Can You Hear Sounds in Outer Space?
AbstractHave you ever wondered what sounds you can hear in space? The answer is simple: none! In outer space there is utter silence. There are no sounds of traffic jams or thunderstorms or crashing waves. No buzzing bees or babies crying. Just silence. In this experiment, you will discover why empty space is void of sound and prove it with the help of the microphone in your phone and a sensor app.
Edited by Svenja Lohner, PhD, Science Buddies
ObjectiveThe goal of this project is to measure how decreasing the amount of air and creating a vacuum in a container affects the sound intensity of a buzzer inside.
"Could I get some peace and quiet around here?" We have all longed for a moment of silence. But even if our brother stops talking and our baby sister stops crying, we would still be able hear the traffic on the freeway or the neighbor's dog barking. What causes these sounds? Will we ever be able to get some peace and quiet?
Sound is produced by vibrations from material objects. These vibrations move in waves that travel through a medium such as gases (like air), liquids (like water), and solids (like the ground). Our ears hear sound when these waves reach our eardrums as shown in Figure 1. The sound waves then cause the bones in our middle ear to vibrate and the vibrations are transmitted to fluid in our inner ear. Then the vibrations travel to the inner ear hair cells and to the nerves that carry the signal to our brains.
When sound waves enter a human ear they travel past the outer ear until they hit the ear drum. The ear drum vibrates air trapped in the inner ear and a nerve sends a signal to the brain which can decipher the vibrations as different sounds.
Figure 1. Hearing sounds with our ears.
Scientists describe different sound waves by their amplitude (how loud the sound is) and frequency (the pitch of the sound). The intensity of sound is measured in decibels (dB). Figure 2 shows the decibel ratings of some common sounds. Decibels are a logarithmic scale, not a linear scale. This means that for every increase of 10 dB, the sound intensity increases by a factor of 10. For example, sound with an intensity of 40 dB is 100 times as intense as 20 dB, not twice as intense. However, while we may use the terms interchangeably in everyday speech, loudness and intensity are not the same thing. (See this link for a more detailed explanation). Most of us perceive a sound to be "twice as loud" as another one when they are about 10 dB apart. Sound levels above 80 dB can cause hearing damage over long periods of time, and sound levels above 120 dB can cause immediate damage.
A bar graph measures common sounds in terms of decibel levels from the loudest at the top to the softest at the bottom. A gunshot is the loudest common sound with a value of 140 decibels, a normal conversation has a value in the middle of the graph of 60 decibels, and the sound of breathing is the quietest with a value of 10 decibels.
Figure 2. Decibel levels of some common sounds. Remember that the decibel scale is nonlinear. Every increase of 10 dB corresponds to roughly doubling the perceived loudness of the sound. So, for example, a chainsaw (100 dB) does not sound twice as loud as moderate rainfall (50 dB); it sounds 32 times as loud!
In this experiment, you will demonstrate what happens to sound if it does not have a medium to travel through. You will simulate conditions in outer space by creating a vacuum and measure how this affects the sound intensity of a buzzer using the microphone in your phone and a sensor app.
Terms and Concepts
- Decibels (dB)
- How do our ears hear sound?
- What makes sounds louder or softer?
- What makes sounds high pitched or low pitched?
Materials and Equipment
- Strong metal wire (diameter about 0.8 mm, circa 15 cm long)
- Wire cutter or scissor
- 9V battery
- Buzzer; available from Jameco
- Strong tape, such as gaffer tape
- 500 mL flat-bottom (Erlenmeyer) flask, made of borosilicate glass (so it can be heated without breaking) with tightly fitting rubber stopper; available from Amazon
- Heat source (stove or Bunsen burner)
- Hot mitt
- Smartphone with a sensor app such as phyphox, available for free on Google Play for Android devices (version 4.0 or newer) or from the App Store for iOS devices (iOS 9.0 or newer).
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Note: In this science project, you will investigate how sound intensity changes with decreasing air pressure. You will use a phone equipped with a sensor app to record the sound of a buzzer in a flask while a vacuum is created inside. Sensor apps such as phyphox let you record data using sensors that are built into many smartphones, including a microphone that you can use to measure sound. While recording the buzzer's sound, the app creates a graph that will show you how loud the buzzer is over time, measured in decibels, the unit for sound intensity.
- Cut the wire to a length of about 12–15 cm using a scissor or a wire cutter.
- Fold the wire over the 9V battery in between the plus and minus pole as shown in Figure 3.
Figure 3. Wire folded over 9V battery.
- Poke both ends of the wire into the inside of the rubber stopper to make a loop in which you can insert the battery as shown in Figure 4 on the left. Make sure the wire does not poke out of the stopper on the other side.
- Insert the 9V battery into the wire loop with the pole side facing down or away from the stopper. It should look like shown in Figure 4 on the right.
Figure 4. Create a wire loop (left) to attach the battery to the stopper (right).
- Open the sensor app on your phone and select the sound sensor (audio amplitude in phyphox). Note, that when you are using the phyphox app you will have to calibrate the audio amplitude sensor (sound sensor) before you do any measurements. Do this calibration before you start your investigation, so you get correct sound intensity readings. To calibrate your sound sensor in phyphox, follow the instructions in the sound sensor calibration video. You will have to re-calibrate the audio amplitude sensor (re-set the decibel offset) every time your start a new recording! Once you have calibrated the sensor, make sure you know where the microphone is located on your phone and do a quick test to see if your sound measurement is working. For example, you could record yourself clapping or singing to check if the sensor behaves as expected.
