The acceleration of gravity in Earth's interior is determined by the density distribution in Earth. A remarkable result is that the acceleration is approximately constant all over the mantle, which amounts to about 84% of Earth's volume. This result can be explained by a simple two-layer model of Earth, showing that the constancy of the…

During the early decades of the 18th century, Newtonian physics was still new. Much effort was expended in testing its validity. One arena in which evidence could be found was the shape of Earth. Was it perfectly spherical? On the observational side there were two hints. In 1671 Jean Richer had measured the rate of ticking of a pendulum clock near…

Simple energy balance models of planetary systems are of fundamental importance to understanding equilibrium temperatures. Most textbooks that discuss energy balance take a further step and include the effects of an atmosphere on the surface temperature. It is noticeable, however, that in such discussions of planetary surface energy balance some…

Several properties of Earth's magnetic field (field vectors, time dependence) are measured in various locations using a smartphone/tablet magnetic sensor. To enable a proper use of the magnetic sensor as a classroom tool, the exact location of the sensor in the device and its resolution must be identified in a first step. Then, students may…

Owing to the presence of the Coriolis effect, the rotation of Earth has a multitude of surprising consequences that make the mechanics of the atmosphere or the oceans different from that of a fluid in a container. Since the Coriolis effect also captures the imagination of screenwriters, contributing to the continual exposure of students to bogus…

The oscillating atmospheric CO[subscript 2] concentrations at Mauna Loa, on the island of Hawaii, Hawaii, United States of America, are Fourier transformed in order to extract the period of oscillations. Also well-known as the Keeling curve, CO[subscript 2] concentrations (in time series) at Mauna Loa oscillate in direct association with seasonal…

From the time of Pythagoras of Samos (sixth century BC), the Greek philosopher-scientists taught that the Earth was a sphere and the harmonies of the universe were governed by mathematical relations. With the fall of the Roman Empire in the fifth century, cultural darkness descended on Europe and all intellectual pursuits languished under the rule…

In this work we describe a teaching proposal to calculate the eccentricity of the Moon's trajectory by applying a geometrical technique. The values of the ratios between the Earth-Moon distance and the diameter of the Moon at apogee and at perigee were calculated from a kinematic model associated with a geometrical technique of image analysis. The…

For many students, the first--and sometimes only--chance to look through a microscope is in high school biology class, where they observe plant and animal cells up close. Even in college, few students use a microscope for a subject other than biology. Thus, it can be a surprise to learn that microscopes are a primary tool used to understand the…

With the widespread adoption of the "Next Generation Science Standards" (NGSS Lead States 2013), science teachers now aspire to integrate engineering into science instruction, as the standards suggest, yet many do not know how. The first steps are to define engineering and identify tasks that incorporate engineering, which can be…

Most students know that planetary orbits, including Earth's, are elliptical; that is Kepler's first law, and it is found in many science textbooks. But quite a few are mistaken about the details, thinking that the orbit is very eccentric, or that this effect is somehow responsible for the seasons. In fact, the Earth's orbital eccentricity is…

In the school year 2012-2013 about 50 students (Fig. 1), managed by mentors (teachers from the middle school Gimnazija Vic in Ljubljana, Slovenia) created an atmospheric probe and launched it into an altitude of more than 30 km above Earth's surface. The aim of this "space expedition" was to take pictures of Earth and to measure how air…

This column provides background science information for elementary teachers. This month's issue discusses electromagnetic waves.

This is a companion to our previous paper in which we give a published example, based primarily on Perry's work, of a graph of ln "y" versus "t" when "y" is an exponential function of "t". This work led us to the idea that Lord Kelvin's (William Thomson's) estimate of the Earth's age was…

While on a vacation flight from Hawaii to California, I observed sunset occurring on clouds far below. The view triggered a vague memory about a fun article 1 published more than three decades earlier on the topic of "Doubling Your Sunsets." Simple observations from my flight made it possible to compute the Earth's radius.