Friday, October 30, 2015


A good example of a phenomena which seems simple but which gets very complex - water flowing through a pipe.
At low speeds the flow is smooth and predictable but at higher speeds turbulence makes things complicated. According to this report:
"A team of researchers from Austria, Germany and the U.K. has succeeded in building a model that shows the process that occurs when a liquid moves from a smooth state to one of turbulence inside of a pipe."
This is a good item to use to introduce in a general way the modelling of physical processes.

Tuesday, September 29, 2015

Challenging Concepts in Physics

Need help with difficult concepts? Advanced high school or starting university level? This MOOC at EdX should help. It is done by experienced teachers and includes:
 Force Diagrams
 Rotational Motion
 Angular Momentum
 Standing Waves
 Conservation of Charge & Energy in Circuits
 Electrostatic Fields
 Gravitational and Electric Potentials
 Electromagnetic Induction
 Pressure, Force & Flow in Fluids
 Diffraction & Interference
 Atomic Transitions

The course uses short instructional videos, on-screen simulations, interactive graphs, and practice problems.
Sounds really useful.

Monday, August 24, 2015

Reflections on a mug of tea

A question for students (its good to have an open ended question sometimes):

A ceramic mug of hot tea sits on a wooden table. Discuss how it cools. (Yes I know the picture does not show a wooden table... :) )

Convection from the surface is important.
Conduction through the sides and then cooling by convection significant too.
Cooling by radiation happens too although the temperature difference is small.
Conduction through the base not important as the ceramic is a poor conductor and the wood is worse.

How can the cooling be enhanced?
Convection is easily speeded up by a higher flow of air (blowing, fan, breezy location etc).
Putting a spoon in the cup increases conduction loss.
Using a black mug will help a little.
Drastic methods! (if you are late for work) - pour into another vessel, add ice etc.

Tuesday, August 11, 2015

Thursday, July 30, 2015

New discovery in subatomic physics

This is a bit exotic but I have nothing else bookmarked for this month. The first pentaquark has been reported. This is a particle composed of five quarks - very strange but predicted. Normal particles such as protons are composed of three (see diagram) so it is like one and two-thirds of a proton - kind of.

Here is a good article explaining this starting from Rutherford's discovery of the compact nucleus of the atom over a hundred years ago.

Sunday, June 28, 2015

CXC Physics on-line resources update

Following changes the CXC website now offers syllabuses and past papers as downloadable ebooks through their 'store'. Past papers cost money to get but the syllabus has a cost of $0 which means it can be downloaded free but it is neccessary to create an account and go through the shopping cart thing.

Saturday, May 30, 2015

Inside a radiation detector

This picture shows the board of a gamma-ray detector known as a Geiger-Muller counter.  Gamma rays are detected by the tube, counted and the count shown on the LCD. The words at the top of the board warn of high voltage (400-500V).
The type of radiation detected depends on the tube used.
See Wikipedia for more.