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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 15813 letters have been answered. They are listed according to date.

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



List of most recent 15 letters

Title

Subject

Section

Country

Is pressure distributed on a bench? Physics Force USA
 
Permission to use images Physics Matter USA
 
Thanks for this opportunity Thanks Nigeria
 
Where are the attractive forces equal? Gravitation USA
 
Using 120V on equipment requiring 220V Electricity Estonia
 
A giant thank you Thanks InDesign USA
 
Connecting AC to terminals of a battery Physics Electricity India
 
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
 

Next 15 letters

 





Is pressure distributed on a bench?

Physics

August 15, 2017

Question

This article of you on pressure helped me greatly. But I still have some confusions. Such as-

If we apply force with the surface of our hand on a big bench then will the force be distributed throughout the whole area of the bench or it will just act on the portion of the bench equal to the area of our hand?

Dise - USA (28183)

Answer

The pressure on the bench will be just on the area where you push with your hand. Think of how a pillow will compress where you push your hand on it.

However, the force you apply can move the whole bench.

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Permission to use images

Physics

August 14, 2017

Question

I would like to use the phase diagram figures that you have on this page: http://www.school-for-champions.com/science/matter_states_pressure.htm

in an article that I am writing for the Health Physics Society. I understand that I need permission to use the figures. Is that possible that I could have permission to use your figures?

Thanks so much,

Linda - USA (28181)

Answer

Yes, you have permission to use the diagrams provided you cite the source.

Best wished for success in your article. Let me know when it is published.

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Thanks for this opportunity

Thanks

August 10, 2017

Question

Thanks for this opportunity

AGWOKO - Nigeria (28169)

Answer

I wish you success in your endeavors. I am sure you will be a champion.

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Where are the attractive forces equal?

Gravitation

August 5, 2017

Question

At what distance from the earth should an object lie between the earth and the sun such that the attractive force of the earth on it is equal the attractive force the sun on it , given that the distance between the earth and sun is 150million Km and the mass of the sun =3.24mass of earthh

- USA (28163)

Answer

The point where the attractive forces are equal is at the center of mass (CM) between the Earth and the Sun. See CM between two spheres for the equation.

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Using 120V on equipment requiring 220V

Electricity

July 30, 2017

Question

What happens if i use equipment thats require 220V 50Hz and i plug in it 120V 60Hz

Tanel - Estonia (28151)

Answer

If you try to use 120V on equipment that requires 220V, the equipment will probably not work at all or may work very poorly. A 50Hz device might run faster on 60Hz, but the main factor is the voltage.

Basically, it probably won't work at all.

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A giant thank you

Thanks

July 28, 2017

Question

Just a giant thank you for simplifying how to create a 3-D book cover. I taught myself graphic design so I'm very glad to have found your website.

Kira - USA (28150)

Answer

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

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Connecting AC to terminals of a battery

Physics

July 26, 2017

Question

What will happen if we connect Alternating current to the terminals of a battery?

Krishna Priya - India (28141)

Answer

You really can't charge a battery directly with AC electricity. An AC to DC adapter is needed.
It is also possible that the battery would become overheated from the AC and even explode.

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Why aren't mercury lamps used more often?

Physics

July 26, 2017

Question

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

Kanchana - India (28142)

Answer

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

Friction

July 26, 2017

Question

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)

Answer

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?

Physics

July 21, 2017

Question

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

snobbo - Zimbabwe (28139)

Answer

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

Matter

July 14, 2017

Question

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

Dronics - Zimbabwe (28132)

Answer

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

Finances

July 14, 2017

Question

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)

Answer

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

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Units of pressure and force

Physics

July 13, 2017

Question

Why pressure and force unit is same?

Pratik - India (28131)

Answer

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

Units are Pascal = Newtons per square meter

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Horizontal motion

Gravity

July 12, 2017

Question

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

Rahul - India (28128)

Answer

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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Collisions

Motion

July 2, 2017

Question




HOW DOES NEWTON'S CRADLE COUNT?

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)

Answer

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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