7 Siple Questions with No Answers七件没有答案的简单现象.ppt

7 Simple Questions with No Answers Ask a physicist about the radius of the black hole at the center of the galaxy and shell tell you more than you wanted to know. Ask her how a bicycle works, and shell shrug. It may surprise you to learn that scientists lack explanations for some of the simplest questions you might think to ask. Read on for a taste of the many seemingly mundane questions no know can answer. What causes static electricity? Static shocks are as mysterious as they are unpleasant. What we know is this: They occur when an excess of either positive or negative charge builds up on the surface of your body, discharging when you touch something and leaving you neutralized. Alternatively, they can occur when static electricity builds up on something else — a doorknob, say — which you then touch. In that case,?you?are the excess charges exit route. But why all the buildup? Its unclear. The traditional explanation says that when two objects rub together, friction?knocks the electrons off the atoms?in one of the objects, and these then move onto the second, leaving the first object with an excess of positively charged atoms and giving the second an excess of negative electrons. Both objects (your hair and a wool hat, say) will then be statically charged. But why do electrons flow from one object to the other, instead of moving in both directions? This has never been satisfactorily explained, and a study by Northwestern University researcher Bartosz Grzybowski found reason to doubt the whole story. As detailed last year in the journal Science, Grzybowski found that patches of both excess positive and excess negative charge exist on statically charged objects. He also found that entire molecules seemed to migrate between objects as they are rubbed together, not just electrons. What generates this mosaic of charges and migration of material has yet to be determined, but clearly, the explanation of static is changing. Why is yawning contagious? Last year, Austr