Physics

Posted by Paul A. Heckert

Indiana Jones and the Crystal Skull was, like other Indiana Jones movies, fun but not realistic. Hollywood movies usually get physics completely wrong, so when I go to movies I usually just turn off the physics portion of my brain and enjoy the story.

There was one scene in this movie, however, where they got the physics right. In one of the many death and credibility defying escape/chase scenes the old professor was riding in the back holding the precious crystal skull. They went over a bump and his treasure flew vertically upward. When it fell back down it landed right in his lap. That may seem unrealistic but the physics was exactly right. It was perhaps the most realistic portion of the chase and certainly more realistic than a sixty something archeologist doing all those death defying stunts.

Why should the skull fall right back into the old professor's lap? A fundamental principle of two dimensional motion is that the vertical and horizontal motions are completely independent of each other. Vertical motions have no effect on the horizontal motion and vice versa. When you are driving in a car and throw something straight up, the change in its vertical motion has no effect whatsoever on the horizontal motion. The horizontal speed remains the same as the vehicle's speed, so relative to the car and passengers the object seems to go straight up and down. As long as the driver does not accelerate, brake, or turn it will fall back down right on top of you. (neglecting wind effects)

The skull therefore falls right back into the old professor's lap in a rare, for an Indiana Jones movie, realistically possible scene.

Posted by Paul A. Heckert

I recently read in an article that vending machines consume 3000 kilowatts per year. The article was about installing devices that turn off the electricity consumption when people aren't around. That sounds like a good idea, but the statement is technically incorrect.

Kilowatts is a unit of power consumption, so the time is already included. So any statement that specifies the amount of time for a watt or a kilowatt must be incorrect.

Energy is measured in joules. Power is the energy divided by the time and is measured in watts. A watt is a joule per second. So a machine, vending or otherwise, that has a power consumption of 3000 kilowatts uses 3000 kilojoules of energy every second. But saying it uses 3000 kilowatts every year makes no sense. It's like saying that a car drives a total distance of 60 miles per hour every year.

To me, 3000 kilowatts sounds high for a vending machine. The main power consumption would be a few light bulbs and a refrigerator to keep the drinks cold.

Perhaps it is 3000 kilowatt hours per year, which when divided by the number of hours in a year gives a power consumption of almost 350 watts, which could power a few light bulbs and a small cooling unit. Multiplying a power unit, kilowatts, by a time unit, hours, gives an energy unit, kilowatt hours. Physicists seldom measure energy in kilowatt hours, but power companies usually do. The total number of kilowatt hours used per year makes sense.

Errors such as this one in science articles make it difficult for technically minded people to figure out the real details of the story.

Posted by Paul A. Heckert

I just finished my daily run. I didn't get moving as early as I should have this morning, so it was about 90 degrees F by the time I finished. With the heat wave in the eastern US, it is difficult to run or do other outdoor exercise.

The reason hot weather exercise is so difficult boils down to basic physics, specifically the laws of thermodynamics. The first law of thermodynamics says energy is conserved. It can change form but can not just disappear. The second law of thermodynamics says that no machine or process can be 100% efficient. There is waste energy which is converted to heat.

Applying these ideas to the exercising or working human body tells us that muscular processes are less than 100% efficient. Working or exercising muscles generate waste heat. In the winter this warms us to the point that it is possible to run through snow wearing shorts. In the summer the waste heat makes it difficult to keep our bodies cool while exercising. Therefore basic physics means that runners and other outdoor exercisers have a difficult time cooling their bodies.

If like me you run or do other outdoor exercise in hot weather, familiarize yourself with the symptoms of heat stroke and take precautions to keep your body cool. You can't violate the laws of physics.

Posted by Paul A. Heckert

The recent Phoenix lander on Mars is the first successful rocket soft landing on Mars since the Viking landers in 1976. The other intervening missions either landed inside inflated airbags or failed while landing.

Shortly after the Viking landed, I went to a talk by one of the Viking experimenters. He started the talk with a slide of a laboratory housing the equipment needed to do his experiments on Earth. The equipment filled a good sized room, consumed vast amounts of power, needed ideal conditions to function, and so forth.

