Today is the anniversary of the Queen’s accession to the throne and there was a 21-gun salute from Edinburgh Castle to mark the occasion. You can see part of last year’s taken by video on the castle on YouTube. I happened to be down on Princes Street today, and caught a couple of the shots on video. Physics students should be able explain why you see the smoke from the cannon before you hear the bang. If the speed of light is 300 thousand kilometres per second and the speed of sound in air is 340 metres per second, can you work out how far away I was from the cannon?
The stunt is performed by a guy who claims to have invented a zero-friction material. If he’s right, all of the jumper’s gravitational potential energy at the top of the slope is turned into the kinetic energy of his motion at the end of the ramp. Make some assumptions and try to calculate the velocity vector of the jumper at the end of the ramp – compare your findings with the gravitational potential energy available and decide if it is at least theoretically possible to perform such a cunning stunt. If so, how much higher should the start point be, above the take-off point?
Here is my own argument for a solution for the Fermi Problem renewed in the previous post. Click on the thumbnails for each page of working… compare and contrast your own submission, perhaps.
We have winners of the competition, prizes will be presented period 2 Friday in my lab, M211.
I set a little Fermi Problem for students yesterday – with the promise of a prize for the best written argument which answers these questions.
I’ll be judging the entries tonight and deciding on prizes in time for the last day of term. I might even publish the best entries here, but meanwhile, you can read an earlier version of this exercise (which was a slightly different problem) here and my solution to it is here (click to see it full size):
This safety label was included with a laser pointer I was given recently (funnily enough, at the Institute of Physics Stirling conference in June).
The label gives handy advice about the dangers of laser pointers, because lasers are concentrated beams of coherent light of one colour – in this case, it’s a red one. The pointer is used to draw the audience’s attention to a particular area of a projected display. The label also gives basic technical information about the colour and power of the beam.
Do you have any comment on the information the label is providing?
With the timetable being so tight, and all of us so busy at the moment (you wait until *after* Christmas!), thought it would be cool to have a place where we can ask questions, prompt, encourage and support each other without having to wait until we are all in the same room.
I have created Mr. Hood’s Forum for this purpose and set up a couple of places for us to get started. I hope you find it useful. Check it out!
This tutorial shows how to draw the ray diagrams for a convex lens for the three important cases: (i) an object placed further than 2x focal length from the lens, (ii) an object placed between 1x and 2x focal length from the lens and (iii) an object placed less than 1x focal length from the lens.
You will see how in each case, the image is (i) real and inverted, (ii) out of focus and (iii) virtual, upright and magnified.
Try to construct the diagrams yourself, remembering the three construction lines from the top of the object parallel to the optical axis, through the centre of the lens and through the focal point.
On Tuesday evening, I went with a number of other Physics teachers to the Royal Observatory, Edinburgh, for an evening of information and practical observing to help teachers thinking about putting on Astronomy events in their schools.
We were given a history of the telescope and links to some very useful and interesting resources, which I thought you’d like to share:
Heavens-above.com (type that carefully) provides detailed information for observing all kinds of things in the sky from the International Space Station, Iridium Flares and of course, stars, planets and galaxies
Stellarium is a free open-source planetarium for your computer (Mac, Linux or Windows) which shows a realistic sky for your location
Finally, as well as useful tips for a successful observing evening (a hat, a red light, thinking about safety were the main ones) we were given a book recommendation: The Complete Idiot’s Guide to Astronomy.
My Advanced Highers will be joining some others on a visit to the ROE in November.
Our technical people have made us a great new resource: a tube which is drilled with tiny holes. When we push gas through the tube and light it, we get a long line of little flames. Now, when sound waves are pushed into the tube through a loudspeaker, the resulting pressure waves inside the tube produce visible sound waves in the flames. This is a Rubens Tube and it’s brilliant.
