Minute Physics

This was a very brief minute physics. There is a time and place for everything. We approach the middle of the semester, and a certain tiredness has set in as a mood across campus. Few people were rushing across campus, and mostly they were stressed. So I packed it up again after 25 minutes. We will know when the right time returns. The next several weeks will be filled with observatory events: open house, high school visits, other group events, etc., all of which contain many opportunities for outreach experiments. Perhaps, this isn't the right time for minute physics outside.

On a windy warm September day, the eyes were brought to the mall. The Pasco Eye models allow to see how the optical image formation in the human eye takes place. One also can gain some understanding how the lens focuses on objects in different distances, and how glasses can correct myopia and hypermetropia. Twenty-one people stopped to see the inverted images on the retina.  The Look-into-my-eyes handout explains a few activities.

Two things are problematic on a warm September day: wind and wasps. I was unable to eat my lunch during Minute Physics due to wasps, and the wind blew over the white board, breaking one of its legs. But - that will be a problem for another day.

Around 80 F, and clear bue skies. Finally the sun was bright enough to allow seeing the spectral absorption lines that appear in the solar spectrum. They were first described by Newton in 1666, and systematically classified and catalogued by Joseph Fraunhofer in the years following 1814. This opened the door to the wide field of spectroscopy - the method of using spectral lines to analyze the  chemical composition of an absorbing or emitting medium. The Fraunhofer lines in particular refer to the dark lines in the solar spectrum, mostly caused by atomic elements in the corona of the sun. Their wavelengths provide a fingerprint of the electronic energies present in an atom, and therefore identify the chemical element.  The handout describes how to use the simple STAR spectrometers to see them, and gives some more information on their formation. We do not look at the details of spectra often enough, in particular in our everyday lives as physicists. If YOU get your hands on a prism, a diffraction grating, or even old-fashioned CD to use as a diffraction grating - try different light sources. 

Maybe it was too warm, or maybe the semester stress is beginning to take a toll. I only talked to eighteen people today.

High-altitude smoke and late-summer heat made campus a sleepy place between 1 and 2 pm on a Wednesday. Nevertheless, 25 people stopped to learn about the shadow path, or better, the solar path in the sky throughout the year. The equinoxes are the only two days of the year in which the shadow of a stick traces out an exactly straight line running from West to East. Any bored little kid might have discovered this. It was known to almost all ancient civilizations on Earth, often leaving behind architecture that displayed a special alignment around the equinoxes. The handout for this describes the relation to the local solar coordinates, azimuth and altitude. This Solar Tracker for Morris, MN, USA (45.5 degrees North), can be printed out, and you can mark shadow path of your very own when placing it into a southern window, or outside on a horizontal surface. A toothpick, cut to the correct length, and a chewing gum to stick it into the right spot, are all it takes. You even can use it as a calendar.

If you'd like one for another geographical latitude, you can ask me (sboyd@morris.umn.edu) to send you one.

I took the Kestrel handheld weather stations out, and had students measure the atmospheric pressure at their feet and at their high outstretched arms. The atmospheric pressure gradient close to the surface is about -0.1 hPa/m, or a loss of 1 millibar for each 10m of altitude gained. Most observed a pressure drop of around 0.2 hPa (or 0.2 millibar).  The handout did not miss a chance to direct people to find out how to measure the height of a building using a barometer. Twenty-five people visited.

After days of juicy heat, it finally had become pleasant again outside. "Cloud in a Bottle" entails the rapid expansion of unsaturated air in a flask to form a fog of droplets. Thirty one people stopped to make a cloud, several asked about things such as the role of condensation nuclei, or why an air parcel would expand in the atmosphere (convection!), or generally why this works. 

This may not be a good experiment for the outdoors. The flasks were heated up by scattered solar light, inhibiting the effective cooling necessary to form a cloud. Another issue is the influence of humid air on matches. So, this activity might be better held indoors 

The day before classes begin has so many friendly and open-minded people walking across campus! It was time for Major Tom in his tin can to give everone a feel for what weightlessness is. The handout for zero-g is here. I talked to thirty people, most of them students. Several walked away with a "wow-I-didn't-know-that!".  That's what Minute Physics is all about, right?

The night before had another beautiful Aurora, visible throughout the northern United States, giving the chance for the first real Minute Physics experiment. It is, of course, the week before the students return to campus. But faculty and staff are back and working to get all ducks into a row for the beginning of the semester.  The sun currently shows two gigantic sunspot groups, one of which is active region AR3780, involved in the coronal mass ejection that brought us last night's Aurora display.  A sunspotter, a few eclipse glasses, and a quickly-prepared handout on the solar cycle are enough to attract conversations about solar dynamics. Seventeen people visited - not bad for a quiet campus day. What a nice symmetry! The spring semester ended with Aurora and sunspotting, and the fall semester rings in the same way.