Using Ancient Ovens to Trace the History of Earth’s Magnetic Field

Scientists have known for some time that the Earth’s magnetic field has undergone significant changes throughout the planet’s history. In fact, about once every few hundred thousand years, it completely reverses – what was once magnetic north is now magnetic south.1

There is a lot of evidence for this, the most convincing of which is the fact that if you dig down a bit, you find magnetized rocks all pointing in the same direction as each other – but that direction changes as you dig deeper, and those changes are consistent in rocks all over the planet.

Maori oven
A recreation of a Maori oven. Photo via Genuine Maori Cuisine.

Scientists are still trying to understand these phenomena, and they need more data showing exactly what the magnetic field has been up to.

Enter Dr. Gillian Turner, a physicist at Victoria University in Wellington. Edible Geography writes that Turner, along with an archaeologist, have made their own versions of old Maori ovens, like the one pictured above. They showed that these ovens could have heated rocks to high enough temperatures that they could have shifted their magnetic orientation to match the Earth’s field.

Read more at Edible Geography.

  1. The planet’s magnetic poles are a small distance away from the geographic poles, which are defined based on the Earth’s rotation.

Voyager’s Photos: Our Message to Space

Ok, I really should be getting on with the chapter on Energy, but I just had to post this.

Voyager 1, a space probe the size of a small car, will soon become the first human-made object to leave our solar system. Launched in 1977, it is still – amazingly – sending back new data about the mysteries of outer space 10 billion kilometers away, more than 35 years later.

Great Red Spot From Voyager 1
Jupiter's Great Red Spot, photographed by Voyager 1.
Voyagers 1 and 2 flew past Jupiter and Saturn, taking photos on the way. (Voyager 2 also went by Neptune and Uranus, but its path slowed it down a bit, meaning Voyager 1 is now farther from us.) Then they headed out towards interstellar space with the hope of being found, someday, by intelligent beings. Both probes were equipped with a golden record, which contained music, sounds, and images, as well as instructions on how to properly play the disks. (For more on the audio side of this project, you should definitely listen to this wonderful episode of Radiolab.)

The reason for today’s post is this gallery of images from the records, which I always find mesmerizing.

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How Galaxies Are Formed

I wanted to take a quick break from discussing the mysteries of energy to share a mesmerizing video. This NASA-created computer simulation illustrates how moving clouds of dust created in the Big Bang could accrete into the spinning collection of billions of stars that we call a galaxy.

“This cosmological simulation follows the development of a single disk galaxy over about 13.5 billion years, from shortly after the Big Bang to the present time. Colors indicate old stars (red), young stars (white and bright blue) and the distribution of gas density (pale blue); the view is 300,000 light-years across.”

Meanwhile, over at his Bayesian Biologist blog, Corey gives us an update on his attempts to find dark matter in simulated skies.

5.2 What is Energy?

Critical Questions:

  • What is energy?
  • What do all of the different types of energy have in common?

Despite its abstract and purely mathematical nature (as discussed in the previous section), we’re still going to have to come up with a good definition of energy for the purposes of this site.

The term ‘energy’ in physics means something very similar to what it means in everyday English. If you’re lying in bed and you don’t have the energy to get up, you may actually be lacking in something that could be equated with the scientific idea of energy. (Or you could just be a slothful person.) We would also say that it takes energy to light up our homes and to drive our cars, and this usage fits with the physics one as well.

Solar Flare
The best kind of energy: magic (i.e. solar flares)
Already we can see that energy has a lot of different forms – your ability to get out of bed is quite different from a car’s ability to drive down the road, for example. And yet they all have some shared quality in order for us to be able to use the same word to describe them. We do have some excellent mathematics to help us define that similarity, but for now I’d like to propose a loose definition – one which is simplified almost to the point of inaccuracy, but which will nevertheless allow us to come to a better understanding of the topic.

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5.1 Introduction to Energy and Heat

In my experience, the subject of energy tends to be badly taught in lower-level physics classes. I’ve met a lot of students who, when asked what energy is, can promptly recite the following answer: “Energy is the ability of a system to do work.” Continuing with this website’s theme of trying it yourself, I recommend that you take a field trip to the nearest university campus or high school science class and perform this very experiment, and watch the pride in the students’ eyes as they prove their intelligence to you.

sunshine, flowers, windmills, and solar power.
Fig. 12C: Windmills are just really big, genetically altered sunflowers.

But if you want to throw a bit of a wrench into things, try following up your first question with another: what is work? Many students will frown slightly. Some will say that it is a force exerted over a distance. Others will simply shrug and point at the formula. In other words, most physics students don’t really understand what energy is.

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4.3 Bernoulli’s Principle and Airplanes

Critical Questions:

  • How does an airplane stay up in the air?

You might think that today, more than a century after the Wright brothers flew that first airplane of theirs, most of the people who build and fly airplanes would agree on an explanation for how they stay up there. But just try walking into a room full of pilots and airplane engineers and asking them to explain this to you. The heated arguments and vicious character attacks that will result may well convince you never to step foot on an airplane again.

Upside Down Lynx by Captain Chaos on Flickr
Don’t even get me friggin’ STARTED on helicopters.

The reason why it’s so hard to pin down one easy explanation for the force that keeps an airplane up in the air – the ‘lift’, as it is called – is that it’s actually pretty complicated. Most simplified explanations of lift leave out some crucial details, or else they add in some incorrect ones.

The most common incorrect explanation of lift involves Bernoulli’s principle, which is interesting enough that we can spend some time getting to know about it before coming back to the problem of airplanes.

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Another Way to Learn Physics Online: Landmarks in Physics

This week, as undergrads and high schoolers everywhere are plunging into the world of Introductory Physics, I wanted to share another great resource for learning this material. It’s a course on Udacity called Landmarks in Physics. Udacity features a free, easy-to-use interface for self-guided courses taught through a combination of YouTube videos, interactive quizzes, and forums.

According to the creator and teacher of this particular course:

The class is introductory. It covers trig, kinematics, Newton’s laws, work/energy/power, simple harmonic motion, a bit of electricity, and the last unit is a very brief intro to special relativity.

The material is covered in a fairly novel way… Each unit tackles some big problem from the history of physics: for example in the first unit we learn trig as we figure out how to calculate the circumference of the earth using only shadows and some geography knowledge.

Screen grab from "Landmarks of Physics" at Udacity
All physics teachers know that drawing skills are overrated.

So if you’re looking for a slightly more mathy approach than Pop Physics has to offer, I recommend giving this one a try.