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Page 48 of 160 (1595 Questions and Answers)

471. In high school, we said that an object on the ground has zero gravitational energy, while an object above the ground has some. But if a hole opened up in the floor, the object on the ground would fall - so it must have SOME potential energy, right? At the center of the earth, would you have no gravitational potential energy? If not, why - doesn't the sun still pull on you?
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You've brought up an interesting subject. Many quantities in physics are only well defined relative to some reference point. For example, your velocity is only defined relative to some reference frame; typically the earth's rest frame. Viewed from a different reference frame, your velocity will be different. The same holds for gravitational potential energy. When you choose to define the object's gravitational potential energy on the floor as zero, you are setting the scale with which to work. For altitudes above the floor, the object's gravitational potential energy is positive, but for altitudes below the floor, that energy is negative. As the ball falls into the hole, its gravitational energy becomes more and more negative and its kinetic energy increases. To avoid working with these annoying negative potential energies, you should choose to set the gravitational potential energy to zero at the lowest point you'll ever have to deal with; for example, the center of the earth. But the center of the earth isn't really the limit of gravitational potential energy. The object could release even more gravitational potential energy by falling into the center of the sun. It could release still more by falling into the center of a giant star. Fortunately, there is a genuine limit. If you were to lower the object slowly into a black hole, the object would release absolutely all of its gravitational potential energy. In fact, it would release energy equal to its mass times the speed of light squared (the famous E=mc2 equation of Einstein). The object would actually cease to exist, having been converted entirely into energy (the work done on you as you lower the object, presumably at the end of a very sturdy rope). This effect sets a real value of zero for the gravitational potential energy of an object: the point at which the object ceases to exist altogether. Final note: if you drop something into a black hole, it doesn't vanish the same way, because its gravitational potential energy becomes kinetic energy as it enters the black hole. The black hole retains that energy and grows slightly larger as a result. When you lower the object on a rope, you retain its energy and it doesn't remain with the black hole. The black hole doesn't change as it "consumes" the object.

472. Is there a relationship between the black hole and the point of origin of the universe?
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Yes and no. Both involve lots of mass in a very small space. A black hole is a very strange region of space-time, where time runs slowly and the gravity is extraordinarily intense. Around the black hole, everything is swept inward through the hole's surface. But (as best I understand it) the early universe didn't necessarily have strong gravity. With mass uniformly distributed in the tiny, compact universe, an object felt gravity pulling it equally in all directions. There was as much mass to the left of the object as to its right. Thus the object would have been roughly weightless. With no gravity to make things lump together into galaxies, stars, and planets, there was no reason for those celestial objects to form. Why they did form is one of the great questions of modern cosmology. As for the universe's character at the very moment of creation, I don't think that anyone has a clear picture of what was happening. The very nature of space-time was probably all messed up and the theories needed to understand it don't yet exist.

473. What information is now available about magnetic fields and free radicals in our bodies?
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Free radicals are molecular fragments with unpaired electrons. The organic molecules in our bodies are normally held together by covalent bonds, an arrangement in which a pair of electrons orbits between and around two atoms in a manner that reduces the total energy of the atoms and thus binds the two atoms together. When only one electron is orbiting an atom by itself, it is chemically aggressive and tends to attack other molecules. That electron is also magnetic and is influenced a tiny bit by surrounding magnetic fields. My guess is that the magnetic fields you normally encounter, whether they are due to the earth's magnetic field, or to nearby power lines, or even to strong magnets such as those used in magnetic resonance imaging, have very little influence over the chemistry of free radicals in your body. Free radicals are themselves a health issue, but I don't think that magnetic fields make free radicals any more or less hazardous. If I learn more about this issue, I'll add it here.

474. What is DTMF and how can I measure the pulses on a rotary phone?
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DTMF is short for "Dual Tone MultiFrequency" and refers to the pair of tones that a telephone uses to send dialing information to the telephone switching system. Each time you press one of the buttons on the telephone, it emits two tones simultaneously. A decoder at the other end recognizes these two tones and determines what button you pushed. One tone is associated with the button's row and one tone with the button's column. Since there are four rows of buttons, there are 4 possible row tones and since there are three columns of buttons, there are 3 possible column tones. A fourth column of buttons, A through D, and a fourth column tone are part of the specifications for DTMF but do not appear in normal telephones. Naturally, all 8 tones are different and the web has countless pages that discuss these tones (touch here for an example)

As for measuring the pulses on a rotary phone, you can do this if you can study the telephone's electric impedance (or resistance). As the dial switch turns, it briefly hangs up the telephone repeatedly. The number of hangups is equal to the number you are dialing (although dialing "0" causes it to hang up 10 times). You can actually dial by hanging up the telephone rhythmically and rapidly several times. If you click the hang-up button 5 times rapidly, you will dial a "5". To detect that this hanging up is happening electronically, measure the telephone's impedance—the impedance rises dramatically during each hang-up. If there is a constant current passing through the telephone, the voltage across its two wires will rise. If there is a constant voltage reaching the telephone, the current passing through it will drop. The telephone company detects this repeated change in impedance and determines what number you dialed.


475. When astronomers study sunspots they occasionally notice that there only seems to be one magnetic pole. But I thought that monopoles didn't exist that we know of. What's going on?
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While a sunspot may have only one magnetic pole associated with it, there is sure to be an equal but opposite pole somewhere else in the sun. Probably it's located deep inside the sun or somewhere else on the sun's surface. Like one end of a long bar magnet, the sunspot looks like a single pole, but it's really connected to an equal but opposite pole.

