Cosmic Horizons

I love this video and used to do this very demo when teaching classical mechanics. But here's a question for you - why doesn't the wheel fall over? If you trawl the text books, even the wonderful Feynman Lectures on Physics (a must read for any serious student of physics), the answer given is that the wheel doesn't fall down because of the conservation of angular momentum . Alas, I think this answer is a bit of a cop out, and doesn't answer the question. Why? Let's consider the collision between two cars. We know from Newtonian mechanics that momentum is conserved, so the momentum before the collision is exactly the same as after the collision (let's ignore external forces for now, imagine the collision is on a frictionless sheet of ice). The conservation of momentum is a consequence of Newton's third law, and in the collision all of the forces acting have equal and opposite reaction forces, with the total momentum unchanged. Basically, conside

For a long time, I have been a fan of David Bowie , and have seen him in concert a couple of times. In the good old days (early 1980s), when MTV showed nothing but music videos, I would happily while away the hours on Bowie (and Queen, and just about everything else). But as everyone knows, people grow-up and have to go to university, and MTV went the way of pathetic shows rather than showing videos, and so I didn't really watch music videos any more. While holidaying last week, we happened to be chilling, and decided to watch a bit of Rage as they were showing a series of Bowie videos, and while watching Let's Dance , I had a "ehh - that's familiar" kind of moment. It was driven by this image a sight what will be familiar to astronomers the world over. No, not the people in the foreground, or the nuclear explosion in the background, but the mountains! Why? Because they are the mighty Warrumbungles , mountains in Northern(ish) New South Wales, near the

Sorry for the delay, but I've been off on a family holiday, touring and camping in New South Wales (which doesn't look a lot like the old version), coupled with a trip over the border into alien territory, namely Queensland. I was on the Gold Coast , a tourist mecca and home to a number of theme parks. As the father of little-cusps, we headed to DreamWorld to be thrown about a little. When I was riding the Cyclone.... I remember a post a long time ago by my ex-Honours and MSc student, Luke Barnes (who has just returned to an Australia as a Super Science Fellow), namely what does it feel like to be weightless. Of course, what I mean by weightless is something like this, namely some astronauts cavorting about in orbit, floating about and just having a good old time of it. So, what does weightlessness *feel* like? Many have seen astronauts training, in their gear, in water tanks. They can bob about and look something like this Doesn't that look nice and peacefu