Speed of Sound and Mac

In summary, the producer wants to save money by shooting a boat chase scene with boats going at 1/4 the speed seen on film and quadrupling the speed of playback. This may not work due to the change in frequency of the sounds heard, which is dependent on the speed of sound and the temperature.
  • #1
Idioticsmartie
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Speed of Sound and Mach

Homework Statement


You are hired as the physics consultant for a large movie studio. The producer is way over budget and wants to perform some special effects that will save him money. He decides to shoot the dramatic action boat chase scene with the boats going at 1/4 the speed of what will be seen on film. He quadruples the speed of playback. Explain why or why not this will work.


Homework Equations



Mach # = velocity of boat/ speed of sound
Speed of sound = 331 + 0.60*T
T = temperature


The Attempt at a Solution



I don't even know where to begin. I don't think it will work, but maybe if someone could point me in the right direction?
 
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  • #2
I think the idea is that the sound won't be right. What happens to the frequency of the sounds heard when playback is quadrupled?
 
  • #3


As a physics consultant for the movie studio, it is my responsibility to ensure that all special effects are both scientifically accurate and visually appealing. In this case, the producer's idea of shooting the boat chase scene at a slower speed and then quadrupling the playback speed may seem like a cost-saving measure, but it is not a feasible solution.

Firstly, let's consider the concept of Mach number, which is the ratio of an object's speed to the speed of sound. In this scenario, the boats are moving at 1/4 the speed of what will be seen on film, which means their Mach number is 0.25. However, when the playback speed is quadrupled, the boats will appear to be moving at 4 times their actual speed, giving them a Mach number of 1. This is well above the speed of sound, which can cause significant issues.

When an object travels at or above the speed of sound, it creates a shock wave known as a sonic boom. This can be extremely loud and can even cause damage to nearby structures. In the case of the boat chase scene, the boats appearing to move at a Mach 1 speed would create a deafening sonic boom, which would not only be unrealistic but also potentially dangerous for the actors and crew on set.

Furthermore, the speed of sound is affected by temperature, as shown in the equation provided. This means that if the temperature on the day of filming is different from the temperature when the playback speed was quadrupled, the boats would appear to be moving at a different speed than intended. This would result in an inconsistent and inaccurate portrayal of the boat chase scene.

In conclusion, while the producer's idea may seem like a cost-saving measure, it is not a scientifically accurate or safe solution for the boat chase scene. It is important to adhere to the laws of physics and ensure that all special effects are realistic and safe for everyone involved.
 

1. What is the speed of sound?

The speed of sound is the rate at which sound waves travel through a medium. In dry air at 20°C, the speed of sound is approximately 343 meters per second.

2. How does temperature affect the speed of sound?

The speed of sound is directly proportional to temperature. As the temperature of a medium increases, so does the speed of sound. This is due to the increase in molecular motion and collisions, allowing sound waves to travel faster.

3. What factors can affect the speed of sound in a medium?

The speed of sound can be affected by temperature, humidity, and the density and compressibility of the medium. For example, sound travels faster in warmer, less dense air than in colder, denser air.

4. How is the speed of sound measured?

The speed of sound can be measured using a variety of methods, including the time-of-flight method, resonance method, and Doppler effect. These methods involve measuring the time it takes for a sound wave to travel a known distance or using the change in frequency of a sound wave as it moves toward or away from an observer.

5. What is the relationship between speed of sound and the Mac number?

The Mac number, also known as the Mach number, is a unitless number that represents the ratio of an object's speed to the speed of sound in the medium it is traveling through. When an object travels at the speed of sound, its Mac number is 1. As the speed of the object increases, the Mac number also increases. This relationship is important in understanding and predicting phenomena such as shock waves and supersonic flight.

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