Biology & Medicine

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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.

5 years 50 weeks ago

What is a millisievert?

Keywords: dose, human health, ionizing radiation

One Sievert means exposure to enough high-energy electromagnetic radiation to deposit one joule of energy in one kilogram of living tissue. A millisievert is 1/1000 of a sievert. But how dangerous is it?

The measure of ionizing radiation dose, as is applicable to human health, is the Sievert (Sv). One Sv implies a health impact equivalent to one joule of X-rays being absorbed by each kg of living tissue. Activity, the mean number of decay events per second, is measured in Becquerels (Bq). Knowledge of the activity, mean energy release per event, and exposure time, allows to estimate the dose.

6 years 6 days ago

Heat Balance in the Human Body

Keywords: calories, energy, energy use, evaporation, metabolic rate, power, sweat, thermal radiation, thinking

How much energy does our body use? How do we keep cool when it is really hot out? Can we justify eating more when studying?

Treating the human body as a thermodynamic system, with food energy going in and heat flow due to radiation, convection, evaporation and conduction, we can see how we can maintain a constant core temperature in a huge variety of environmental conditions.

6 years 32 weeks ago

Electric Shock

Keywords: current, electric shock, electrical safety, electricity, electromagnetic induction, GFCI, ground fault circuit interrupter, induced emf, magnetic field, magnetic flux, protective devices, resistance, voltage

What effect does electricity have on the human body?

This article discusses the physiological effects of electric shock as well as a protective device installed in typically dangerous areas: ground fault circuit interrupters.

6 years 32 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.

6 years 36 weeks ago


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.

6 years 36 weeks 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.

6 years 43 weeks ago

Man on a Missile

Keywords: acceleration, force, g-force, Netwon's second law

How much force can the body withstand upon impact?

In this article we calculate the average force experienced by Colonel Stapp during one of his most famous experiments on deceleration.

6 years 43 weeks 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.

6 years 43 weeks ago

Blood Pressure

Keywords: Bernoulli's equation, fluids

Why do you feel dizzy if you stand up too quickly?

This example investigates how the pressure in the major arteries will vary depending on the position of the body and some physiological consequences of such changes.

6 years 43 weeks ago
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