Science 911

So you really want to know – did dinosaurs really roam the earth in what is now Kansas? What the heck is a quark? Just call on Science 911! Our experts are the college professors who are the creators of the WEE3 Science Review and Assessment Cards. Here’s the latest installment:

I know you can compress lots of air in a tire, but can you also compress helium into a balloon? (Assuming the balloon is puncture proof) And if so, when you release the balloon will it rise five times as fast? Finally, would the balloon rise to a point of equilibrium, or continue to rise till it burst?

You could compress helium into a balloon only if the sides of the balloon were rigid like an auto tire. With real balloons the rubber stretches and expands, pushing back against the atmosphere until the elastic limit of the rubber is reached, whereupon the balloon breaks. Consequently it is not possible to “compress” helium into a conventional balloon to any real extent. If you had a very thick-walled balloon you could compress helium into it to a certain extent, I suppose. When a balloon filled with helium is set free, it rises because the density of the balloon is less than that of the surrounding air, since helium is so light. This is exactly like a piece of wood rising up from the bottom of a lake. In principle, the balloon rises until it reaches an altitude where the ever thinning atmosphere’s density is the same as that of the balloon, whereupon a point of equilibrium would be reached. In a practical sense the pressure inside of the balloon continues to expand the walls of the balloon as it rises (expanding against an ever decreasing atmospheric pressure), and at some point the balloon’s elastic limit is reached and it breaks. So, the answer to the question of whether a point of equilibrium is reached or whether the balloon breaks is determined by the strength of the balloon’s wall.

Why do Certs™ spark when you bite them in the dark? Is this electricity?

What you see when you bite into a Cert in the dark is a manifestation of what is called “triboluminescence”– the mechanical generation of light. That is to say, some substances become luminous when scratched, crushed, or rubbed. Several minerals exhibit this property, fluorite (chemically this mineral is calcium fluoride) being one. While the mechanism of light generation is not exactly clear, current thought on the matter is that when a hard crystalline material is broken into pieces (upon mechanical fracture), charge is separated momentarily in the material and light is produced upon discharge, or recombination, of the separated charges. So the answer to your question is “yes’, the light is related to electricity in the sense that it seems to arise from flowing charges. By the way, WintOGreen Lifesavers exhibit the same behavior. You might want to give them a try.

How much energy (in joules) is released when a 10 kiloton hydrogen bomb is detonated?

One ton of TNT is equivalent to 4.184 x 10^9 joules. So, a 10 kiloton hydrogen bomb would release 10 x 10^3 x 4.184 x10^9 joules, or 4.184 x 10^13 joules. (By the way, for online purposes, 10^3 means 10 raised to the 3rd power, and so on.)

I would like to know how sea level is determined? With the fluctuations of the tide what do they use as a standard? I recently read an article that stated that Mt. Everest is getting an inch taller every year as compared to sea level. How was this determined? I, and my students, would appreciate any answer that you could supply.

Thanks for this very challenging question. As I am sure you know, the measurement of Mean Sea Level is a knotty problem. There are several factors that affect the level of the sea; e.g., tidal changes caused by the Sun and Moon, waves caused by storm systems and earthquakes, and sea level changes caused by wind to name three. These introduce errors into the determination of Mean Sea Level. Until³recent years when accurate satellite altimetry became possible, mean sea level was determined primarily by making long term measurements of sea level at specific sites around the globe using tidal gauges and then averaging the observations over a wide range of stations. (The mathematical treatment of the raw data is more sophisticated than merely “averaging”, but the end result is the same.)³In the United States, the National Ocean Service has adopted a specific 19-year period as the official time segment over which tidal observations are taken and reduced to obtain mean values for tidal data. This period is called the National Tidal Datum Epoch, and the current Epoch is 1960 through 1978. The results derived from the 19-year period are reviewed annually for possible revision, with a mandatory review every 25 years. There also are several international organizations that are involved in making these measurements.³For example, The Permanent Service for Mean Sea Level (PSMSL) is one of a number of groups within the Federation of Astronomical and Geophysical Data Analysis Services (FAGS). Since 1933 PSMSL has collected and analyzed sea level data from a network of tide gauges. Their operation seems to be typical of that for other organizations that collect these types of data. As of mid-1999 the database of this Service contained over 46000 station-years of monthly and annual mean values of sea level from over 1800 tide gauge stations around the world. About 200 national authorities add data to this database. These data have³been used extensively in studies to determine long term changes in global sea level during the past two centuries. This method,³employing gauges to measure tidal sea levels, introduces other potential errors into the Mean Sea Level determination, such as³susceptibility to recording error due to reliance on human observations, possibility of marine fouling the gauge, and changes in the height of the gauge, to name a few. The United States has installed a new state-of-the-art water level measuring system that overcomes most of these potential errors. The use of satellite altimetry in this decade has presented an opportunity to establish a more accurate observational system for global sea level measurements. The ERS-1, TOPEX/Poseidon, ERS-2, GFO-1, Envisat, and EOS-ALT satellites are accurate enough to determine changes in Mean Global Sea Level of 1 mm/year. These satellites also have allowed the accurate determination of the elevation of benchmarks, against which the elevation of tidal gauges are measured and changes in land elevation are detected. The principle source of errors from satellite data have to do with the actual orbital elevation of the satellite. It seems as if three factors have lead to changes in the elevation determination of Mt. Everest. First, the land mass of which Mt. Everest is a part seems to be rising. Secondly, there appear to have been errors in accurately determining the position of the rock that underlies the snow cover. Thirdly, the accuracy with which elevation measurements can be made has increased with the use of Global Positioning System and the other altimetry satellites mentioned above. The following are several reference web addresses which you might find useful should you and your students care to delve more deeply into this problem:

I hope that the above has been helpful. As you can tell, the determination of Mean Sea Level is fraught with potential errors, and much of the activity in this area seems to be evaluating the effect of those errors.

Why does density require units but specific gravity does not? The numbers are the same.

If you are referring to either a solid or a liquid, the specific gravity of the substance is found by dividing the density of that substance (in gm/cubic centimeter) by the density of water, which is1 gm/cubic centimeter. The numbers do not change because you are dividing by 1, but the units cancel out: ( x gm/cubic centimeter)/ (1 gm/cubic centimeter) = x.

Is medical MRI related in any way to what chemists refer to as NMR? In a recent article something was said about the discovery of NMR in the 50’s that led to MRI.
MRI (Magnetic Resonance Imaging) and NMR (Nuclear Magnetic Resonance) are based on exactly the same physical principles. It is not called NMRI, or Nuclear Magnetic Resonance Imaging, presumably because of the public’s general fear of anything that has the word “nuclear” in the title. This is an unjustified fear in the present case, since in both MRI and NMR one is just looking at the magnetic properties of atomic nuclei (primarily hydrogen). One does not use radioactive nuclei in MRI, which is a safe, non-invasive technique.