I did an experiment last night on measuring the elastic constraint forces on light rigid bodies under extreme displacements. Or, in English, I tripped in the garden and stretched various ligaments in my right foot in ways in which they aren’t supposed to be stretched. Ouch. I couldn’t put any weight on the foot at all […]
Continue readingTag: Newton’s laws
Momentum conservation again
There are some fantastic examples of momentum conservation in everyday life. This week I was attacking the leftovers from a tree removal we had a couple of weeks ago – turning the chainsaw-cut rings the tree surgeons left us into something that could be shoved into the fire come winter time (assuming no bees are […]
Continue readingJourney to the centre of the washing machine
I’m sure anyone who has ever used a top-loading washing machine will have seen this phenomenon occasionally: you lift the lid after the machine has been spinning and you find one item of clothing (such as your favourite most expensive shirt) stretched across the diameter. It happened to me last night. What’s happened is, right […]
Continue readingYou know you need a new car when…
Our cars (one of them in particular) are beginning to cause a few too many problems. Last night we were left stranded again, just outside Cambridge, and had to have those friendly AA guys rescue us. This time there was a sudden "Thwunk" sound and then a rapid "fwap-fwap-fwap" from underneath the bonnet. We pulled […]
Continue readingBending of beams
The ceiling in our new house is held up by seven large, curved, steel beams. There are also steel beams holding up parts of the upper floor. These beams are I-beams – so-called because they resemble the capital letter ‘I’ in shape (except they don’t in a sans-serif format as this blog gets published in.) […]
Continue readingOpposite charges repel, don’t they?
Well, the answer to that is, um… well…. it depends…. Now, I’m not suggesting what you’ve learned at school is not true. Take a point charge (e.g. a proton), and bring it close to another point charge (e.g. another proton) and the two will repel, with an inverse square law (Let’s not take them close […]
Continue readingThe problem with having odd-shaped balls…
…by which, of course, I mean rugby balls. To be precise, a rugby ball is a prolate ellipsoid – that is, something that is like a 3d version of an ellipse, but having a cross-section along its long axis of a circle. (A flying-saucer would be an oblate ellipsoid) Rugby balls behave awkwardly. In one […]
Continue readingMomentum conservation
It’s mid-semester break here at Waikato so I have time to breathe and get back to things other than teaching, such as seeing what the PhD students are up to. Yay. But, here’s a comment about what I was talking about last week with the first year students: conservation of momentum. If you look in […]
Continue readingFriction: Stick or Slip?
Going back to my last entry on the sliding car, it’s worth commenting a bit more on the nature of friction here. When a car goes round a corner, what prevents it from sliding is the friction between the tyres and the road. Tyres are unsurprisingly designed to be able to give a high frictional […]
Continue readingNZ Scholarship physics
I’ve recently had a look at the 2010 New Zealand Scholarship Physics exam, for the first time. (This is the exam taken by the top final year school students in physics – the best performers get rewarded with scholarships that will help them financially at university). The scholarship exams are hard. There’s no denying that. […]
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