Animals

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Falling Cats

Keywords: drag force, terminal velocity

Why does your cat have a better chance of surviving a fall from a large cliff than you do?

This example incorporates air resistance into free fall to derive the terminal velocity reached. The terminal velocities and physiology of cats and humans are compared.

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7 years 11 hours ago

Bats and the Doppler Shift

Keywords: bats, Doppler shift compensation, echolocation

What compensation for doppler shifts do bats perform to keep their echoes within their hearing range?

This example investigates the compensation for Doppler shifts bats perform to keep their echoes within their range of maximal hearing sensitivity.

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7 years 10 hours ago

Cheetah Chase

Keywords: constant acceleration, displacement, kinematics, uniform motion, velocity

How far away can a cheetah be from a gazelle and still be guaranteed to catch it?

This example combines both constant acceleration and uniform motion to determine the maximum distance that a gazelle can be away from a cheetah for the cheetah to have a chance of catching the gazelle.

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7 years 10 hours ago

Vision and Diffraction

Keywords: angle of resolution, circular aperture, diffraction, Rayleigh's criterion, vision

Why can eagles see more clearly farther away than we can?

The pupil acts like an aperture which diffracts light. The effect of this for humans and birds of prey is explored.

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7 years 8 hours ago

Metabolism, Heat Loss, and Size

Keywords: allometric relation, heat, heat loss, mass, metabolic rate, surface area, volume

The bigger the better?

Heat loss per unit gram is compared for large arnimals versus smaller animals.

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6 years 51 weeks ago

Flying

Keywords: aircraft, birds, energy, flight, transport cost

It takes energy to fly. How much?

We examine how much energy it takes to fly from A to B, whether by bird, model glider, small plane or 747.

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6 years 45 weeks ago

Energy Cost of Transport

Keywords: energy, transport

How much energy does it take to move a person or a tonne of freight from A to B?

We compare how much energy it takes to move something from A to B using a variety of means: road, rail, water, air, and if that something is a human, walking and bicycling.

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6 years 45 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.

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6 years 6 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.

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5 years 27 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.

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5 years 19 weeks ago
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