# BPHgravity

Senior Members

142

1. ## Question about electrical shock.

Static discharge or better described as charge separation can be very dangerous. Tall light poles that do not have effective bonding to the earth can build up a lethal amount of charge. Electrical installers prevenmt this occurance by addding equipment bonding conductors with the circuit conductors to assist in "bleeding" off this separaion charge. Ground rods bonded to the pole can also be effective.
2. ## Question about electrical shock.

Imagine a simple circuit consisting of resistors in a series/parallel configuration. Current will flow thorugh each resistor. The amount of current depends on the connected voltage and the value of resistance of the resistor. Each person can be assumed to be a resistor that is in series with each other and possibly in parallel with the circuit. The typical resistace of a human person can range from 1,000 ohm to 100,000 ohm. In all likely-hood, the last person would receive the least amount of shock potential from the series of voltage drops that would occur across each person. If the voltage reduces to under 40-volts, it would no longer be lethal.
3. ## Capacitor

I deal with capacitors on a very frequent basis, so i am well aware of the dangers involved. My first post stated this concern very clearly. The fact that I was trying to point out is that the origin and circumstance of the cap in question is known. It is being removed from a monitor that has been de-energized. Knowing this, per the requirements of NEMA/ANSI specifications and listing by UL, the cap is required to have a discharge circuit that reduces the voltage potential of the cap to under 50 volts in under one minute. When a cap is pulled from a shelf or has an unknown orgin, OSHA recommends discharge through a 1 K ohm, 10-watt resistor for all caps up to 1,000V, 500uF. My other point is that discharge through an insulated conductor will not "melt" the wire. Caps discharge in five time constants (TC). A TC=R*C. So if R = 0 then theoretically the cap discharges instantly. So it is important there be some resistance. How much resistance depends on how long a discharge time you want verse the size of the cap. For example a 300 micro farad cap discharged with a 100 ohm resistor would discharge in 5 * .0003 * 100 = .15 seconds. An insulated copper conductor can withstand 1A for every circular mil for 5 seconds. Common #12 awg wire has 6,530 circular mils. So trust me when I say the wire will be fine.
4. ## Question about electrical shock.

Current doesn't just take the path of least resistance, it takes all paths of resistance to its source, not to the ground. If a person or in this case a series of persons come in contact with an energized component of an electrical system and are insulated from a conductive path to the source, no potential will exist, and in effect no current will flow and no shock will occur. Most systems in the US have significant system grounding to Earth and in some cases to the buiding foundation and structural supports. There is a possibility that a very high resistance path could be created through one if not all the persons in contact with ground in the case of standing on a concrete floor or the Earth itself. A scenior that would certainly cause for all persons to receive shock is by having the last person in line in contact with a object that is bonded to the electrical grounding system, like an appliance. This way a return path for current exists and current will use the persons as a conductor.
5. ## Capacitor

Your all nuts! Short the leads with a short peice of any small gauge wire or a few quick taps with a screwdriver is all you need to do. If the unit was denergized for any period over a few minutes, the internal circuitry has already dischraged most of the eneregy from the cap. All that will be left is some residual charge. 4,000 or 40,000 amperes at 1/100 of a second isn't going to melt a copper conductor anyway.
6. ## SPDT Switches

This is usually for interference suppression. Your circuit looks good. I personally would install an interlock that holds the paired switches from being operated independently and add a stop switch in series with each motor for an off fuction. This allows single function control and prevents two off postions from existing.
7. ## Capacitor

If the capacitor has a full charge on it, you could receive a pretty severe shock from contact with the two terminals. Equipment with capacitors are required by Underwriter Laboratories to have permanent and automatic means to discharge capacitors to a residual voltage of under 50-volts nominal within one minute after disconnecton from the power source. Still, it only requires 15-mA to kill a person, so don't take any chances. All you need to do to completely discharge the capacitor is to short the two leads. A simple loop of insulated wire is all that is needed.

Try using two plastic cups and some string
9. ## Are Cures The Cause?

It seems to me that when a virus or illness is eradicated from Earth, another much worse one follows. For example, measels, plague, polio, small pox; all these horrible diseases have been removed by large from human civilization, yet cancer, HIV, and others have followed. My question is; is it possible that nature and evolution has automatic population control? Meaning, AIDS has a purpose. It is meant to limit the over-population of the Earth. With the finding of a cure, what will nature retaliate with? This also extends to the possible origins of homosexuality. Is it possible that nature and evolution is forcing population control by changing our sexual tendencies and thus reducing births? Mathematically speaking, the larger the homosexual population, the lower the birth rate. Makes sense to me. Has nature and evolution figured out that if viruses and disease doesn't slow our growth, changing human sexuality will?

