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Each day readers send in questions and feedback concerning the various lessons in the School for Champions website. A total of 15862 letters have been answered. They are listed according to date.

You can read them to further your understanding of the subjects.

List of next 15 letters





Why aren't mercury lamps used more often? Physics Electricity India
Moment static friction is overcome Friction Singapore
Where do charges go? Physics Static Electricity Zimbabwe
Why are neutrons produced in reaction Matter Zimbabwe
Changing PayPal account Finances USA
Units of pressure and force Physics India
Horizontal motion Gravity India
Collisions Motion USA
Receiving money from North Korea Finances USA
Need at least ten examples Static Electricity India
Wants to know about particle physics Physics USA
Viewpoint on gravitation and Big Bang theory Physics Gravitation Bangladesh
Helped me understand a difficult problem Thanks Physics USA
When is separation zero distance? Gravitation India
Is sound bent toward the ground? Sound UK

Next 15 letters


First 15 letters

Why aren't mercury lamps used more often?


July 26, 2017


Why we use mercury lamps more often?Is there any beneficial thing about it?

Kanchana - India (28142)


A mercury-vapor lamp uses an electric arc through vaporized mercury to produce light. The light can be very bright. The advantages is that they are more energy efficient than incandescent and most fluorescent lights. One disadvantage is that they give off ultraviolet radiation, which can be harmful to the skin and eyes. Special filters must be used.

Mercury lamps are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights.

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Moment static friction is overcome


July 26, 2017


Hello, I'm looking for information of the external forces produced by a moving object under friction.
Basically the force produced when a constant velocity is dropped to 0, or the moment when the static friction is overcome.

thanks and regards,

German A. - Singapore (28145)


If an object is moving, and the force on an object equals the resistance from sliding friction, the velocity will be constant.

If the object is not moving, and the force is sufficient to overcome the static friction resistance, there is a transition period where the friction suddenly becomes the lower value of sliding friction. It is as if it is breaking free.

Best wishes in your studies of friction.

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Where do charges go?


July 21, 2017


where does the charges go when an object losses its static charges.

snobbo - Zimbabwe (28139)


Objects usually lose static charges on their surfaces by coming near an object with opposite charges. For example, if an object has negative (-) charges on its surface, and an object with an excess of positive (+) charges comes close, the negative electrons will jump to join with the positive charged ions to neutralize the charge.

Remember that a stable atom has a positive nucleus and negative charged electrons in orbit around the outside.

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Why are neutrons produced in reaction


July 14, 2017


why the neutron produces the reaction
U + n => Ba + Kr + n

Dronics - Zimbabwe (28132)


When a neutron is added to Uranium-235, the nucleus becomes highly unstable, such that it splits into a Krypton-92 nucleus and a Barium-141 nucleus, plus three neutrons and gamma radiation.

U-235 consists of 143 neutrons and 92 protons. Barium has 85 neutrons and Krypton has 56 neutrons, plus there are 3 neutrons left over in the reaction.

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Changing PayPal account


July 14, 2017


Hi. If I have PayPal account for businesses can I change it to premier account.? Because me I want to be receiving money from legitimate company. Which one can I use for that? Pls help? Thank you for your help

Susan - USA (28134)


Your best bet is to check with PayPal Customer Support to find out your options.

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Units of pressure and force


July 13, 2017


Why pressure and force unit is same?

Pratik - India (28131)


Pressure is force per unit area: P = F/A.

Units are Pascal = Newtons per square meter

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Horizontal motion


July 12, 2017


Why does gravity not affect horizontal motion of a projectile >e

Rahul - India (28128)


The force of gravity pulls the object down and accelerates it toward the Earth. This does not affect the momentum in a perpendicular direction to the gravity.

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July 2, 2017



Maybe it is because when we have two balls for example the pulse travels in two directions. Since the collision produces an equal but opposite reaction, the pulse wave travels back through both balls that were used as the carriers of energy although no backwards motion is registered. Since the pulse travels through two balls the pulse length of two balls is rebounded back through the system so that when the pulse length reaches the end it will act to maintain conservation along the entire length of the pulse, whatever that length is, if it didn't it would actually be disobeying the law.

