Human Body

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Bicycling and Calories

Keywords: air drag, conservation of energy, energy transfers, metabolic efficiency, rolling friction, work done

How long do you have to ride your bicycle to burn off a doughnut?

This example looks at the relationship between physical exercise and calorie consumption.

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7 years 9 weeks ago

Nerve Impulses

Keywords: nerve impulses, neurons, reaction time

How fast does a nerve signal travel?

This example takes typical eye-hand and eye-foot reaction times and calculates the average speed at which a signal travels along the nervous system. Why are eye-foot and eye-hand reaction times different?

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7 years 9 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.

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7 years 9 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.

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7 years 9 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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7 years 2 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.

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6 years 50 weeks 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.

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6 years 49 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.

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6 years 18 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 16 weeks ago

Steam Burns

Keywords: heat, heat of vaporization, phase changed, specific heat, temperature change

Why can steam at 100 degree celsius burn worse than boiling water at 100 degree celsius?

This article explains why steam at 100 degC transfers more thermal energy to your skin than an equivalent mass of boiling water at 100 degC.

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5 years 20 weeks ago
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