Skip to main content

Posts

Showing posts from March, 2015

Gravity Probe B Notes: Projecting Vectors via the Dot Product and the Importance of High School Trig

I'm in the process of reading Schiff's Gravity Probe B inception paper[1].  Gravity Probe B was the satellite borne experiment that detected the Earth's gravitomagnetic field, but that's not what I'll be talking about today.  This post is more about a math trick/pattern.  It's a mathematical pattern that comes up pretty frequently in physics, so I figured it was worth a few notes here.  The first picture below shows the equation for the torque on a spinning object due to a spherical source of gravity, (like the Earth), with a bit of its attendant explanation by Schiff.  My notes can be seen to the left:


The cool part I'm going to focus on today is one of the smallest expressions within the rather ginormous equation 3, (also shown in picture 2):

$$\left(\vec{\omega}\cdot\vec{r}\right)\vec{r}/r^2$$

I've run into structures like this in the past and it took me awhile to realize what they did.  Likewise for some of my classmates.  The short version of the s…

Superconducting Electrons as a Frictionless Superfluid

While doing research for an article I'm writing about Janet Tate and her Gravity Probe B experiment[4], I found a few cool things regarding superconductors, frictionless bearings, and the Egg of Columbus experiment this morning.

The Egg of Columbus demonstration was first performed by Nicola Tesla in 1893 at the World's Columbian Exposition[1].  Here's a brief video from MIT showing a modern day version of the demonstration[2]:


The MIT site[2] describes the apparatus as follows:
"A toroid with three different wire windings is connected to 220 VAC 3-phase voltage. The voltage phase of each of the three windings lags 120 degrees behind the next, creating a changing induced magnetic field. The changing field causes metal objects to rotate when placed inside.
Motors using this principle are very common. In fact, power lines are often seen in sets of three because they are carrying three phases. For more information on 3-phase voltage," Alfred Leitner made use of a s…

High Schoolers rough out a version of Cavendish's Experiment

Faced with students that didn't quite believe Newton's law of gravitation, Anthony Rennekamp
 of Bishop O'Connell High School in Arlington, Virginia, he did what any physicist would do; he had his students build an experiment.  They created a version of Cavendish's experiment using two yard sticks, two one kilogram weights, and a few 50 pound dumbbells.  You can find the write-up of the experiment on the Physics Today website[1].  Mr. Rennekamp and his students also made a video of the experiment.  Given the slow velocities with which the masses move in this experiment, the class reasoned that speeding up a video was the only practical way to view the results.  They published their experimental results video on youtube, (you can watch it below).  There was some online disbelief that the experiment could work as well as it apparently did.  I thought it would be fun to just run a few back-of-the-envelope calculations here and see if their results are reasonable.

The equa…

The Pink Cloud from Outer Space (Video Coverage)

Michael Heiland serendipitously took this phenomenal time lapse video of the pink space cloud reported over Arizona last week on 2/25/2015. The cloud was formed by the Air Force Research Lab's rocket-launched ionospheric research experiment .  The video was taken from Michael's perch on Mount Lemmon northeast of Tucson.




Based on the timing of this video showing the appearance of the cloud pretty much coincident with sunrise, the two science questions remain unanswered.

Did the substance released in the experiment react chemically with the sparse oxygen in the ionosphere causing a glow in the process, as in the first Smoke Puff experiment back in 1956[2]?

Or, was sunlight responsible for ionizing the substance in the same manner as the phosphorous payload released in the Smoke Puff 2 experiment[3]?

+Michael Heiland is a bit of a phenomenon himself.  He became famous for a gorgeous time lapse video of the Phoenix valley he made as a high school senior.  More examples of his photo…