Experiments
Effects of Changes in Temperature on the Speed of Sound
1) ABSTRACT
Sound travels in waves of compression through a medium. Changes in the medium such as density and temperature can affect the speed of sound. Using a device that uses a calculation based on a set speed of sound, researchers can use the changes in the measured length of a fixed distance to determine the change in the speed of sound. This experiment used changes over the course of a high altitude balloon launch in the measured length of tube to measure the correlation between temperature of medium and speed of sound when other factors are held constant. The experiment supports the idea that the speed of sound decreases as temperature decreases, and vice versa, as predicted by the kinetic molecular theory of gases.
2) INTRODUCTION
Sound travels by waves of compression between particles in a medium. The first group of particles presses up against the next group of particles and then goes back to where it was, while the next group presses against the one after that. This cycle continues until the sound has travelled a long way and/or dissipated. A sound wave with a high frequency has a high pitch and contains many areas of higher pressure passing a certain point in one second. A soundwave with fewer areas of relatively high density passing a certain point within one second has a lower pitch. A sound with a high amplitude has a high pressure in these areas, and a sound with a low amplitude has a relatively low pressure in those waves.
The speed of sound depends on the temperature and the medium. The medium for our experiment, air, will remain constant during the flight, although the temperature will vary over the course of the experiment. According to the kinetic-molecular theory of temperature, a gas (in our case, air) with a high temperature has a high kinetic energy of individual gas molecules at the particle level. Therefore, sound in a gaseous medium with a high temperature has a faster velocity than sound in a medium with a low temperature because the particles in the air have more energy and should be able to move and compress more quickly. Because of the measurable temperature difference, we will be able to measure the difference in the speed of sound between the system at elevation and the system under usual temperature conditions.
The researcher chose this topic to learn more about the way sound waves move and work. The idea was inspired by the sponsor of NTHS club.
3) METHODS AND MATERIALS
We obtained an Ultrasonic Distance Sensor - HC-SR04. This device measures distances by emitting sound at 40 Hz and measuring the amount of time needed for the sound to echo back. The speaker automatically turns this measurement into the distance, in cm, from the opposite edge of the container, based on the assumption that the speed of sound remains constant at 340m/s. We placed this device on one side of a 15cm PVC tube. The tube was sealed shut on both ends with rubber caps and duct tape. This distance should remain constant throughout the duration of a high altitude balloon flight with large changes in temperature. Using the relative change in the distance measured by the sensor, we were able to measure the relative change in the actual speed of sound. This tube was then placed in a Styrofoam pod as part of the payload of a high altitude balloon launch and exposed to the low temperatures of near space. The sensor collected data every second and recorded it to a Raspberry Pi. Data from experiments conducted by other researchers were also recorded to the same Raspberry Pi.
While testing the setup prior to launch, the researcher noticed that the data seemed to be faulty. The sensor was replaced with another sensor of the same type. However, there was no change in the results. Possible explanations for the reason the data appeared to be faulty are discussed in the discussion section.
4) RESULTS
After removing the outliers (over one trillion, or 1*1012) and examining only the data from the duration of the flight, the time for the sound to travel through the tube and back was graphed. The perceived distance remained fairly constant around 15cm with a moderate, steady increase toward 20cm for the first 90 minutes. The increase in perceived distance means that the speed of sound was slower than at the beginning of the flight. At around 12:10 UTC, the perceived distance nearly doubled and started to read steadily around 35cm. At around 12:25, the perceived distance once again jumped, this time to nearly 60cm. After 12:30, no data are available because all data received from this time until the end of the launch measure over one trillion and do not fit with the rest of the data.
The temperature was also measured during this time. However, the temperature and time data do not seem to have been reliable, as the recorded time of day, used as a reference for the flight, did not follow in a logical order on the same device as the one used to record temperature. The temperature measured in previous high altitude balloon flights can give us a good idea of the general trends the temperature should have measured. The temperature in the pod should have decreased to below zero, gradually increased, and quickly decreased again.
5) DISCUSSION
The frequent outliers ten orders of magnitude larger than the majority of the data are likely the result of the signals bouncing around within the tube instead of travelling directly to the end of the tube and returning. With the outliers removed, the general trends in the data become more clear.
The perceived distance of the tube gradually increased over the course of the first part of the flight. This should correspond to a decrease in temperature during this time. This part of the results proves that the speed of sound decreases as temperature decreases, as predicted by the kinetic molecular theory of gases.