Additional comments:

I've read through many explanations on the internet concerning Newton's cradle but where I think they fail is that they try to describe why the center ball(s) absorb and release energy the way they do exhibiting barely any motion, by describing it through solely Newtonian laws of motion and the conservation of energy. What they should be doing is describing the phenomenon through the physics of resonance. Why? Because resonance is about the science of energy absorption, especially when resonant frequency is maintained through a system. What do I mean when I say resonant frequency is maintained through a system? It means the object that brings the energy into the system (the carrier), which in the case of Newton's cradle is the raised ball that will introduce the energy via the first collision) vibrates at a frequency which matches the resonant frequency of the other hanging balls. Since all the balls are made of the same materials and dimensions it means they all share or vibrate at the same resonant frequency. Yes quantum physics tells us no object is ever truly at rest but is in a constant state of fluctuation or vibration that is particular to the dimensions and materials of that object. Everything has a particular resonant frequency. And if the energy that is placed upon that carrier vibrates at the same resonant frequency as the object that will receive the energy, then that energy will tend to build on that object until the object is either destroyed or really rattled.

The opera singer hits a certain high note, and the sound from her voice (the carrier) introduces a vibration on the crystal glass that happens to match the internal frequency the glass is resonating at long enough for the energy to build until the glass shatters. When we say energy builds it means the glass is absorbing ever greater levels of energy. However, when you think about it the phrase "the energy builds" may not be a good way of describing what is happening, because the glass is made to vibrate, and if it is made to move, work is being done and therefore energy is constantly being released, and if something is constantly being released how can that energy build up? Well if the energy is not building up per se what are we witnessing? Maybe what we are really seeing is that the energy being applied is finding more efficient ways of moving across the glass and less energy is being wasted in extraneous movement so that the final work of creating vibration is ever more potent. When you have increasingly less energy being wasted producing extraneous, or chaotic motion, that would mean you have more energy to bring to the task of producing the final bit of work, which is the vibration or movement on the glass. The potency builds until the glass shatters if the note is held long enough

Of course there are other ways of thinking about it. If, for example, you increase efficiency you can say you decrease the resistance inhibiting the flow of energy across a system or object. If this is so then just the fact that you have objects in a system that match resonant frequency it has an implication on the way energy moves through a system, namely it opens up a pathway of least resistance which allows the flow or movement of energy through that system to be so efficient that it doesn't waste itself producing chaotic or extraneous motion. Which in Newton's cradle means the energy rebounding back to the first ball(s) used in the initial collision (Newton's notion of an equal and opposite reaction means the pulse wave from the initial collision travels in two directions, one being back towards the ball(s) used in the first collision) as well as the balls in the center load do not move until we get to the last ball, where almost like magic energy departs from a stationary, or non moving ball.

And this is essentially what we are seeing with Newton's cradle. All the objects/balls in that system resonate at, the same frequency The flow of energy through that system is so efficient that it moves without wasting energy on outward motion until it gets to the end. In this way energy is kind of like most of us. It will obey the laws, but if you give it an option to do the LEAST amount of obeying and work until the very end, it will naturally chose that option. Energy is like, "Dude I'll do the damn work, but if you give me a path of least resistance so I don't have to waste energy chaotically moving things around, all things considered I'd rather take that path and do the least amount of work moving things around until the end and then I'll do the push off in whatever proportion that satisfies the laws governing conservation." Like us energy would rather not do unnecessary work if you give it an option, and when a system matches resonant frequency you will give energy the path of least resistance and it will take it and produce very little motion until it reaches the end, or the last object at resonance.?

Dean - USA (28112)


Sorry for taking so long to answer you. These are tough questions, and I am working on adding a new Physics section on collisions.

When two perfectly elastic balls collide, no energy is lost to noise, heat, or vibrations. They bounce apart immediately according to the Conservation of Kinetic Energy and Momentum. You can visualize it by seeing that the center of mass between the objects moves forward without hesitation. This can also apply in a perfect Newton's Cradle.

Steel balls are elastic--but not perfectly elastic--such that they deform slightly on the collision before they bounce apart. In this case, some energy is lost to noise. Also, a pulse wave travels through the ball, providing the impetus to bounce apart.

I've tried to time the lag between the first ball hitting the second and the last ball in a Newton's Cradle moving to see how much is lost.

When some elastic objects are struck, they can vibrate at some resonant frequency and create a sound. A bell or tuning fork are examples.

