Archive for demonstration

How big was the 23rd March Put It To The Vote march? A: too big to ignore

Posted in Uncategorized with tags , , , , on March 25, 2019 by telescoper

This post offers some interesting reflections on Saturday’s march. I recall the anti-War march in 2003 and would say that Saturday’s was similar in size, and both were substantially larger than the one last autumn.

I heard the organisers announce an official estimate of 1 million (without an error bar). Not being able to reach the end of the march – barely got halfway – I can’t make a quantitative estimate. I’ll just say that if someone told me it was two or three times as big as the one in 2018 then I wouldn’t be surprised.

I’ll just add that it was very enjoyable and the participants were very friendly and polite – so different from the abusive and threatening conduct of the other side. That is probably the Remainers’ biggest problem – we’re just too nice. The government is far more likely to be swayed by threats of `blood on the streets’ than civilized peaceful protest, which is why I fear so much for the direction in which the UK is heading.

Kmflett's Blog

How big was the 23rd March Put It To The Vote march? A: too big to ignore

I was not able due to other commitments to pay more than passing direct attention to the People’s Vote in central London on 23rd March.

As might be expected I’m no fan of the named organisers but that is hardly the point. A very large demonstration brings all sorts of people and ideas onto the streets and opens up possibilities.

The organisers pre-claimed the march would be a million strong and repeated that afterwards as well. To be fair with such a large march over a relatively short distance ending up in a restricted space its very difficult to tell. My general views on the size of protests are here:

There were some slightly odd claims. One twitter post showed the Mall full for a Royal event in a previous…

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Do-It-Yourself Supernova Explosion

Posted in Education, The Universe and Stuff with tags , , , , on August 15, 2014 by telescoper

Visitors to the office of the Head of the School of Mathematical and Physical Sciences at the University of Sussex often remark upon the presence of these two objects and inquire as to their purpose:


Since I don’t play golf and am a bit long in the tooth to be a fan of Peppa Pig, most assume that it must be for some strange astrophysical reason. I tried asking on Twitter what people think I use them for, and the most common answer was to demonstrate the relative size of the Earth and Moon. As Roy Walker would have said, “That’s a good answer, but it’s wrong”.

In fact I use the objects concerned to demonstrate what goes on when a star goes supernova.

The point is that a supernova explosion begins with gravitational collapse of the progenitor star, so why does that manifest itself as an explosion? The point is that the outer layers are blown off while the core collapses into a compact object such as a neutron star or, perhaps, a black hole.

The way to demonstrate this is first to balance the golf ball (representing the outer layers) on top of the beach ball; the air hole in the latter is a useful place to do this. You then lift the conjoined objects to a reasonable height and drop them onto the table or bench provided for such a purpose in a lecture theatre. The objects fall together under gravity until the beach ball hits the surface. You will find that the beach ball (representing the core) stops still while the golf ball (representing the outer shells) shoots upwards as most of the kinetic energy of the system is transferred to it during the bounce.

I think this is quite an effective demonstration, but I’d encourage inexperienced lecturers to note that there is a Health and Safety Issue, so it is necessary to carry out a risk assessment before attempting it. When I first did this during a lecture many years ago, I used a ball bearing rather than a golf ball and a fully-inflated and much larger beach ball instead of the more manageable (and slightly deflated) Peppa Pig one I now use. I told the students in the audience to watch carefully what happened and then dropped them as described above…

What happened in that case was that the ball bearing rocketed up so fast that it reached the ceiling and smashed into the lights above the lecturer’s bench, whereupon there was a very loud bang and I was showered with broken glass and other debris. I have to say that got the loudest round of applause I’ve ever had while lecturing, but it wasn’t exactly the effect I’d been hoping for.

But the real reason for posting today is to wish a very happy 65th birthday to supernova expert extraordinaire and occasional reader of this blog, Robert Kirshner of Harvard University, who has celebrating along with a number of my astro-chums at a conference in Australia.

Many happy returns, Bob!