It is possible that the cap on the end of the tube opposite the sensor came off. This would have caused the increase in the measured distance of the tube. The lid to the pod may have come off in stages, leading to the further increase in measured distance. Eventually, the sound would have lost any nearby barrier to bounce off, causing the sudden increase in the value and quantity of outliers. The cap falling off would also have led to a decrease in the air pressure of the sound’s medium, further decreasing the speed of sound.
6) CONCLUSION
If all other variables are held constant, the speed of sound in a gaseous medium decreases when the temperature of the medium decreases, and increases when the temperature of the medium increases. This supports the hypothesis, which was based on the kinetic molecular theory. This also supports the kinetic-molecular theory.
Recommendations
For further research on this topic, the researcher would suggest that a similar experiment be conducted without being sent into space. The perceived length of the tube and the temperature inside the tube could be measured in the lab. The tube could then be placed in a refrigerator or freezer, with data on the perceived length of the tube and the temperature in the tube being recorded to a Raspberry Pi, for one hour. The tube could then be moved back into an area at standard temperatures. The measured length of the tube could be graphed as a function of the temperature as measured in the tube, which would provide clearer support for the hypothesis. This experiment could also help find an equation relating the speed of sound and temperature based on the slope of the line graphed.
Gravitational Redshift/Blueshift
1) Abstract
Light can be used to gauge the distance of distant galaxies bordering the edge of our visible universe. Being able to understand how it warps and shifts with gravity could help show areas of higher or lower gravity in space, showing us where previously unseen planets or galaxies are located. The understanding of light's relation to gravitational force could also help scientists locate black holes and their relativity to earth. This experiment set out to prove that at our estimated final altitude the difference in gravitational strength would not be great enough to cause any visible shift. This experiment also set out to prove that if the relation of the observer to the light was constant then a visible shift could not be recorded. More than anything this experiment set out to improve our knowledge on gravitational fields and how light interacts with them. This experiment had some difficulties yet it was still able to provide adequate results, from which a conclusion could be drawn. During the course of the flight which this experiment was on the lights amplitude was measured every two seconds. The final results showed that gravitational Redshift did not occur during the course of the experiment, nor did gravitational blueshift occur during the course of the experiment.
2) Introduction
Gravitational Redshift-Blueshift is a result of light entering or exiting a gravitational well. Light is incapable of moving any faster or slower than the speed of light unless it’s traveling through a denser medium, so in order to make up for the difference in gravitational strength the light will increase or decrease the amount of exerted energy. This shift in energy exertion is done to help the light more efficiently move through the new gravitational field. As the light's energy exertion changes so does the wavelength, frequency and consequently the color. The light’s color will begin to shift towards red in higher fields of gravity or blue in lower fields of gravity.
Gravitational Redshift Blueshift has been observed towards the end of our view of the universe, and it has also been observed as light tries to escape the gravitational field of a black hole. Gravitational Redshift blueshift has been tested once before in the Pound-Rebka experiment however that was measuring the Doppler shift. This experiment placed two lights at the top and bottom of a tower putting 22.5 meters of space in between the two. These lights were shown into sensors placed in direct opposition to the lights. Since the lights and sensors were located at different levels the sensors were able to capture the light moving throughout gravitational wells.
The changes observed in this experiment were microscopic however they were present. These shifts showed that as the light was traveling from the top of the tower down towards the basement the light shifted towards blue, and the light shifted towards red while traveling up from the basement. However this experiment counted on the lights being in different fields, whereas our experiment has the lights and the sensors in the same position and field.
There are a few restrictions to this experiment though, with the main one being the type of results that can be recorded. The AS7262 measures light amplitude whereas the original experiment planned to measure frequency. Still the sensor is sensitive enough that the results can be clearly interpreted either way. Since the light will be in the same position and gravitational field there is no possibility that the sensor could capture the light moving through a new field of gravity. With this knowledge it is reasonable to assume that if the sensor is recording at the same level and position as the light source then no observable shift will be made.
3) METHODS
The AS7262 sensor was tested at ground level to get the initial amplitude reading. After the initial testing and calibration was completed, the sensor was placed in the center of the payload accompanied by a weight sensor and real time clock. The payload was lined with black felt on all sides to prevent any ambient light from interfering with the sensor. This sensor had a blue LED emitting a frequency between 460 and 475 and attached to the ceiling immediately above the sensor. This blue LED was soldered on alongside a red LED so that any shifting will be clearly visible. The red LED was emitting a frequency between 620 and 650. The lights are around three centimeters away from the sensor and they are facing down.
