Calculate Speed of Sound
5 هزار بار بازدید -
4 سال پیش
-
Sound, a form of energy,
Sound, a form of energy, is all about vibrations.
We hear it as it travels in air from its source to our ears.
Lightning and thunder are produced simultaneously, but the thunder is heard a few seconds after the lightning is seen.
Same is true with the sound of a bat hitting the ball.
This is because the speed of light is much more than speed of sound.
The natural vibrations of the air in the flute are due to a phenomenon called resonance.
We will take help of this effect to calculate speed of sound.
To calculate the speed of the car, we need distance the car has travelled in a given time.
We will calculate the speed of sound in air with the help of two terms associated with it - wavelength and frequency.
Instead of using tuning forks with known frequency, we will use an app on our mobile phone. - Frequency Generator. This is how 900 Hz sounds.
We will use this PVC pipe to calculate the wavelength of this sound.
This PVC pipe open at both ends. Let us fill this glass with water.
With 900 Hz sound from the phone placed near the open end, we will lower the pipe inside water.
Height of the open air column inside changes as we move the pipe up and down.
At one particular location, sound becomes louder. This is the length of the air column which resonates with the 900 Hz source of sound.
It is 88 mm or 8.8 cm.
Let us do some analysis.
This end of the pipe is closed while the other end is open.
Air particles inside the pipe are moving randomly. Sound from the speaker causes air particles to vibrate. Sound particles oscillate without leaving their location as sound travels. This is just one pressure pulse from the speaker. It travels and bounces back at the close end. As the frequency of this sound is 900 Hz, this happens 900 times in a second.
Incoming and reflected pulses results in a standing wave pattern which I will not go into detail right now.
X axis represents distance from the closed end.
Inside the pipe, Pressure at the closed end is highest while it is approximately equal to atmospheric pressure near the open end.
This results in no displacement or movement of air particles near the closed end while maximum displacement of air particles near the open end. This is shown as a red line.
If we plot the graph of this movement, it will look something like this.
The part inside the pipe is one fourth of the wavelength of sound.
In our case it is 88 millimeter.
Maximum displacement happens slightly outside the pipe. We have to add some value to this which is called end correction.
It is equal to 0.3 times diameter of the pipe. 0.3 x 16 mm = 4.8 mm
88 + 4.8 = 92.8 milimeter.
9.28 centimeter.
Wavelength of this sound is four times 9.28 centimeter that is 37.12 centimeter.
Which is 0.3712 meters.
We will multiply this with 900 to get the speed of sound .
334 meter/second.
Sound also depends on the temperature. With 28 degree Celcius,
This is close to the calculated speed of sound at 348 meter / second.
Many scientists have doubted the formula for end correction.
We will try another way to calculate the speed of sound which does not need end correction.
If we take the same pipe with 30 length and repeat the activity, we can hear resonance at two places.
This length is marked as l1 while this one is marked as l2.
We can combine these two equations to get rid of end correction.
First at 28 cm and next at 8.8 cm.
As per the formula , we can calculate the speed of light as 345.6 meters per second which is very close to the actual speed of sound at this temperature.
Now that you know how to calculate speed of sound, do try with these variations in terms of shape and size of the resonating object as well as that of the water container.
With the help of a plunger tip of the syringe and pencil, you can also do this activity without using water. Do give it a try !
Thank you.
We hear it as it travels in air from its source to our ears.
Lightning and thunder are produced simultaneously, but the thunder is heard a few seconds after the lightning is seen.
Same is true with the sound of a bat hitting the ball.
This is because the speed of light is much more than speed of sound.
The natural vibrations of the air in the flute are due to a phenomenon called resonance.
We will take help of this effect to calculate speed of sound.
To calculate the speed of the car, we need distance the car has travelled in a given time.
We will calculate the speed of sound in air with the help of two terms associated with it - wavelength and frequency.
Instead of using tuning forks with known frequency, we will use an app on our mobile phone. - Frequency Generator. This is how 900 Hz sounds.
We will use this PVC pipe to calculate the wavelength of this sound.
This PVC pipe open at both ends. Let us fill this glass with water.
With 900 Hz sound from the phone placed near the open end, we will lower the pipe inside water.
Height of the open air column inside changes as we move the pipe up and down.
At one particular location, sound becomes louder. This is the length of the air column which resonates with the 900 Hz source of sound.
It is 88 mm or 8.8 cm.
Let us do some analysis.
This end of the pipe is closed while the other end is open.
Air particles inside the pipe are moving randomly. Sound from the speaker causes air particles to vibrate. Sound particles oscillate without leaving their location as sound travels. This is just one pressure pulse from the speaker. It travels and bounces back at the close end. As the frequency of this sound is 900 Hz, this happens 900 times in a second.
Incoming and reflected pulses results in a standing wave pattern which I will not go into detail right now.
X axis represents distance from the closed end.
Inside the pipe, Pressure at the closed end is highest while it is approximately equal to atmospheric pressure near the open end.
This results in no displacement or movement of air particles near the closed end while maximum displacement of air particles near the open end. This is shown as a red line.
If we plot the graph of this movement, it will look something like this.
The part inside the pipe is one fourth of the wavelength of sound.
In our case it is 88 millimeter.
Maximum displacement happens slightly outside the pipe. We have to add some value to this which is called end correction.
It is equal to 0.3 times diameter of the pipe. 0.3 x 16 mm = 4.8 mm
88 + 4.8 = 92.8 milimeter.
9.28 centimeter.
Wavelength of this sound is four times 9.28 centimeter that is 37.12 centimeter.
Which is 0.3712 meters.
We will multiply this with 900 to get the speed of sound .
334 meter/second.
Sound also depends on the temperature. With 28 degree Celcius,
This is close to the calculated speed of sound at 348 meter / second.
Many scientists have doubted the formula for end correction.
We will try another way to calculate the speed of sound which does not need end correction.
If we take the same pipe with 30 length and repeat the activity, we can hear resonance at two places.
This length is marked as l1 while this one is marked as l2.
We can combine these two equations to get rid of end correction.
First at 28 cm and next at 8.8 cm.
As per the formula , we can calculate the speed of light as 345.6 meters per second which is very close to the actual speed of sound at this temperature.
Now that you know how to calculate speed of sound, do try with these variations in terms of shape and size of the resonating object as well as that of the water container.
With the help of a plunger tip of the syringe and pencil, you can also do this activity without using water. Do give it a try !
Thank you.
4 سال پیش
در تاریخ 1399/06/15 منتشر شده
است.
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