But why is the speed of sound greater in a solid than in air? Here is my super-short answer. Sound is a moving disturbance in a medium. In air, some particles interact with nearby particles, causing them to move. Then these moving particles push other particles, and so on. The same thing happens in a solid, but with one big differencedensity. Since the density of a solid is so much higher than a gas, the distance between particles is much smaller.
This allows the disturbance to propagate faster and makes the speed of sound higher. One more thing. The plan is to take a long section of flat glass and crack it on one end. After that, it's just a matter of looking at the propagation of the crack with the high-speed camera. They also marked off 1 foot sections in the glass so that they could get some time measurements. For their first attempt, they used a camera speed of 28, frames per second I think that's what he said.
Although they didn't find the cracking speed from this run, I am going to do it for them. Using video analysis, I can get the position of the leading edge of the crack in each frame of the video. It's not too hard to do this.
Using Tracker Video Analysis , I can set the scale of the video using the 6 feet of visible glass and then mark the location. Oh, don't forget to change the frame rate in the video. Here is the plot of the position of the leading edge of the crack as a function of time. That means the Slow Mo Guys were a bit too slow—they recorded with a measly 28, frames per second.
The Slow Mo Guys calculated crack propagation speed as 1, meters per second 4, The Slow Mo Guys reported crack propagation speed as 1, meters per second 4, You could calculate the speed for yourself, or you could check out this Wired article by Southeastern Louisiana University professor Rhett Allain. Hang on, though. For glass, the speed of sound is about 4 to 5 kilometers per second , but the Slow Mo Guys recorded crack propagation speed at just under 1.
No reproduction without expressed written permission. Contact info glass. My brother has a car that has a really bad windshield.
It would be nice for him to get a professional to fix it. How long can it take for a crack to start once a rock has hit the windshield? Does it happen right away or what is the longest time period you are aware of…from strike to start of crack. Great question! A crack can form right away or it might take years.
It depends on a number of factors such as weather, how the vehicle is used, and the severity of the original damage. Thank you. I heard nothing while I drove it miles and then parked it for a couple days before I noticed the crack. Is it possible to get hit by a rock and not hear it? I have had been hit by a rock in my personal car and the noise was VERY startling. It was similar to a gun shot. My stance with the rental company is that there could have been a chip that they did not notice and I did not notice before leaving the lot and it just so happened to crack during my watch.
Needless to say, next time I rent a car I will run my hand over the windshield to check for chips and note anything remotely like a chip.
Bugs included. They could be covering up a chip.
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