Chris Smith: Hello and welcome to the Naked Scientists: Up All Night which is produced in association with the Open University. I'm Chris Smith. In this week’s show, why scientists might have to rewrite the history books of human origins because our ancient relatives, it turns out, might not have looked the way that we first thought they did. And as Bond mania takes hold of cinemas across the World, we'll also be unpicking the workings of the silencer to find out whether they really can do what Hollywood would have you believe.
Hugh Hunt: When the bullet leaves the end of the barrel, the pressurised gas suddenly expands, and that’s what makes the noise. And it's just like it with a balloon. If I take a balloon, I’ve got a balloon here, and if I pop it, it sounds like this [balloon pops]. Okay. It makes a big noise because the gas inside the balloon is suddenly being released.
Chris Smith: Hugh Hunt will be investigating the workings of the assassin’s silencer. That’s all on the way in this week’s Naked Scientists: Up All Night.... You’re listening to the Naked Scientists: Up All Night with me Chris Smith and time now for this week’s Stuff and Non-Science where we massacre myths and bash bad science and hopefully nowhere a firing range, here’s Diana O’Carroll.
Diana O’Carroll: This week’s Stuff and Non-Science is the myth told by movies on gun silencers. Are they really as easy to use and effective as we’re told? Here’s Hugh Hunt to explain.
Hugh Hunt: Well you’re never going to get a gun to be completely quiet. Probably a better name for a silencer would be a muffler because it reduces the noise rather than to eliminate the noise. But the first thing we need to do is think about what the sources of the noise are. In a gun, there are three main sources. The first thing is that the gas, the hot high pressured gas that propels the bullet along the barrel, has to be released at some stage. And when the bullet leaves the end of the barrel, the pressurised gas suddenly expands, and that’s what makes the noise. And it's just it like with a balloon.
If I take a balloon, I’ve got a balloon here, and if I pop it, it sounds like this [balloons pops]. Okay. It makes a big noise because the gas inside the balloon is suddenly being released. But if I take another balloon and this time just blow it up, and now I'm going to release the pressure gently [balloon deflating]. Now it's a lot lot quieter. That’s because the high pressure air is released at a slower rate. Now that’s essentially what the silencer or the suppressor does. It gives the high pressure gas space to expand slowly as the bullet leaves the end of the barrel.
Now let’s suppose we've got a really good silencer, and we've got two other noise sources. The first is that the bullet leaves the barrel supersonic, and we get a sonic boom just like with a high speed aircraft. If we wanted to get rid of the sonic boom, well we simply have to slow that bullet down to be subsonic, and maybe the silencer can be designed to achieve that. Now then there’s a third noise which actually you’re only beginning to hear once you’ve got rid of all the other noises, and that’s the click of the trigger mechanism. Now you could imagine James Bond, he goes to fire his gun, and the gun’s not loaded, but what you hear is something like this [click]. Well, it's quite a loud noise, but it's not as loud as the bang from the explosive charge or from the supersonic bullet. Once you’ve got rid of the other two noises, then it does become significant.
Now silencers are most commonly used by hunters say in Alaska, they’re out hunting deer. Really they just want to be not making quite as much noise as they might if they didn’t have a silencer, and maybe it means they don’t have to wear hearing protection when they’re using their guns. But your bog standard silencer is still going to leave you with a gun which is pretty noisy.
Diana O’Carroll: That’s Hugh Hunt, Senior Lecturer in Engineering at Cambridge. That’s it for this week’s Stuff and Non-Science, but if you have a bit of science knowledge you don’t believe in then send it to me email@example.com.
Chris Smith: So some practical tips for Sarah Palin there next time she’s out hunting for moose in Alaska - thank you Diana. That’s Diana O’Carroll with this week’s Stuff and Non-Science.
Well, that’s it for this time. We’re back next week with another round up of the latest findings from the world of science. The Naked Scientists: Up All Night is produced in association with the Open University, and you can follow up on any of the items that you heard in the programme via the OU’s website, that’s at open2.net/nakedscientists or, alternatively, you can follow the links to get there from the BBC Radio Five Live Up All Night External link 6 website.
The production this week was by Diana O’Carroll from the nakedscientists.com, and I'm Chris Smith. Until next time, goodbye!