Is the Mpemba Effect Real?

       For more than 2,000 years, scientists have    observed    the    unique phenomenon   that,    in    some conditions, hot water freezes faster than cold water. In the fourth century B.C.E.,  Greek  scientist  Aristotle noted, "The fact that the water has previously been warmed contributes to its freezing quickly: for so it cools sooner:'
      
      Seventeenth-century   English   scientist Francis Bacon noted, "slightly tepid water freezes more easily than that which is utterly cold." Several years later, French mathematician Rene Descartes echoed his predecessors' observations, writing, "One can see by experience that water that has been kept on a fire for a long time freezes faster than other."   

    

     Given the centuries old knowledge that hot water does indeed freeze faster than cold in certain circumstances, it should have come as no surprise when Tanzanian schoolboy Erasto Mpemba claimed in his science class in 1963 that ice cream would freeze faster if it was heated first before being put into a freezer. "You were confused," said his teacher; "that cannot happen." Mpemba's assertion also amused his classmates-but their laughter quickly turned to a murmur of assent when a school supervisor ran the experiment and proved the young man correct.

      

  Scientists   have   offered   many explanations to account for the unexpected phenomenon, but to date none has been accepted  by  the  wider  scientific community. Here are a few suggestions: 

   EVAPORATION :. As the warmer water cools to the temperature of the cooler water, it may lose large amounts of water to evaporation. The reduced mass more easily aIlows for the water to cool and freeze.  

   

   DISSOLVED GASES: Hot water can hold less dissolved gas than cold water. This may somehow change the properties of the water, making it easier to develop convection currents, and therefore easier to freeze. 

   FROST: Frost conducts heat poorly. If the containers of hot water are sitting on layers of frost, the water will cause the frost to melt. This would establish better thermal contact with the cold refrigerator shelf or floor.  To date, experiments have not adequately illustrated which, if any, of the proposed processes is the most important one. "It seems  likely  that  there  is  no  one mechanism that explains the Mpemba effect for all circumstances," explained Monwhea Jeng of the Department of Physics at the University of California, in 1998.

How Were the Pyramids Built?

 

  

     

    The pyramids built by the ancient Egyptians are among the most well known and celebrated in the world. Egyptians engineered the model for what most of us consider the classic pyramid design: a square base and four smooth triangular sides.

       

  The awesome design and massive size of the pyramids have evoked some fanciful explanation .  some people have suggested that inhabitants of the  legendary Atlantis civilization,   biblical Noah, and even
extraterrestrials built them , while others claim levitation was  used or that  Egyptians possessed a now lost, unique  technology to help them erect the  remarkable structures.

    

    Indeed, there is no known Egyptian  hieroglyph or relief or any surviving  written account from that time depicting  the building of the pyramids. For centuries,  Egyptologists,    scientists,   engineers,  writers, and mathematicians have theorized  how the pyramids were built. All agree,  however, about the basic techniques of  pyramid construcrion.    Copper chisels were used to quarry soft  rocks such as sandstone and limestone, while dolerite, a hard, black igneous rock, was used on granite and diorite. The blocks were transported  from quarries usually located in Aswan to the construction sites down che Nile River on rafts or barges during the rainy season.   

       

  Without  knowledge  of  the  wheel, pyramid builders used teams of oxen or  manpower to drag the  stones-many weighing more than 60 tons (54,431 kg)    on a smoothed, level surface built from the    Nile to the construcrion site. The stones   were pulled on sleds or on rolling logs, and   the roadways may have been lubricated   wirh oil or water.      The  big debate of archaeologists,  scientists, and professionals centers upon   exactly how the massive stone blocks were   lifted ro the top of the pyramid as it was  construted upward. Extant ramps-made  of mud, brick, earth, or rubble mixed with  fragments of brick for added stability and  strength-have been found at several  pyramid sites over the years. Some  Egyptologists theorize that side ramps  could have been erected, spiraling around  the four sides of the structure, while others suggest a steep staircase-type ramp. Some propose a straight, sloping ramp built from the ground to each side, which was constantly raised as the pyramid rose. One recent theory suggests that two types of ramps were used: an external ramp to build the botom portion of the pyramid and an internal ramp to complete the structure.        

     

    Recently discovered tombs of pyramid      workers indicate that the structures were      built by paid laborers, rather than by slaves      as previously believed. Many of the     laborers were farmers and local villagers.     who considered it a high honor to work for    their god-king rulers and build their    monuments. The workers were provided    food, clothing, and decent housing, and   many received tax breaks and other perks   for their efforts. Modern Egyptologists   estimate as many as 30,000  laborers   worked on a single pyramid.    

