What makes a paper airplane fly when its wings are not shaped like real airplane…

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What makes a paper airplane fly when its wings are not shaped like real airplane wings? — JC, Idaho Falls, ID

Even though a paper airplane’s wings are flat, they experience all of the aerodynamic forces found in more sophisticated wings. For example, when the air flowing past the paper airplane encounters the lower surfaces of its wings, this air slows down and its pressure rises above atmospheric pressure. However, while the air flowing over a sophisticated airplane wing experiences a substantial increase in speed and consequently a drop in pressure, this effect is very small in a paper airplane’s wing. Depending on how the air flows over or around the wing’s leading edge and whether or not it breaks away from the wing’s upper surface, the air pressure above the wing will be at or slightly below atmospheric pressure. Nonetheless, the air pressure below the wing is always slightly higher than that above the wing and the wing experiences a net upward aerodynamic force—a lift force. If you examine the airflow around a well-designed paper airplane wing, all of the flow features that occur around a sophisticated wing will be present but weak. Bowing the wing outward, as is done in a sophisticated wing, simply enhances those features so that the wing can lift a larger load.

What is a vacuum? Is it filled with charges with no mass?

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What is a vacuum? Is it filled with charges with no mass? — AW, Karachi, Pakistan

In principle, a vacuum is a region of space containing no real particles (no atoms, molecules, electrons, or other subatomic particles). Because the universe is filled with particles that pass easily through lots of matter (neutrinos, for example), it’s very hard to obtain a true vacuum. But let’s suppose that you could actually obtain a region of space with no real particles in it. That region of space would still contain large numbers of virtual particles at any given moment. These virtual particles are temporary quantum fluctuations of the vacuum; brief excursions of the quantum fields associate with various subatomic particles. These excursions are permitted by the Heisenberg uncertainty principle, which allows temporary violations of the conservation of mass/energy as long as those violations are extremely brief. While the presence of these virtual particles can only be detected indirectly, they are not massless. Except for their short lifetimes, these particles have characteristics similar to those of normal particles. In fact, if enough energy is used in the process of looking for a virtual particle, that virtual particle can be converted from virtual to real so that it can be detected directly. The energy of detection serves to “pay” for the mass of the particle so that it can leave the virtual realm and become a real, permanent particle.

Einstein’s famous equation E=mc2 says that mass is directly proportio…

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Einstein’s famous equation E=mc2 says that mass is directly proportional to energy. Does this mean that an object that is suspended overhead has more mass than an object located at ground level? — ST, Denver, CO

Yes, the mass/energy of a suspended object is greater than the mass/energy of that same object at ground level. The extreme example of this result comes with lowering an object slowly toward the surface of a black hole—as the object descends, its mass/energy diminishes until it reaches zero at the surface of the black hole.

How can I make 1000 nanometer light waves visible to the human eye?

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How can I make 1000 nanometer light waves visible to the human eye? — DMB, Broken Aarow, OK

Although our eyes are insensitive to 1000 nanometer infrared light, there are two ways to detect it effectively. The easiest is to use an inexpensive black-and-white surveillance video camera. Many of these cameras are sensitive to a broader spectrum of light than are our eyes and they can see 1000 nanometer light. If you check around, you should be able to find one that sees the light you’re interested in. The other technique is to use a phosphorescent or “glow in the dark” material. When exposed to visible light, the atoms in such a material become trapped in electronic states that can emit visible light only after a very long random wait. But exposing a phosphorescent material to infrared light can shift the states of the atoms in the material to new states that can emit light immediately. Thus exposing some phosphorescent materials to infrared light causes them to emit light promptly. You can then see these materials glow particularly brightly after storing visible light energy in them and then exposing them to infrared light. However, they’ll only glow briefly before you have to “recharge” them by exposing them to more visible light.

What are the key components of a microwave oven?

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What are the key components of a microwave oven?

