Derek Covill's blog for teaching and research

a collection of subject notes, guides and projects

The Chris Hoy vs AA batteries challenge

The challenge How many AA batteries would it take to have more energy than Chris Hoy in a sprint burst? Let’s say we have a AA Duracel battery which is 1.5 V rated at 2500 mA.h (this is a good AA battery!). To understand how much energy it has stored in it, we multiply 2500 mAh…

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Energy efficiency of kettles

Energy can not be produced or destroyed: it must go somewhere (1st law of thermodynamics). Often when we build a machine to do work, some of the work is useful (e.g moving the car forward), but some of it is not useful (e.g. making grumbling noises or getting hot). When we talk about efficiency, we’re…

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Calculating energy usage

Human power and energy I like to start my analysis of power and energy with human power since it is something we can relate directly to. Let’s start with some definitions. Energy is the ability to carry out work. It is measured in Joules (SI units). Power is the rate of doing work. It is…

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