Sea anemones, which also possess nematocysts, are the primary food of Nudibranchs (sea slugs) in my geographic area. The nudibranchs will feed on the anemone and some of the nematocysts survive unfired to be transported to Cerata. The cerata are similar to the tentacles of the anemone and lie on the dorsal surface of the slug. I used to examine these cerata and the incorporated nematocysts using an electron microscope many years ago. It's really quite fascinating to follow the progression from the digestive tract into the cerata. I don't have a clue how they accomplish this. Anyway, if anyone is interested in more information, the two species I know of are called Aeolidia papillosa and Coryphella rufibranchialis. You should be able to find some info about these creatures on the web.

A rocket works by throwing something out of the back so the rocket goes forward. So the action and reaction are actually inside the spacecraft. The fuel pushes outwards and pushes the spacecraft forwards. So in space what we actually use is a fuel called hydrazine and we burn this out of the back of the spacecraft through little thrusters. This is how we manoeuvre the spacecraft and push it around. There are some other ways we do it as well. We're looking at things such as ion drives. That takes individual atoms, ionises them so that they've got an electric charge, and then uses electric fields to throw these gas molecules out f the back of the spacecraft. We've used that sort of application to send a spacecraft to the moon. It took a long time to get there but was moving very fast by the time it got there. So that could be a possibility for long range spacecraft. The bottom line is that if you want to slow something down you have to apply force in the opposite direction to which you're travelling. So you have these retro-rockets which fire against the direction in which you're travelling. So the rocket has a certain momentum moving in one direction and you want to give it momentum in the other direction so they cancel each other out. So the rocket is pushing against itself.

No comment! They scare horses as well apparently!

First of all, when the oil is extracted, it's coming out of the pores in the sandy rocks and in most places the framework of that rock remains reasonably intact. You do in the long term get some subsidence. Perhaps the most notorious example is in the Netherlands where they don't really want anymore sinking but there's a very large gas field in the middle of the Netherlands called the Groningen gas field. There's a lot of subsidence associated with that. There's also a lot of subsidence associated with coal fields but that's a little bit different because you're excavating underground. When the oil comes out it's seeping out of the pores, so you're not actually making a big hole down there.

They are only about 15% efficient. The best ones yet are in the order of about 30%. There's new research going into this now where people are working out a way of making them spit out far more electrons, or current, for one photon or particle of light. But it's certainly experimental at the moment and the thing is that they're so expensive to build and environmentally costly to build that it's not like Peter's ramp. It's actually costing you far more to build them and run them at the moment than they actually ever pay back, so it's just not energy efficient.