- Once you have confirmed that the sensor works and you are familiar with the app, you can start with the experiment. You should do this experiment in a quiet environment. The background reading of your sound meter when there is no noise in the room should be in the range between 20–40 decibels (dB).
- To start the experiment, add about 4–5 tablespoons of water to the flask to a depth of about 0.5 cm.
- With the flask open (with the stopper and buzzer still off the flask), place the flask on the heat source and bring the water to a boil. Boil for one timed minute. Do not allow the flask to boil dry.
- While the water is boiling, use strong gaffer tape to tape the buzzer onto the battery.
- Connect the long pin of the buzzer with the plus pole of the battery and the short end with the minus pole of the battery (Figure 5 top picture). When connected correctly, the buzzer should make a loud beeping sound.
- Use strong tape to attach the buzzer to the battery. Wrap the tape around the buzzer and battery a couple of times to make sure it stays in place. Do not place any tape on the hole on top of the buzzer as this is where the sound is coming from.
- Your setup should look like in the bottom picture of Figure 5.
Figure 5. Connect the buzzer to the battery and attach it tightly with gaffer tape.
- Once the water has boiled for one minute, switch off the oven or Bunsen burner. Then put on your oven mitts and carefully remove the flask from the heat source.
- Quickly place the stopper with the attached battery and beeping buzzer into the flask. Make sure to insert it tightly and do not let the battery or the buzzer touch the glass inside the flask, otherwise it will not work. Caution! The glass will be hot! Take care not to touch the flask with bare hands and note that the stopper, once inserted, can pop out again as the water vapor inside the flask creates an overpressure. Be careful to not burn your hands in the hot steam in case the stopper pops out again!.
- As soon as the stopper is safely and tightly secured in the flask, start the sound sensor recording by pressing the play button in the phyphox app and place the flask on top of your phone as shown in Figure 6.
Figure 6. Final setup for recording the sound intensity of the buzzer inside the flask.
- While the app is recording the sound intensity of the buzzer, observe the flask and also listen with your ears.
- Note the condition of the inside of the flask. For example, is the air inside the flask clear? Do you see condensation (water droplets) on the sides of the flask?
- Note your observations of the sound. How loud is the buzzer at the beginning? Does the sound get louder or quieter over time?
- After about 10–15 minutes, or when the flask has cooled to room temperature, the trial is complete. Take the flask off the phone and press the pause button to stop the recording. Make sure to save your data.
- Keep observing as you prepare the next trial. For example, is it harder to remove the stopper now than when you first put it in?
- For any experiment, it is important to do multiple trials to assure that your results are consistent.
- Repeat the experiment at least two more times, and record the results of each trial. Before each recording, make sure your sound sensor is still calibrated and recalibrate it again (re-set the decibel offset) if necessary.
- Add more water to the flask, if needed.
- Analyze your data that you recorded with the sensor app.
- Open the graphs for each of your trials in the app which show how the sound intensity changes over time after the flask is sealed. Your data should look something like the graph in Figure 7. The sound intensity should decrease over time and should level off at the end. You can use the 'pick data' tool within phyphox to select individual data points and display their time as well as the measured sound intensity.
- What was your sound intensity (in decibels) at the beginning, what at the end?
- How fast did the sound intensity decrease, or how long did it take for the sound intensity to level off? Select the data point when you started the the experiment (at the highest sound intensity) and when it was finished (where it started to level off). For example, in Figure 7 the highest sound intensity (56.99 dB) was at 11.4 seconds and it leveled off at about 31.66 dB after 545.7 seconds. Calculate the time difference between these two points. In Figure 7 this would be 545.7 s - 11.4 s, which is 534.3 s.
- Make a bar graph in which you show the sound intensity (measured in decibels) on the y-axis at the beginning and end of the experiment. Calculate the difference between both values. By how much did your sound intensity decrease? Note: Remember that a decrease of 10 dB means that we perceive this sound half as loud.
Two example graphs show the sound intensity of a buzzer placed inside of a sealed glass flask. The graph has a maximum value recorded of 68 decibels, an average value of 42 decibels and a minimum value of 28 decibels. The sound intensity starts high and gradually decreases throughout the graph. A marker is placed on the left graph at the start of the experiment and another marker is placed on the right graph at the end of the experiment.
Figure 7. This example data from the phyphox app demonstrates how to determine the sound intensity of the buzzer at the beginning and end of the experiment. The x-axes of the graphs are time in seconds [s] and the y-axes shows sound intensity in decibels [dB].
- Repeat the analysis with all the graphs from each of your trials. Did you see similar results every time? What could be the reasons for any differences?
- What do your results tell you about sound in outer space where there is a vacuum? Do you expect any sounds to be heard there? Why, or why not?
Ask an Expert
- What happens if you put the flask into an ice bucket (use crushed ice) after replacing the stopper and bell? Caution: as noted in the Materials and Equipment section, be sure that your flask is made of borosilicate glass, which will not shatter when subjected to rapid changes in temperature .
- Find a way to compare sounds of different objects in air versus water. Which medium (air or water) is better in transmitting sounds?
- Investigate what happens if you let the battery or buzzer touch the glass at the inside of the flask when putting the rubber stopper in. What happens if you have a physical connection between the sound generator (buzzer) and the flask? Will the vacuum still reduce the buzzer's sound intensity? Why or why not?
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