476. If you apply the brakes while making, say, a left turn on a motorcycle, the motorcycle will tend to "stand up." That is, it will tend to fight the lean you make into the turn. Why?
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When you turn left, you are accelerating toward the left and your velocity is changing toward the left. This leftward acceleration requires a leftward force and that force is supplied by friction between the ground and the motorcycle's wheels—the ground pushes the wheels toward the left. However, this leftward force on the wheels also exerts a torque (a twist) on the motorcycle about it's own natural point of rotation—its center of mass. As the ground pushes the wheels toward the left, the motorcycle tends to begin rotating. In this rotation, the wheels begin moving toward the left and the driver's head begins moving toward the right—the motorcycle "stands up"! Actually, if you lean far enough to the left as you turn, an opposing torque due to the upward force that the road exerts on the wheels will balance the first torque and your motorcycle will experience no net torque—it won't stand up at all. On a high-speed turn, you must lean quite a bit to avoid the "standing up" problem, which is why motorcycle racers practically touch the ground as they turn.

477. Does everything (all matter) emit radiation? What about if something is at absolute zero? What about if it's inside a black hole? Does a black hole emit radiation? Are Hawking particles emitted by the black hole or are they spontaneously created? If a black hole causes particles to be created, is that the same as the black hole emitting them?
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To begin with, matter always emits radiation. That's because, at any temperature above absolute zero, the electrically charge particles in matter are in thermal motion and they accelerate frequently. Any time an electrically charged particle accelerates, it emits electromagnetic radiation. If you could cool matter to absolute zero, the thermal motion would vanish and the matter wouldn't emit radiation. However, absolute zero is an unreachable destination—it can't be achieved—so everything experiences thermal motion and emits radiation.

The issue of radiation emitted by a black hole is another story. For decades, people thought of a black hole as perfectly black—it absorbed radiation perfectly but emitted none itself. However, Stephen Hawking showed that a black hole does emit radiation and that it behaves like a normal blackbody: an object that emits thermal radiation characteristic of its temperature. The temperature of a black hole is inversely proportional to its mass. For black holes of any reasonable size, this temperature is so extraordinarily low that the black hole emits very little Hawking radiation.

This radiation originates in the vicinity of the event horizon, the surface inside which the black hole's gravity finally becomes strong enough to prevent even light from escaping. At that surface, quantum fluctuations in which particles are temporarily created and destroyed can occasionally lead to the creation of a particle that escapes the black hole forever. In effect, two particles are created simultaneously, one of which falls into the black hole and is lost and the other of which escapes forever. The particle that falls into the black hole actually decreases the mass of the black hole, and the missing mass escapes with the other particle. As for whether the black hole causes this emission or is actually doing the emission, there is no difference. The only feature that the black hole has (other than electric charge and angular momentum) is its event horizon (actually a characteristic of its mass). If the event horizon is causing the particles to be created, then the black hole itself is at work creating those particles.


478. How can I differentiate between daylight and incandescent light?
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Actually daylight is a form of incandescent light. Incandescent light is the thermal radiation emitted by a hot object such as the filament of a light bulb or the surface of the sun. But the spectrum of incandescent light emitted by an object depends on its temperature. Since the filament of an incandescent light bulb has a temperature of only about 2500° C, its light is much redder than the light emitted by the 6000° C sun. That's why photographs taken indoors with incandescent lighting turn out so orange—the light just isn't white, it's orange-red. So you can differentiate between sunlight and the light from an incandescent bulb by comparing the spectrums. Look for the relative intensities of red, green, and blue lights. Sunlight will have much more blue in it than light from an incandescent bulb.

479. Can magnetic energy be used to power a vehicle?
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When you talk about "magnetic energy," you are referring to magnetic potential energy. A potential energy is energy stored in the forces between objects. In the case of magnetic potential energy, that energy is stored in the forces between magnetic poles. But there is only so much potential energy in any given collection of objects. Potential energy is released by allowing the forces between objects to push the objects around and once it is used up, there isn't any more available. That's because energy is a conserved quantity—something that can't be created or destroyed and that can only be transferred between objects or changed from one form to another. While you can store energy in a collection of magnets, that potential energy is limited by how much was put in in the first place. So to answer to your question: yes, magnetic energy can be used to power a vehicle, but not indefinitely. The only practical magnetic energy storage proposals I'm aware of are ones that suggest using huge superconducting magnets to store electric power. While such devices might be practical for an stationary power company, they would be impractical or even dangerous in a vehicle—picture cars containing incredibly strong magnets driving down the road, repelling or attracting one another as they pass.

480. How does an integrated circuit store so much information?
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An integrated circuit is formed by using photographic techniques to sculpt the surface of a silicon crystal, to add chemicals to the silicon, and to deposit layers of other materials on top of the silicon. As part of this sculpting and coating process, a typical computer chip will have tiny memory cells formed on it. These cells usually consist of a tiny pad of aluminum on which a small amount of electric charge can be stored. To store one piece of information, a "bit", on one of these pads, electronic devices called MOSFETs—built right into the silicon surface—are used to control the flow of charge onto the pad. The amount of charge on the pad determines the bit's value. The charge remains on the pad, thus storing the bit, until it's time to recall the bit. At that time, the MOSFETs allow the charge to flow off the pad and into electronic devices that determine what the stored value is.

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