This morning I listened to the May 14th broadcast. One of the discussions was about the stinging cells (nematocysts) of jelly fish. Someone brought up the point about the ability of certain species to incorporate these stingers into their own tissue and this is a subject I know a little bit about.

I understand the basic idea that for every action there is a reaction, which is why I can walk across the ground. But when a rocket is in space and they decide that they want to change the direction of the rocket or slow it down, what's the engine firing against? What's it pushing against to slow the rocket down, because we're told that in space, there's nothing there?

Please can you calculate how much extra fuel will be burned by a motorist during the current World Cup campaign as a result of flying flags from vehicles, bearing in mind the increased drag.

What happens to the great hollows that we're leaving below the sea beds when you extract all this oil and gas?

I've been following the progress of solar panels and hear that they're only about 16% efficient. What's the score with this?