In addition to the digital controller that runs the microwave, it contains (1) a power relay that allows the controller to turn on and off the microwave source, (2) a power transformer that produces the high voltage electricity needed by the magnetron, (3) a power rectifier that converts the alternating current from the transformer into the direct current needed by the magnetron, (4) a capacitor that smoothes out ripples in the direct current leaving the rectifier, (5) a magnetron that uses the high voltage direct current to produce an intense beam of microwaves, (6) a wave guide that transports the microwaves from the magnetron to the cooking chamber, and (7) a cooking chamber in which the food absorbs the microwaves and becomes hotter.

Can one’s health be adversely affected by the use of certain wraps, films, or co…

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Can one’s health be adversely affected by the use of certain wraps, films, or containers, when heating food in the microwave?

When various plastics become hot, their molecules become more mobile. The most obvious such case is when a plastic actually melts. But even before it melts, a plastic can begin to lose molecules to objects that are touching it. However, the plastics used in cooking are pretty non-toxic, so that even eating pieces of those plastic won’t cause you any significant trouble. On the other hand, I would be careful with plastics that weren’t intended for cooking. Some non-food related plastics are mixed with additives called “plasticizers” that keep them softer than they would be if they were pure. These plasticizers have a tendency to migrate out of the plastics, giving such things as “vinyl” their characteristic odors. Heating a plastic containing a plasticizer can drive this plasticizer out of the plastic and into something else. I don’t think that it’s a good idea to eat plasticizers so I would suggest not cooking with plastics that weren’t intended for use with food. Still, not all plasticizers are bad—water is an excellent plasticizer for such common plastics as hair and cotton.

When TV screens or computer monitors are shown on television shows, they flicker…

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When TV screens or computer monitors are shown on television shows, they flicker or bars of light wave across them. Why does this happen? — SY, Halifax, Nova Scotia

Although you can’t tell it by looking at a television screen, the image on that screen is formed one dot at a time by beams of electrons that are scanning back and forth across its surface from inside. The image is built one line at a time, from the top of the screen to the bottom of the screen, and each line is itself built one dot at a time, from the left side of the screen to the right side of the screen. You can’t see this sequential construction process because your persistence of vision prevents you from seeing any changes in intensity that occur in less than about 1/100 of a second. In any short period of time, the screen will only have had time to produce a few horizontal lines of dots. When a camera or television camera observes a television screen, it often makes its observation in such a short period of time that only part of the screen is built. When you then look at the recorded image, you see a horizontal bar of image—the portion of the image that was built during the observation.

How does heat affect magnetism?

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How does heat affect magnetism? — MC, Capitol Heights, MD

The magnetism we associate with a permanent magnet or with steel’s response to that permanent magnet involves the careful ordering of tiny magnetic electrons within the materials. Just as heat tends to destroy all forms of order in a newspaper when you put it in the fire, so heat tends to destroy the magnetic order in a permanent magnet or in steel when you bake them. Many permanent magnets lose their magnetism when heated to oven temperatures and even steel becomes non-magnetic when heated red-hot.

Why does copper conduct electric currents better than steel and lead? Why do cop…

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Why does copper conduct electric currents better than steel and lead? Why do copper and aluminum seem to conduct about the same? – L

A metal’s conductivity is related to how far an electron can coast through the metal before suffering a collision that reduces its kinetic energy. Since an electron can collide with an impurity in the metal or a region of local disorder, the first task in obtaining a good conductor is to make a pure and uniform metal. Increased temperature also enhances these inelastic collisions, so keeping a metal cool improves its conductivity. Finally, different metals exhibit different couplings between the electrons and the metal ions from which those electrons came. Copper and aluminum have relatively weak electron-ion couplings while steel and lead have stronger couplings. The stronger the coupling, the more likely is a collision between an electron and an ion. Because of their weaker couplings, the electrons in copper and aluminum suffer far fewer collisions per centimeter than the electrons in steel and lead. That’s why copper and aluminum are better conductors of electricity than steel and lead. The coupling in copper is only slightly weaker than that in aluminum, so they have similar conductivities. However, aluminum’s tendency to form a very hard, insulating oxide coating (aluminum oxide or “alumina” is the mineral sapphire) makes it a bit tricky to use in wiring.