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Bicycle Power

Keywords: bicycle, chi-squared, power, spreadsheets

How can you measure the mechanical power required to pedal a bicycle by observing how it slows down when you stop pedalling?

The forces acting on a bicycle can be estimated by observing the rate at which it slows down when you stop pedalling. This technique can, in principle, be used for any transportation vehicle.

7 years 26 weeks ago

Interference and Colour, Part II - Thin Film Interference

Keywords: absorption, colour, diffraction grating, index of refraction, inherent phase difference, interference, light, path length difference, phase, phase difference, phase shift, reflection, thin-film interference, transmission, waves

What does this beetle and a soap bubble have in common?

This article explains how by having a thin-film the waves reflecting off of the boundaries between media can interfere and result in coloration.

7 years 27 weeks ago

What do I (we) do about my (our) carbon footprint?

Keywords: Carbon footprint, reduction

A very frequent question asked by students after learning about climate change is "But what can I (we) do about it?". Here are some ideas, all of which have benefits in addition to reducing greenhouse gases, and so are worth considering even if you reject the idea of anthropogenic global warming completely.

Here is a set of suggestions for science students who wish to take action to reduce their own and their family's or community's carbon footprint. Most of the ideas are about education and attitude. We also list three achievable ways of reducing your annual emissions by least a tonne of carbon dioxide.

7 years 34 weeks ago

Interference and Colour, Part I - Diffraction Gratings

Keywords: absorption, colour, diffraction grating, index of refraction, inherent phase difference, interference, light, path length difference, phase, phase difference, phase shift, reflection, thin-film interference, transmission, waves

What gives this beetle its rainbow colours?

This article describes how colouration of an object can arise due to interference of the light waves being reflected from the object.
Periodically arranged structures which act as point sources are one means of creating the condition that at certain angles only one specific wavelength will interfere constructively. The wavelengths that interfere constructively determine the colour of the object.
Examples of colouration in beetles by interference due to periodic structures is given.

7 years 35 weeks ago

Energy cost of flying

Keywords: energy, energy loss, flight, potential energy

Gliders and planes glide similarly. How similar?

The power required to keep a toy plane flying can be inferred from the way it glides. This technique also works for full-sized aircraft.

7 years 38 weeks ago

TriColour LED Flashlight

Keywords: activity, battery, breadboard, circuit, colour addition, LED, resistors, switch, tricolour LED

Make your own TriColour LED Flashlight!

This is a straightforward classroom or summer camp activity to teach students simple circuitry and the addition of colours. The students can go home with a useful and energy-efficient flashlight.

7 years 47 weeks ago

Energy and Power

Keywords: definition, energy, types, useage

What is energy? Why is it such a useful concept? How does it relate to power?

Energy is the capacity to do work (both are measured in Joules). Power is the rate at which energy is transformed from one state to another, often from a stored state into work (a Joule of energy transformed per second is a Watt of power). Subsistence living requires about 200 W per person. Western living requires about 10 kW per person. Humankind currently uses about 12.5 TW of power, most from fossil fuels. Ten billion people living a western lifestyle (the not-impossible goal of many futurists) would require 100 TW of power.

7 years 48 weeks ago

Oil Sands (a.k.a. Tar Sands)

Keywords: fluid-particle physics, Oilsands, Stokes' Law

How do you separate bitumen from sand with the least energy cost?

Separating bitumen from sand involves the clever use of simple fluid physics.

8 years 6 weeks ago

Radioactive Milk

Keywords: activity, dose, nucleosynthesis, Radioactivity

Milk contains enough radioactive potassium-40 to set a Geiger Counter humming. But it didn't come from Fukushima, or any human activity.

Milk (and own bones) contains a lot of ancient radioactive potassium-40, which was made in a supernova explosion about five billion years ago.

8 years 15 weeks ago

Why can't you just turn a nuclear reactor off?

Keywords: nuclear reactor, shutdown

When a nuclear reactor gets into trouble, what's wrong with hitting the off switch?

When a uranium nucleus fissions into two, the resulting nuclei are not stable; they continue to decay and generate heat long after the fission chain reaction has stopped.

8 years 16 weeks ago
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