    

    Whatever   the   exact   construction  process, it is undeniable that the ancient  Egyptians    engineered    some    of  humankind's  most  massive  and  awe- inspirlng building projects. Archaeologists are certain that they achieved their success without supernatural aid-and' certainly without the assistance of alien beings.

What makes a Boomerang Come Back?

    The boomerang is one of humanity's oldest   heavier-than-air flying inventions. King  Tutankhamen, who lived during the 14th   century, owned an exterisive collection, and aboriginal australians used boomerangs in hunting and warfare at least.as far back as 10,000 years ago. The world's Oldest boomrang, discovered in Poland's Carparthian Mountains, is estimathed to be more than 20,000 years old.
  

   Anthropologists theorize that the first boomerangs were heavy projectile objects thrown by hunters to bludgeon a target with speed and accuracy. They were most likely made out of flattened sticks or animal tusks, and they weren't intended to return to their thrower-that is, until someone unknowingly carved the weapon into just the right shape needed for it to spin. A happy accident, huh? 
 
   Proper wing design produces the lift needed for a boomerang's flight, says John "Ernie" Esser, a boomerang hobbyist who works as a postdoctoral researcher at the Universicy of California at Irvine's Math Department. "The wings of a boomerang are designed to generate lift as they spin through the air," Esser says. "This is due to the wings' airfoil shape, their angle of attack, and the possible addition of beveling on the underside of the wings."   

   But a phenomenon known as gyroscopic precession is the key to making a returning boomerang come back to its thrower. "When the boomerang spins, one wing is actually moving through the air faster than the other [relative to the air] as the boomerang is moving forward as a whole," explains Darren Tan, a PhD student in physics at Oxford University. "As the top wing is spinning forward, the lift force on that wing is greater and results in unbalanced forces that gradually turn the boomrang." The difference in lift force between the two sides of the boomerang produces a consistenc torque that makes the boomerang turn. It soars through the air and gradually loops back around in a circle.

Is Light a Wave or a particle ?

     For centuries, scientists debated the nature of light. Some claimed that light was a wave, behaving like a ripple in a pool. The opposing view was that light was a particle, like the droplets of water that flow from a kitchen faucet. Just when a prevailing view gained momentum, evidence for the other caused confusion. Finally, in the early 20rh century, Albert Einstein called a tie: Light is both wave and particle.

    Those who believed in the particle theory of light followed Sir Isaac Newton. He described light as a series of particles, using a prism to prove his theory. To Newton, the clarity and sharpness of the prism shadows meant that light traveled as a shower of particles, each following a straight line until disturbed. 

    Those who opposed Newton's theory followed  scientist Christiaan  Huygens, who   cited   light's   diffraction   and inrerference as proof that it is a wave. Diffraction, the bending of light as it passes around an object, and interference, when waves combine to form greater or lesser amplitude, occur in other mediums with wave-like properties, such as sound and water. Astronomers studying moving galaxies proved that light follows the Doppler Effect, the name for the change in sound as waves from the source move closer or fanher away from you, elongating
as they move away and shortening as they   come closer. Visible light, as seen in the   colors of the rainbow, exhibits similar  properties, with longer wavelengths  appearing as a red shift and shorter  wavelengths as a blue shift. Until the turn  of the century, this overwhelming evidence  convinced most scientists that light was a  wave, until Albert Einstein settled the  score. 

  One thorn in the argument for light-is-  a-wave purisrs is a phenomenon called the  photoelectric effect. When light shines on a  metal surface, electrons fly out. But higher  intensity of light does not cause more  electrons to be released, as you would expect with the wave theory. Albert Einstein srudied this effect and came up with a compelling theory that stated light was both wave and particle. Light flows toward a metal surface as a' wave of particles, and eletrons release from the metal as an interaction with a single photon, or particle of light, rather than the wave as a whole. The energy from that photon transfers to a single electron, knocking it free from the metal. Einstein's declaration of wave-particle duality earned him the Nobel Prize in physics in 1921. 

   Since Einstein's discovery, physicists have embraced this theory. Einstein declared: "We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do." Understanding light as a wave Ied to the deveiopment of important technology, such as lasers. The discovery of photons made possible the  electron microscope.   

  And thanks to Albert Einstein, we can  stop the centuries-old debace and declare  everyone a winner.