The assignment from NASA was to design an instrument that could make all the same measurements, run on the equivalent of a flashlight battery, fit into a tiny package, and survive both the shock of launch and rigors of interplanetary space. Every experimenter on the Viking mission and most similar space missions has had the same assignment. Space exploration requires miniature electronics to minimize launch weight.

When I went home to relax with some music after the talk, I pulled out a 12 inch vinyl disk, containing perhaps a half dozen songs, and played it on a stereo that filled most of my living room wall. Now we can listen to music on Ipods that can store more songs than most of us have ever heard, yet are so small they are constantly in danger of being lost.

Much, but of course not all, of the early motivation to miniaturize electronic devices came from the space program's need to minimize launch weight. Once NASA learned techniques to miniaturize electronics, others applied these techniques to design music players, laptop computers and other tiny electronic marvels.

When you listen to your Ipod or use your laptop, thank the space program for getting the ball rolling.

Posted by Paul A. Heckert

Mars, the blood red god of war, has dominated our evening skies for the past several months, but it has dominated our collective imaginations for much longer.

As the latest chapter in our long term quest to explore Mars, NASA just landed the Phoenix mission on Mars' polar ice cap. The focus of the Phoenix lander and indeed much of our Mars exploration program is to answer one question. Is there or has there ever been life on Mars? Phoenix is not equipped to detect life directly, rather it will study the possibility of liquid water.

Why should we care?

We live in a universe of unimaginable vastness. Are we alone in this universe, or is it teeming with life? Based simply on the vastness of the universe, most astronomers, including me, think that we could not possibly be alone. But, we have so far found not one shred of credible evidence that there is life someplace else in the universe. This question is therefore still unanswered.

It would be less lonely if Earth life has a companion out there, so we are looking. Mars is the closest moon or planet with a reasonable possibility of life. Jupiter's moon, Europa, is also a likely candidate, but it is farther away and more difficult to get to. So we start by exploring Mars.

We still don't know if life is something that forms easily or only very rarely. If we find evidence of life or past life on Mars, then life probably arises easily and is common in the universe. If we find no such evidence, then on to Europa. We are just trying to make our vast universe a little less lonely.

Posted by Paul A. Heckert

On a recent trip to Panama I worked alongside and conversed with a fellow named Enrique. I practiced my Spanish and he practiced his English, which was much better than my Spanish. Enrique is a construction laborer, who gets by on $14 a day. He was obviously intelligent but did not have the opportunity for an advanced education, and probably does not have easy access to all the modern communications and news media that we take for granted in the developed world.

Yet when Enrique learned that I teach astronomy, he asked about the Hubble Space Telescope and the things that we've learned from it. I was a bit surprised that even people in the third world, who by necessity are mostly concerned with basic survival, have heard of the Hubble Space Telescope. Perhaps there is a lesson here.

People are curious about the world and universe around us. Projects like the space telescope, which don't have immediate applications, still excite people because they help us learn about the universe. Applications of science are important, but basic science just for the excitement of knowing more about our universe is also important. It excites imaginations all over the world.

Beyond basic knowledge and curiosity, there are many justifications for the space program in general. One that the experience with Enrique points out to me is national prestige. People all over the world know about our space program and its successes. This applies to both the manned space program and to unmanned robotic spacecraft.

Successes in space excite people all over the world by providing new knowledge and in the process increase the national prestige of the country behind the successful project.

Posted by Paul A. Heckert

Is there anyone out there or are we alone in the universe? We don't yet know, but physics is an important tool in finding out. For questions about life, most people normally think of biology, biochemistry, and similar sciences. However the best ways to search for extraterrestrial life combine all areas of science.

The search for life in the solar system involves sending robotic probes to other planets, mostly Mars. After landing, the probes rely on biochemistry to search for life. However getting the probe to another planet involves quite a bit of physics, such as rocket propulsion and orbital mechanics.

Outside the solar system, searches for life have traditionally looked for radio signals from possible extraterrestrial civilizations. That uses the physics of electromagnetic radiation. Special relativity and the speed of light limit keeps us from sending probes to other stars.

The April 2008 Scientific American has a nice article about a new strategy. Author Nancy Kiang discusses work that she and coworkers are doing on strategies for detecting vegetation on extrasolar planets. We have detected water on extrasolar planets using spectroscopy. Why not try to detect lush vegetation on a planet with similar techniques. NASA satellites use this tool and the spectral signature of chlorophyll to map vegetation on Earth. Increasing sensitivity and resolution might allow us to try this on extrasolar planets.

