Category: other

How do electronic water softeners, where a coil of wire is wrapped around the in…

Lou Bloomfield Leave a comment

How do electronic water softeners, where a coil of wire is wrapped around the incoming water pipe, work?

I’ve never heard of such a water softener, but I can voice some skepticism about it anyway. Hard water is water that contains substantial amounts of dissolved calcium, magnesium, and iron. These elements form multiply charged ions in solution and these multiply charged ions tend to bind with soap and detergent molecules to form an insoluble scum. To soften the water, you must remove those ions. A conventional water softener does this by replacing them with sodium ions. The active part of a conventional water softener is an ion exchange resin that releases sodium ions as it binds up the calcium, magnesium, and iron ions. Eventually the resin runs out of sodium and it must be regenerated by flushing it with strong salt water. This regenerating process flushes the calcium, magnesium, and iron ions out of the resin and puts the sodium ions back into it. As for the electronic water softener, where does it put the calcium, magnesium, and iron ions and what does it replace them with? It can’t make those ions disappear and, if it were to extract them without replacing them, it would leave the water electrically charged. So I’m skeptical that any device that doesn’t chemically treat the water directly can soften the water.

I read in an article about batteries about a Reverse Coulomb Counter. What is it…

Lou Bloomfield Leave a comment

I read in an article about batteries about a Reverse Coulomb Counter. What is it?

Although I’ve never heard of such a device myself, I can guess what it means. A coulomb is a standard unit of electric charge. Since a battery is a pump for electric charge, measuring the number of coulombs that have flowed through a battery is a way to determine what fraction of that battery’s storage capacity has been used. (It’s analogous to measuring how many grams of sand have flowed through the neck of an egg timer or how many liters of water have flowed out of a water tower.) When a battery is being recharged, measuring the number of coulombs that have flowed in the reverse direction through the battery is a way to determine how much recharging has occurred. Thus, I suspect that a “reverse coulomb counter” is a device that monitors the flow of charge backward through a battery as it is being recharged. This backward flow of charge should be almost exactly proportional to the extent of recharging.

In high school, we said that an object on the ground has zero gravitational ener…

Lou Bloomfield Leave a comment

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?

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.