Capturing the speed of sound and speed of light on video.

In summary: When you take a picture with a flash, the camera actually takes multiple frames per second, but the image you see on the camera screen is only displayed once per second. So, if you stop the footage at a frame where the light beam is hitting the person's eyes, they would see the light coming towards them even if it was a fraction of a second after the light actually hit their eyes.
  • #1
n0sferatu
4
0
Hi!

Consider a high-speed camera set up to record an explosion and the resulting shockwave emanating from the explosion. In the same frame you can see the shock wave as well as people in the distance. Is it true that the people in the distance wouldn't hear the sound of the explosion until the visible wave in the video hits their eardrums? That is, is the pressure wave that emanates from the explosion and that is captured in the video the same as the sound waves that the person hears?

Next, consider the same setup except using a flash light that is aimed at a person's eyes. Could there ever be a camera developed that can record frames faster than the speed that light travels? If so, could you then play back the video and actually see the beam of light traveling in slow-motion through space towards the persons eyes? Also, if you stopped at a frame in the middle of the footage (with the light beam 1/2 way from the source to the persons eyes), would the person not realize that the flash light was on at that exact moment because the photons of the light beam hadn't hit their retinas yet?

Just curious! Thanks!
 
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  • #2
n0sferatu said:
Hi!
Welcome to PF!
Consider a high-speed camera set up to record an explosion and the resulting shockwave emanating from the explosion. In the same frame you can see the shock wave as well as people in the distance. Is it true that the people in the distance wouldn't hear the sound of the explosion until the visible wave in the video hits their eardrums? That is, is the pressure wave that emanates from the explosion and that is captured in the video the same as the sound waves that the person hears?
Correct. Example:

A few tidbits about this:
1. You can see the shock wave in air kicking up dust as it races across the desert.
2. The speed of sound in Earth is much higher than in air, so before the air shockwave and sound hit you, the ground starts rumbling under your feet.
3. For dramatic effect, the TV station synced the sound to the explosion. What actually happens is you hear nothing when you first see the explosion, then the ground starts to shake under you, then the shock wave hits you. I recently saw a Mythbusters clip where they describe this - I'll have to look for it.
Next, consider the same setup except using a flash light that is aimed at a person's eyes. Could there ever be a camera developed that can record frames faster than the speed that light travels?
That doesn't make sense. Cameras record in frames per second - that's a rate, but not a speed. Speed is meters per second.
If so, could you then play back the video and actually see the beam of light traveling in slow-motion through space towards the persons eyes?
The only light you can see is light that hits your eyes. It is however, theoretically possible to set up perpendicular to a laser and watch the beam extend from its source when turned-on. The beam is visible because dust in the air reflects some of the light away from the path of the laser and into the camer/your eyes.
Also, if you stopped at a frame in the middle of the footage (with the light beam 1/2 way from the source to the persons eyes), would the person not realize that the flash light was on at that exact moment because the photons of the light beam hadn't hit their retinas yet?
With the setup I described above, you could witness something like that. Note, however, you'd need a baseline of a hundred thousand km for the experiment to show that effect on a human timescale. Human reaction time is on the order of 1/10 of a second.
 
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  • #3
n0sferatu said:
Next, consider the same setup except using a flash light that is aimed at a person's eyes. Could there ever be a camera developed that can record frames faster than the speed that light travels? If so, could you then play back the video and actually see the beam of light traveling in slow-motion through space towards the persons eyes? Also, if you stopped at a frame in the middle of the footage (with the light beam 1/2 way from the source to the persons eyes), would the person not realize that the flash light was on at that exact moment because the photons of the light beam hadn't hit their retinas yet?

Pretty much this exact phenomenon is observed in astronomy: http://en.wikipedia.org/wiki/Light_echo
 
  • #4
n0sferatu said:
Next, consider the same setup except using a flash light that is aimed at a person's eyes. Could there ever be a camera developed that can record frames faster than the speed that light travels? If so, could you then play back the video and actually see the beam of light traveling in slow-motion through space towards the persons eyes?

AFAIK, streak cameras are used (essentially) for this purpose- they are used for tracking short pulses.

http://www.optronis.com/support/streak-kameras.html
http://sales.hamamatsu.com/en/products/system-division/ultra-fast/streak-systems.php
http://sales.hamamatsu.com/assets/pdf/catsandguides/e_streakh.pdf
 
  • #5
Thanks for the replies and very interesting links, I appreciate it!
 

What is the speed of sound and how is it captured on video?

The speed of sound is the rate at which sound waves travel through a medium, typically air. It is approximately 343 meters per second in dry air at room temperature. To capture the speed of sound on video, a high-speed camera is used to record the movement of an object that is producing sound waves. The distance between frames can then be measured to calculate the speed of sound.

How does the speed of light compare to the speed of sound, and can it be captured on video?

The speed of light is much faster than the speed of sound, traveling at approximately 299,792,458 meters per second. This makes it difficult to capture on video. However, with specialized equipment and techniques, it is possible to record the movement of light waves and calculate their speed. This is often done in experiments and demonstrations in physics and optics.

What factors can affect the accuracy of capturing the speed of sound and speed of light on video?

Several factors can affect the accuracy of capturing the speed of sound and light on video. These include the quality and frame rate of the camera, the distance between the camera and the object, and any obstructions or interference in the medium through which the sound or light is traveling. It is important to consider and control for these factors when attempting to capture these speeds on video.

In what real-world applications is capturing the speed of sound and speed of light on video useful?

Capturing the speed of sound and light on video has many practical applications. In research and development, it can help scientists and engineers better understand the behavior of sound and light waves and how they interact with different materials. It can also be used in educational settings to demonstrate and explain concepts related to the speed of sound and light. Additionally, high-speed videos of sound and light can be used in artistic and creative projects to produce visually stunning effects.

What advancements have been made in technology to improve the accuracy and ease of capturing the speed of sound and speed of light on video?

With the advancement of technology, there have been significant improvements in the accuracy and ease of capturing the speed of sound and light on video. High-speed cameras with faster frame rates and higher resolutions are now available, allowing for more precise measurements. Additionally, software and algorithms have been developed to analyze the captured footage and calculate the speed of sound and light more efficiently. These advancements have made it possible to capture and study these speeds in more detail than ever before.

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