The trick is that plant life on extrasolar planets may have different spectral signatures. The green pigments on Earth plants are most efficient for the Sun's energy spectrum. Planets orbiting stars of different temperatures will have different spectra of natural light. Therefore plants on these planets are likely to have a different color chlorophyll and different spectral signatures. Knowing the physics of blackbodies is crucial to this analysis.

Posted by Paul A. Heckert

I once read a definition of serendipity: when you want to go fishing, dig for worms, and strike oil. If this happened in real life, there are many who would bemoan the black goo and their inability to catch fish. Only a few would recognize the value of the black goo.

Sometimes scientific discovery is like this. Serendipity plays a large role, but the scientist must take advantage of the lucky break to make a discovery. Examples of serendipitous discoveries in science abound.

In 1820, Hans Christian Oersted performed an electrical demonstration for a class he was teaching, when a nearby magnetic compass started behaving strangely. Oersted could have declared the compass broken and tossed it in the trash. Instead he investigated further and discovered a long sought connection between electricity and magnetism.

In 1967 Jocelyn Bell-Burnell was a student worker on a large radio observation project. She noticed what she called "a bit of scruff" in her data. Her fellow students told her to ignore the scruff, finish her project, and graduate. She chose to ignore the well meaning advice instead of the scruff. For her efforts, she discovered pulsars, which turned out to be the neutron stars that had been predicted more than 30 years earlier but never found. After her discovery, it turned out that a few other astronomers had observed similar effects in their data, but ignored them.

Bell-Burnell found the equivalent of black goo in her data. Her reward for not going fishing and instead investigating the nature of the black goo was the scientific equivalent of finding oil - a major new discovery.

How many scientists missed out on an important discovery because they ignored the black goo or scruff in their data?

Posted by Paul A. Heckert

Few astronomical objects capture the public imagination like black holes. These exotic stellar corpses are so dense that their gravity prevents anything, even light, from escaping. It took a while for the idea to catch on. During World War I, Karl Schwarzschild's solution to Einstein's general relativity equations predicted the possibility of black holes and their event horizons, but few scientists took the idea seriously until the 1960s.

John A. Wheeler, who is usually credited with coining the name black hole, died last week at age 96. Despite providing the name and doing much to popularize the study of black holes, Wheeler did not buy the idea at first. At a scientific meeting in 1958, Wheeler disagreed with Robert Oppenheimer and said that such objects could not exist. Wheeler however eventually came to accept the possibility that such highly collapsed stars could exist and came up with the perfect name for them.

In his book, Black Holes and Warped Spacetime, Kip Thorne, a former student and colleague of Wheeler, describes how the term originated. They had been called collapsed stars by western researchers and frozen stars by Russian workers. According to Thorne, Wheeler pondered until he found the perfect name for these exotic objects. Wheeler then simply started using the name during a 1967 meeting, as if they had always been called black holes.

How much did finding this perfect name contribute to exciting the public imagination about black holes?

Posted by Paul A. Heckert

I recently read some news articles about the discovery of the smallest black hole. It is an interesting discovery, but the headlines should read the lowest mass black hole rather than the smallest black hole.

Reading the articles, I notice that no distinction is made between size and mass. The two words are used as if they are interchangeable terms. They are not. Size and mass are two distinct properties. We can measure an objects mass, which is in grams or kilograms, with a scale. We measure its size, which is in meters or similar units, with a ruler or similar device. An object with a larger mass is not always bigger in size. For example a 10 kilogram lead weight will be smaller in size than a feather pillow having a mass of 1 kilogram.

The astronomers who discover a black hole measure its mass from its gravitational effects. They then use the mass to infer its size, which we can not measure directly. It turns out that the size of a black hole is directly proportional to its mass. Hence, a more massive black hole will be larger in size, as long as we are referring to the size of the event horizon or Schwarzschild radius rather than the central singularity point.

Not all stars however have this property. For white dwarf stars or neutron stars the size decreases as the mass increases. Using the words size and mass as synonyms for these stars will result in many incorrect statements.

Language in physics is must be very precise. Words have very specific meanings that should not be interchanged. Science writers and journalists need to use the terms correctly to avoid confusing their readers.