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MCAT
Course: MCAT > Unit 8
Lesson 15: Sound- Sound questions
- Sound is a longitudinal wave
- Production of sound
- Sound Properties: Amplitude, period, frequency, wavelength
- Speed of Sound
- Relative speed of sound in solids, liquids, and gases
- Decibel Scale
- Why do sounds get softer?
- Ultrasound medical imaging
- Standing waves in open tubes
- Standing waves in closed tubes
- Doppler effect introduction
- Doppler effect formula for observed frequency
- Doppler effect formula when source is moving away
- When the source and the wave move at the same velocity
- Doppler effect for a moving observer
- Doppler effect: reflection off a moving object
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Speed of Sound
How fast does sound travel? Explore the nature of sound waves and how they travel. Discover why sound is a longitudinal wave and how its speed is influenced by the medium it travels through. Learn about the relationship between wavelength, frequency, and speed, and how changing the medium affects the speed of sound. Created by David SantoPietro.
Want to join the conversation?
How can the amplitude be changed?(7 votes)
Once the wave has started, you can only dampen the sound (reduce the amplitude), and this happens naturally because sound energy is lost in transmission, for the same reason you cannot hear people whispering when they are very far away. If you wanted to increase it, you would need to add additional energy at the start but you cannot make something louder once the sound wave has started(14 votes)
Does increasing amplitude change the frequency or wavelength of a wave?(4 votes)- No, the amplitude is how loud something is, and you can increase the height of a wave without influencing the length of each wave.
Similarly, the frequency or wavelength determines the pitch (how high a note is) and you can play different pitches at the same volume.(10 votes)
Does speed of sound in a gas increase with pressure?Why or why not?(4 votes)
Yes, because speed of sound is dependent on the medium's density. As you apply more pressure to a compressible medium (gas works here!) the medium is compacted into a smaller space, and have many more interactions with the other molecules. If you're a sound wave, this is your bread and butter because you rely on intra-medium interactions, so to speak. Sound propagates because of compressions and transfers of energy through a medium.
This is why sound is so much faster under water (and why the speed under water in the ocean is so variable due to different densities because of different salinities and temperatures).(7 votes)
So what exactly is going on when you speed up or slow down a video on YouTube, for example? It seems the pitch goes up if you speed up the settings (higher frequency), but does that mean the speed of sound is still unchanged and it's all due to a change in wavelength?(5 votes)
Yes, speed of sound relies only on the medium it is traveling through. The higher pitch is due to the shorter wavelength, and, therefore, higher frequency.(5 votes)
If you change the speed of the sound will the frequency change and why(3 votes)
The frequency would not be impacted. Frequency is determined by the frequency of the source, and the properties of the medium (stiffness and density) determine the speed of sound. The wavelength would change however since λ = c/f where c is the speed of sound.(5 votes)
can sound and light travel in vacum? why?(0 votes)
no,sound cannot travel through vacum because -
vacum is a place with no air n there will be no matter for the vibrations to work in but light can travel through vacum as light is a electro-magnetic wave n it is produced when there is a disturbance in the electro magnetic field n a electro magnetic field is present in the vaccum.(9 votes)
Helium was used as an example here for changing the speed of sound. Why helium?(2 votes)- Helium atoms are much lighter than oxygen and nitrogen molecules, so the speed of sound is greater (by about a factor of 3). It's like putting a lighter mass on a spring: it will oscillate at a higher frequency.(3 votes)
- If I stand at a distance where when the person speaks slowly is not audible, why then if the person speaks louder in the same distance is audible(2 votes)
As the air molecules moves they experience Friction ,Therefore at some distance it stops and doesn't reach our ear drum . So because no vibration in our eardrum , we doesn't hear any sound . But when we speak louder because of more disturbance in air molecule it stays in chain for long range and easily overcome friction. It also depends where you are speaking , in a very empty room or a room filled with sound absorbing materials.(3 votes)
- Is there any differences between the graph of Transverse waves and the graph of Longitudinal waves?(3 votes)
- In a Transverse waves the particles in a medium vibrate up and down. They consist regions of crests and Through. They are perpendicular to each other.
Example: Ripples produced on the water of a pond.
In Longitudinal waves the particles in a medium vibrate to and fro in the same direction in which the wave is moving. They are Parallel to each other. They consists region of compression and refraction.
Example: Sound waves.👍(2 votes)
To find the speed of the sound why do we calculate the distance on one wave length and divide it by the time taken. So why those the sound amplitude decreases as it travel's and we hear a sound with less frequency(2 votes)
Video transcript
- If we let a speaker
make one short burst, we'll create a pulse wave. We can find the speed of sound by looking at the speed
of this compressed region as it travels through the medium. In non-humid air at 20 degrees Celsius, the speed of sound is about 343 meters per second
or 767 miles per hour. We can also watch the speed of sound of a repeating simple harmonic wave. The speed of the wave
can again be determined by the speed of the compressed regions as they travel through the medium. Note that the speed of sound does not mean the speed of the air molecules
as they move back and forth. The air molecules are
moving with the speed, but by the speed of sound, we mean the speed of the disturbance as it moves through the air molecules. We call sound a longitudinal wave because the wave is traveling parallel to the line traced out by the
oscillations of the medium. The other type of wave
is a transverse wave. Transverse waves happen
when the wave velocity points perpendicular to the
oscillations of the medium. Waves on a string or waves
on the surface of water are examples of transverse waves. If we look at a graph
of the air displacement versus position of the air, we can see that as the wave travels the shape of this wave
travels to the right. So, the speed of a sound wave can be found by finding the speed of the peaks or the speed of the valleys or the speed of any single
point on the wave shape. To figure out a formula for
the velocity of a sound wave, let's look closely at
what's happening here. Watch one of the air molecules. It takes one period for this molecule to move back and forth
through a full cycle. During this time, the wave
shape has moved forward one complete wavelength. This is because the wave has to overlap with its initial shape after one period, because the molecule has
to be back where it started after one period. Now, since speed is defined
to be the distance per time, the speed of a sound wave has to be the wavelength of the wave divided by the period of the wave. Since the wave is traveling forwards one wavelength per period, or since the frequency is defined
to be one over the period, we can rewrite this formula as speed equals wavelength times frequency. This formula is accurate
for all kinds of waves, not just sound waves, because a wave has to move one
wavelength for every period. Be careful. When looking at this equation, you might think that if you adjust the setting on your speaker
and increase the frequency you'd also be increasing
the speed of the sound wave, but that's not what happens. If you increase the frequency, the wavelength will decrease
by that same factor, and the speed of the sound
wave will remain the same. In fact, there's nothing
you can do to the speaker that would increase the speed of sound. So, how can we change the speed of sound? Well, the only way to
change the speed of sound is to change the medium or
the properties of the medium that the sound wave is traveling in. So, to change the speed of sound in air, you can change things like
the temperature of the air or the humidity of the air
or the density of the air, or you can swap out the air
entirely for another material, like water or helium or a metal. All of these changes to the medium would affect the speed of sound. People often think that
changing the amplitude will change the speed of a
sound wave, but it won't. If we create a sound pulse
with a large amplitude, it won't travel any
faster than a sound pulse with a small amplitude in the same medium. It will just be louder. In other words, yelling won't cause
anyone to hear you faster, they'll just hear a louder sound when the sound wave
arrives at their location. So remember, the speed of a sound wave is determined entirely by
the properties of the medium through which it's traveling.