# Human Body

Title Post date
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.

7 years 20 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.

6 years 23 weeks ago

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.

7 years 18 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?

8 years 11 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.

8 years 11 weeks ago
How much do grade 10 students know about our energy consumption? Keywords:

Do students understand how similar we are to the machines we make?

The human body and the internal combustion engine are quite similar in that they are both heat engines requiring chemical energy to run.
By placing a question related to this notion on a national science contest, we attempted to discover what Grade 10 students think.

6 years 18 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.

7 years 52 weeks ago
Food, Energy and the Environment Keywords: energy balance, Food, greenhouse gases

How do we feed nine billion people without destroying our environment?

The primary function of food is to provide our bodies with energy. Most of this energy comes ultimately from oil, with a little sunlight added, and its production is an energy-inefficient process.

6 years 22 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.

8 years 4 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.

8 years 4 days ago
Commuting by car or cycle - which is better? Keywords: bicycle, Carbon footprint, consumption, cycling, energy, Food, spreadsheets

It's not actually that clear...

We set out to find how much of a change it would make environmentally if one cycled instead of drove to work and then further expanded our findings to include the variables of diet composition and material goods ownership.

6 years 22 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.

8 years 11 weeks ago
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.