravity.

My Junior IS study “Building a Passive Robot for Active Learning,” aimed to take this simulation research and create a real passive walking robot (a robot without a motor) out of plastic Tinkertoys. I used a previous study done by a group at Cornell to base my walker design off of and to use as a comparison. When they built their robot in the 1990s, wooden Tinkertoys were mass-produced, but now plastic Tinkertoys are the only financially possible option. I found that the walkers behaved slightly differently due to sensitivity to initial conditions and parameters for passive walkers. Though this difference exists, I proved that it is still possible to create this simple passive walking robot.

The hope is that this walker could be used as an outreach tool at Science Days at the College of Wooster in order to introduce kids to engineering and to make mechanics a more approachable topic to them. This project is a fun way to spark children’s imaginations and learn more about how fascinatingly efficient human movement can be.

This spring, each Wooster Junior physics major undertook a six-week scientific investigation of their own design, as a part of our junior independent study course. Watching their projects come to fruition over the course of the semester was a very rewarding experience for me, and I am happy to announce that each junior prepared a blog post on their project. These will be posted shortly as a series of guest blogs, so please stay tuned!