11. ## Earth's Magentic Field

Is it possible for the Earth's magnetic field reverse in polarity? I have recently read an article that suggested the Nothern Aurora is getting weaker due to a change in the flow of molten magnetic material in the center of the Earth. This in effect will flip the magnetic poles. It also suggested the Earth's magnetic field may have reversed several times in its history. I've never heard of this.
12. ## Screen Savers

http://setiathome.ssl.berkeley.edu/
13. ## Can Oxygen freaze?

-218.79 degrees C.
14. ## Mental Fatigue

I have recently been studying for a very important professional exam that I will be taking later this summer. I have been reading and working problems in 3 or 4 hours sessions. On occasion, I get to a point that I can't concentrate, focus, or even keep my thoughts straight. I feel as if my brain is about to explode. However, I can simply turn on the TV, go on my computer or do some other activity and the fatigue instantly goes away. What chemical and physiological cahnges take place at the moment mental fatigue sets in and how does the brain know the difference between reading for the sake of work verses reading for the sake of pleasure? With physical fatigue, simply changing physical activity doesnt make the fatigue go away. Only rest will. However with mental fatigue, simply changing the focus of mental activity does. Why?

27/m/USA Birthday on Turkey Day every few years.
16. ## Awe, Awesome, Awful

Awe: An emotion of mingled reverence, dread, and wonder inspired by something majestic or sublime. Awesome: Inspiring awe, full of awe, of greatness Awful: Extremely bad or unpleasant, terrible horrible and dreadful So basically, if you have some awe, it is fantasic and good. But if you are full of awe, it is a horrible and bad. What gives?
17. ## Where are greenhouse gases located?

Isn't water vapor technically a "greenhouse" gas? I would think greenhouse gases would concentrate at all levels of the atmosphere depending on its properties and how they react with other natural gases in those areas.

Hey, little photon, am I right? You and your brothers make up light, Get up close and form a stream, Work together as a team? Hey, little photon, do you act alone, Or only with the other clones? Be a wave of specific length Or a particle of unknown strength? Hey, little photon, What's it like out there? Out in space and unaware You could come to earth and hit my eye And make me see. Do you die? Part of universal history, Backdrop to the human mind You might be real or just a fable - Will us humans one day find In searching out your mystery That reality is just a label?

20. ## Force in coil

Coil guns are actually quite common and easy to make. Many electrical engineering schools or electrical apprenticeship facilities have played with the concept. A coil essentially takes on the properties of a bar magnet when a current is passed through it. A North and South pole can be determined by current direction. If a magnetic material is placed near the energized coil, it will be attracted to the coil, if the direction of current is switched at the appropriately calculated time, the coil will repel the material and shoot it out the other end.
21. ## Synesthesia

I have recently become aware of this condition. (Thanks Glider!) Synesthesia is a phenomenon in which one type of stimulation evokes the sensation of another. For example, one might experience the visualization of color upon hearing a certain sound. I personally experience pleasant odors upon hearing certain music. The odors are so vivid as to almost suggest taste. I first noticed this condition during high school after being hit in the head with a baseball bat, which resulted in a severe concusion. Upon recovery I would experience moderate vertigo and funny letter stacking while reading. This is also when I first experienced the odor of "lemon" when a certain song came on the radio. The doctor I was seeing stated that the brain does some weird things after head trauma, and that it would go away. The vertigo and letter stacking did, the smells didn't. I am now aware of at least three trigger songs that produce this experience, all producing different smells. Is there anyone else on this forum or do you that know of someone with this condition? Please share. Thanks.
22. ## Musical Hallucinations

WOW! Thank you very much for sharing this comment. I had never heard of this condition nor did I realize what I was experiencing was actually a real thing. I have now done some research on synesthesia and can't believe how many examples I can find that are similar. It appears that most cases are reported as visual occurances, like certain letters always being a certain color. Thanks again!
23. ## The Official JOKES SECTION :)

Actually, there are 3 types of people, those who can count, and those who can't.
24. ## Most Important Question Ever!

Toilet Paper Orientation, over the top, or from the bottom? I personally refuse to use a roll of toilet paper that rolls off from the bottom. The correct and responsible way is for the paper to roll off from the top. Please provide your opinions and theories. My assumption is that those whom prefer the bottom feed method are partially retarded and most likely right handed.
25. ## Pressure and Heat - the relation

2) Answer: I'm going to take a wild stab at this and say 42 elephants.
×