Probability madness

Probability crops up in many places in physics, not least quantum mechanics and statistical mechanics, where we are only sure of things in an average or 'statistical' sense. Dealing with probabilities can be a headache for many students. They are also a headache for many in everyday life. There are numerous occasions where we need […]

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The universal joint

…No, it isn’t something everyone smokes… But it is common in machine mechanisms. The universal joint is a neat way of turning rotation in one plane into rotation in another. A common use is on driveshafts where you want the direction of the shaft to bend. There’s a neat animation on Wikipedia of how the […]

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Calculating pi with darts

I love this one. Really, it's maths not physics, but there is a bit of experimental physics creeping in at the fringes when the experimenters realize that the first method is biased. The second method is much better designed.  Regrettably, pi-day (March 14th, 2015, or 3.14.15) only works if you use the US system of […]

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Check those approximations

A common technique in physics is 'modelling'. This is about constructing a description of a physical phenomenon in terms of physical principles. Often these can be encapsulated with mathematical equations. For example, it's common to model the suspension system of a car as two masses connected by springs to a much larger mass. Here, the […]

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Password entropy

As part of some 'NetSafe' training, I was shown this lovely xkcd cartoon http://xkcd.com/936/ .   Password entropy. That's a good way of putting it. The statistical mechanics definition of entropy would be k ln W, where k is Boltzmann's constant, W is the number of permutations possible, and ln is 'the natural logarithm'. Higher […]

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