Author: Lou Bloomfield

How does a toilet work?

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How does a toilet work? — JJ, Stafford VA

A toilet is actually a very clever device that makes use of a siphon to extract the water from its bowl. A siphon is an inverted U-shaped pipe that can transfers water from a higher reservoir to a lower reservoir by lifting that water upward from the higher reservoir and then lowering it into the lower reservoir. In fact, the water is simply seeking its level, just as it would if you connected the two reservoirs with a pipe at their bottoms. In that case, the water in the higher reservoir would flow out of it and into the lower reservoir, propelled by the higher water pressure at the bottom of the higher reservoir. In the case of a siphon, it’s still the higher water pressure in the higher reservoir that causes the water to flow toward the lower reservoir, but in the siphon the water must temporarily flow above the water levels in either reservoir on its way to the lower reservoir. The water is able to rise upward a short distance with the help of air pressure, which provides the temporary push needed to lift the water up and over to the lower reservoir. At the top of the siphon, there is a partial vacuum—a region of space with a pressure that’s less than atmospheric pressure. The same kind of partial vacuum exists in a drinking straw when you suck on it and is what allows atmospheric pressure to push the beverage up toward your mouth.

In the toilet, the bowl is the higher reservoir and the sewer is the lower reservoir. The pipe that connects the bowl to the sewer rises once it leaves your view and then descends toward the sewer. Normally, that rising portion of the pipe isn’t filled water—water only fills enough of the pipe to prevent sewer gases from flowing out into the room. As a result of this incomplete filling, the siphon doesn’t transfer any water. But when you flush the toilet, a deluge of water from a storage tank rapidly fills the bowl and floods the siphon tube. The siphon then begins to function. It transfers water from the higher reservoir (the toilet bowl) to the lower reservoir (the sewer) and it doesn’t stop until the bowl is basically empty. At that point, the siphon stops working because air enters the U-shaped tube with a familiar sound and water again accumulates in the bowl. When the storage tank has refilled with water, the toilet is ready for action again.

How does wing shape affect flight?

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How does wing shape affect flight?

During flight, an airplane wing obtains an upward lift force by making the air flowing over its top surface travel faster than air flowing under its bottom surface. When the air over its top speeds up, that air’s pressure drops. Since the pressure of the slower moving air under the wing is larger than the pressure of the faster moving air over the wing, there is a net upward force on the wing due to this pressure imbalance and the wing is lifted upward. A wing also experiences drag forces—or air resistance—that tend to slow the plane down. But as long as an airplane wing doesn’t cause the airstreams flowing around it to separate from its surface, it will experience relatively little pressure drag force; the most important drag force for a large, fast-moving object.

The details of the airplane wing’s surfaces have relatively subtle affects on the wing’s performance. While most wings are asymmetric, with broadly curved top surfaces and relatively flat bottom surfaces, that isn’t essential. It’s quite possible to use wings that are symmetric, with the same curvature on their tops as on their bottoms. But a symmetric wing won’t obtain an upward lift force unless it’s tilted upward, while an asymmetric wing can obtain lift even when it’s horizontal. A broader, more highly curved wing can also obtain more lift at a lower speed, as required for slow moving propeller planes. So wing shapes are often dictated by the desired flight angle and speed of a particular airplane and its wings.

How is infrared light produced?

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How is infrared light produced?

There are many ways of producing infrared light. First, any warm surface emits infrared light. For example, a heat lamp or an electric space heater emits enormous amounts of it. That’s because the thermal radiation of a warm object lies mostly in the invisible infrared portion of the electromagnetic spectrum.

Second, many light-emitting electronic devices emit infrared light. For example, the light emitting diodes in a television remote control unit emit infrared light. In this case, the infrared light is emitted by electrons that are shifting from one group of quantum levels in a semiconductor to another group—from conduction levels to valence levels. This emission isn’t thermal radiation; it doesn’t involve heat.

Lastly, some infrared light is produced by lasers. In this case, excited atoms or atomic-like systems amplify passing infrared light to produce enormous numbers of identical light particles—identical photons. Infrared industrial lasers are commonly used to machine everything from greeting cards to steel plates.

Why can you put a can of frozen concentrate juice in the microwave? The metal do…

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Why can you put a can of frozen concentrate juice in the microwave? The metal doesn’t spark or burn.