I hope that gives you some insight on this topic.

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Receiving money from North Korea


July 1, 2017


Can a person send you money from North Korea will you be able to receive the money

Doris - USA (28111)


As far as I know PayPal does not have dealings with North Korea.

There are ways to send money to people in North Korea. as well as to receive money. This is usually done through brokers in China.

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Need at least ten examples

Static Electricity

June 29, 2017


I need at least ten examples. So please help me. Thanks!

Surya - India (28108)


Uses for static electricity can be classified as attracting things together (such as attracting paint to a car or ink to paper), causing things to repel (such as preventing sticking), and causing sparks to ignite things. There are also novelty uses, such as with children's toys. That is a start on listing your examples.

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Wants to know about particle physics


June 27, 2017


I am 70 years old. Since I've retired, I decided to enrich my brain studying science. In my studies the subject of physics was touched upon. I fell in love with particle physics! I took some chemistry about half a century ago. I would like to learn more about particle physics without going into the math. Can my poor old brain learn?

Don't know if you can answer. If not, I'll keep on searching!

Deborah - USA (28106)


It is great that you want to enrich your brain by studying the sciences. As they say, "It's never too late to learn."

I have several lessons on the basics of particle physics at Particles of Matter.

Also, you might find some articles of interest at Understanding Chemistry.

Best wishes on increasing your knowledge.

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Viewpoint on gravitation and Big Bang theory


June 19, 2017


Near about 14 billion years ago Allah/God the big bang and started evolution, now 7 divisible gravitation worlds.

“Gravitational worlds, they are moving or changing the orbit with their all family members depending on the nuclear of each other”. In this way- There has been incidence of full view of the universe at the very exact copy/invitation of the visible diagram solar system in the gravitation world. The universe has seven divisible, the first one of which is unit and the rest six are collective. The collective six gravitation are three invisible and the rest three are visible. The visible gravitation worlds are stars, planets and minor planets. The invisible gravitation worlds are black holes of various energy levels, the first one of which is the primordial black hole or Allah/God of the nuclear fusion of the universe. There have been collective six gravitation divisible of the big bang in future from the big black hole or Allah/God. At the first phase or level of the divisible is the black hole of the nuclear fusion of the clusters of galaxies or black hole named quasar. The second phase gravitation world of the quasars in future are of the black hole named pulsar or nuclear fusion of the cluster of galaxies. The third gravitation world of the pulsars in future is of the last black holes or nucleus of galaxy or the nuclear fusion of the constellations.

New Discovery of the Universe:

Pope: The most important news- about the God, Big Bang & Evolution at

Shahidur Rahman - Bangladesh (28099)


Thanks for the information and interesting viewpoint on gravitation.

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Helped me understand a difficult problem


June 18, 2017


Thank you very much for this webpage. It helped me understand a difficult problem on my physics homework. I really appreciate you taking the time to make such a detailed and clear page.

Cheyenne - USA (28098)


I'm glad the material was useful to you. Best wishes for success in your studies.

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When is separation zero distance?


June 17, 2017


1. Husband 70kg and wife 80kg are standing 1 mtr app art. At what they will come to zero distance by Gaby universilnal gravitational law ?

Prasad - India (28095)


The force is measured from the centers of mass of the two objects or people. Even when the husband and wife come into contact, there still is a separation between their centers, such they never will be at zero distance. See Gravitational Attraction Between Boy and Girl for more information.

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Is sound bent toward the ground?


June 15, 2017


A simple question that I assume has a simple answer. I have assumed that noise travels in all directions from the source of the noise. Does it go in a straight line assuming no distortion by wind? So if noise from a road is reflected and absorbed by a sound barrier the direct undiluted transmission noise will be reduced. Assuming the above is correct, my question is will noise passing over a noise barrier just exhaust itself and not return to land or will it be forced down to the ground and house level by any force other than wind? What type of distance will be involved and will the situation be exactly the same with or without a sound barrier added close to the source of the road noise, please? Many thanks.

ROBERT - UK (28094)


Some of the noise from a road that passes over a wall or noise barrier can be redirected toward the ground due to diffraction of the sound at the edge of the barrier. See Diffraction Affects Blocking Noise.

The amount of the diffraction or bending is a function of the frequency of the sound. I'm sorry, but I don't have the calculations for determining the distances or bending of the waves.

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