The sensor was connected to the Raspberry Pi and suspended by metal pillars which were four centimeters tall. Once it had been set up the payload was attached to a weather balloon and sent up 100,000 feet and re-recorded every two- four seconds during the flight. The AS7262 Sensor had six channels each measuring different light colors and amplitudes. As the balloon ascended the 6-channel visible sensor continued to monitor which color of light has the strongest amplitude reading. If another color of light begins to read at a higher amplitude then we can mark a shift towards the red or blue end of the spectrum. All of these results were recorded by the sensor and put into a table so that comparisons of the amplitude readings were clearer.
4) RESULTS
There were some issues with the spectral sensor which effected the results of the final experiment. The photodiode intended to record blue light didn’t function so there were no results concerning the blue LED. The Spectral Sensor did record the red and the violet readings however there was no clear evidence of a color shift. This implies that throughout the entirety of the flight there wasn’t even a 0.00001 microwatt difference. This is completely illogical as on earth there were a multitude of miniature differences in the lights amplitude. The LEDs likely could not have put out a constant stream of photons which all had the same amount of energy. Unlike the Pound Rebka experiment, there was no evidence supporting that the results could possibly have stayed so consistent the entire flight as the LEDs were inconsistent even at ground level. Still the results were worth examining and since the results were consistent down to the 0.00001 microwatts there is no evidence of a shift.
During the flight there were brief periods of time where the sensors were reading as zero, however when assessing the data those were perceived to be technical errors. After the flight ended the results could be checked and these were the amplitude readings of the measured colors. The red LED was reading at 0.8808 μW/cm2, and the violet LED was reading at 1.21268 μW/cm2. Since blue wasn’t recording the red LED’s amplitude was subtracted from the violets LED amplitude to find the estimated blue amplitude. As a base estimate the blue LED was reading at 0.33188 μW/cm2, yet this cannot be proven.
Since the flight data was effected by technological issues there is no real way to know whether a shift occurred. There may have been a blue shift which wasn’t recorded due to issues with the spectral sensor, or the reading may be correct. Though since the difference in gravitational strength was so slim and the light was always in the same field as the observer there was little to no possibility any shift would occur. Using this logic the consistency is still abnormal but proves the hypothesis to be correct. Since there was no shift in the amplitude of either recorded colors, it is safe to say that gravity did not affect the frequency or amplitude of the light being emitted.
When creating the graph blue, red and violet were graphed. Blue was graphed for the sake of making the results slightly more understandable. An area graph was used since the consistency made other forms of graphs seem incomplete or unprofessional. The area graph also shows the consistency in a more visually interesting manor. To organize the graph more effectively, the time was marked by every ten minutes. Since the flight lasted two hours and 12 minutes, the points the time was marked every ten minutes. The colors used for the graph are also the colors of the light being graphed. The purple light is marked by the purple points and the red light is marked by the red points and the blue light is marked by the blue points.
After retrieving the 3-in-1 it was re tested in an attempt to figure out the problem. The LEDs were not being recorded at all and the sensor could only pick up the amplitudes of the ambient light. These results showed the slight differences missing in the final experiment, some of the colors were still consistent. When the tests were performed using ambient light all of the colors of the visible light spectrum were present. The original test format was designed to limit this for the sake of consistency. This test showed that the problem had to have been with the LEDs since all of the sensors were reading perfectly. The main point of this test was to ensure that the sensor wasn’t broken and to gather some usable data for comparison. Both of those were achieved and during the next rendition of this test these results can be used as a base and expanded upon.
5) DISCUSSION
The purpose of this experiment was to prove that there would be no observable Redshifting or Blueshifting within the earth’s upper atmosphere. Despite technical issues, if the results can be considered reliable, then the initial hypothesis was proven correct. With an estimated final height of 100,000 feet, there will be no recorded shift because the sensor and light will always be in the same field of gravity. By completing this experiment it provided more information about the shift in gravitational force within our planet's gravitational well, while also helping demonstrate how light interacts with the earth’s gravity at different levels of the atmosphere.
6) CONCLUSION
Using what data could be retrieved from the SD card as well as trusting that technical difficulties didn’t corrupt the experiment, it was proven that light does not shift towards red or blue in the upper levels of the earth’s atmosphere. This experiment has the possibility to expand on what is known about light's reactions to gravity, as well as strengthen knowledge concerning earth’s atmosphere. Despite setbacks, this experiment can be repeated and each rendition will teach something new. This experiment has the possibility to expand our knowledge about everything from physics to color theory. With the reproduction of this test we can become more familiar with Earth’s atmosphere and light's reactions to it.
As a final conclusion the results showed no visible shift. However, with improved technology this test can be expanded on and redone for more accurate results.
7) References
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