The microwaves in a microwave oven consist of electric and magnetic fields. Since electric fields push on electric charges, microwaves cause electric currents to flow through any metal objects they encounter. These movements of current don’t necessarily cause any problems in a microwave oven. In fact, metal objects only cause trouble in the microwave oven when they are so thin or narrow that they can’t tolerate the electric currents that flow through them or when they have such sharp ends that electric charges leap off them as sparks. A thin object like a twist-tie can’t tolerate the currents and becomes very hot. Its sharp ends also allow charges to leap out into the air as sparks. But the thick, rounded end of a juice concentrate can easily tolerates the currents sent through it by the microwaves and doesn’t have the sharp ends needed to send charges into the air as sparks. It doesn’t present any problem for the microwave oven.

If you stand near a microwave oven, looking at your food, is it dangerous

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If you stand near a microwave oven, looking at your food, is it dangerous—tissue damage or make you blind?

Properly built and undamaged microwave ovens leak so few microwaves that they aren’t dangerous at all. Even if they did leak enough to be in violation of the safety limits, those safety limits are very conservative. While there is no reason to court disaster by holding your face right up to the microwave for hours and hours, it shouldn’t hurt you at all.

How do sound waves travel in space?

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How do sound waves travel in space? — PS

When sound travels in air, it takes the form of compressions and rarefactions of that air. Similar compressions and rarefactions occur when sound travels in a liquid or in a solid. But sound can’t travel through space because space is entirely empty. Sound requires a medium in which to travel and space doesn’t contain any such medium. Astronauts talk to each other by radio during space walks. With nothing at all between them, they simply can’t hear one another directly.

What is convection?

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What is convection? — DB, Corona, CA

Convection is the transfer of heat by a circulating fluid, such as air or water. This heat is carried from a hotter object to a colder object. The fluid first passes near the hotter object and receives heat. The fluid becomes warmer and more buoyant, and it’s lifted upward by the colder fluid around it—just as a hot air balloon is lifted upward by the colder air around it. The rising fluid carries the heat with it. Eventually the rising fluid spreads outward and it pass near colder objects, giving up its heat. The fluid becomes cooler and less buoyant, and soon it begins to descend back toward the ground. Eventually it’s drawn back past the hotter object and this cycle begins again.

What is a vortex?

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What is a vortex? — M

A vortex is a region of fluid that’s circulating in one direction around a line passing through that region. If you imagine yourself looking along that line, you would see the fluid flowing either clockwise or counter-clockwise around the line itself. Tornadoes and whirlpools are both vortices since they involve fluids circulating in one direction around a central line.

What are some unusual conductors of electricity?

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What are some unusual conductors of electricity?

How about graphite and cadmium sulfide? Graphite, such as that in the lead of a pencil, conducts electricity even though it’s not formally a metal. If you draw a dark line on a sheet of paper, that line can act as a wire for sensitive electric circuits. Cadmium sulfide is a photoconductor—a material that is electrically insulating in the dark but that conducts electricity when exposed to light. Photoconductors of this sort are used in some light sensors, as well as in xerographic copiers and laser printers.

Is it possible to charge batteries using static electricity? Can lightning or at…

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Is it possible to charge batteries using static electricity? Can lightning or atmospheric charges be stored in a capacitor and then released into a cell for charging? — JM, Lafayette, NT

Yes, static electricity has energy associated with it and that energy can be used to charge batteries, at least in principle. Static electricity is literally stationary separated electric charges—essentially separated charges stored on capacitor-like surfaces. As you suggest, it may be easiest to transfer these separated charges into a real capacitor and then to use this charged capacitor to recharge an electrochemical cell. Whether such a procedure can be carried out efficiently and in a cost-effective manner isn’t clear to me. The charges involved in lightning have so much energy per charge—so much voltage—that they’re hard to use for anything. Even the charges that you accumulate when you rub your feet on a wool carpet on a cold, dry winter day acquire an enormous amount of energy per charge. To charge most batteries, you need lots of low energy charges, not the small numbers of high-energy charges that are typical of static electricity. Using this tiny current of high-energy charges to charge a battery is equivalent to trying to fill a swimming pool with water from a high-pressure car-washing nozzle—too little water under too much pressure. You can do it, but there are better ways.