# Sound130

OP43 recall that the speed of sound is less than the speed of light

OP44 explain the time lag between seeing and hearing the same event.

The speed of light 299,800,000 m/s and the speed of sound is about 350 m/s, so the Speed of light is 856,700 time faster than the speed of sound. This means it take longer for the sound to travel through air than it does the light. For a 4km distance between explosion and the observer, takes 0.0000133 seconds for light to travel and about 12 seconds for the sound to travel.

so from this we can calculate the Distance to be = speed x time ....

330 x 12 = almost 4 km!

If you want to measure the speed of sound follow these instructions

Speed of Sound in Air - Bang and Time Method

Posted in Physics by esf science on April 1, 2009

Apparatus

Method

1. Find a field with a wall, or a tall, wide building at one end of it. The school car park will work fine - there’s a brick wall at the North end which reflects the sound back to the experimenters very well.

2. Pace out 100m from the wall. You might be in the tennis courts.

3. Bang two wooden blocks together sharply and listen for the echo. It sounds like the crack of a cricket ball being struck.

4. Bang the blocks together again at exactly the same time as you hear the echo, You might have to practise this to get it exactly right.

5. Start a stopwatch and time how many bangs you make in one minute.

6. Repeat twice more and average for accuracy.

Thanks to the Tang-Pedersen twins for their help.

Calculation

• Number of bangs in 60s = 96 (average of 3 times)

• Time for the sound to travel there and back once = 60/96 s =o.625s

• Distance travelled by the sound waves there and back = 2 x 100m

• Given that : Speed = distance/time, the speed of sound in air = 200m/0.625s = 320m/s.

The actual value is closer to 343 m/s or 1236 km/h, which increases with increasing temperature.

The breaking of the sound barrier.

http://en.wikipedia.org/wiki/File:FA-18_Hornet_breaking_sound_barrier_(7_July_1999)_-_filtered.jpg

"Due to the difference in the speed of light and sound, you see it go up, then you hear this amazing, crackling, thundering noise a few seconds later. It’s amazing. Lots of people try and video it, but NASA’s advice is just to experience it."

- Journalist and space lecturer Ruth McAvinia on what a shuttle launch is like