Biology & Medicine

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.

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6 years 38 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.

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7 years 28 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 35 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 28 weeks ago
MRI Machines and You Keywords:

Quantum Mechanics + Radio Waves = Pictures of your Brain

An explanation of how MRI machines take advantage of nuclear spins to image precise slices of a person.

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4 years 44 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 28 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.

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5 years 36 weeks ago
How big was the aerodynamic force on Felix Baumgartner at 1342 km/h? (Or on Alan Eustace at 1321 km/h?) Keywords: aerodynamics, drag, felix baumgartner, free fall

Did you watch Felix Baumgartner jump out of a balloon gondola at an altitude of 39 km? Here's a question for your physics students, or even your physics teacher! How big was the drag force on Felix Baumgartner at his maximum speed of 1342 km/h? Pretty enormous, right? Wrong.

Knowing next to nothing about how aerodynamic drag varies as one hits the sound barrier, there is very simple way to assess the aerodynamic drag on a falling object at its maximum speed. Even at 1432 km/h. In fact the maximum aerodynamic drag occurs afterwards when the falling object is slowing down in the denser lower atmosphere. To asses how big the force was on Felix Baumgartner, we create a simple mathematical model of his fall.

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5 years 3 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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7 years 17 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.

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5 years 39 weeks ago
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 28 weeks 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 28 weeks ago
Chaos, Frog Ponds, and Red Tide Keywords: Chaos, Complexity, Population Biology

Sometimes things are less complicated than they seem...

Under certain circumstances, simple equations can model complicated results. We can make a model of a frog pond that shows this type of behaviour. Sometimes this complex behaviour can lead us to identify incorrect, or not entirely correct, causes for the behaviour.

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5 years 45 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 28 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.

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7 years 28 weeks 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 28 weeks ago
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