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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 15571 letters have been answered.



List of most recent 15 letters

Title

Subject

Section

Country

Finding coefficient of friction for a ladder Friction USA
 
Describe demographic features of the audience Speaking Zimbabwe
 
Want to know about thermal physics Physics Zimbabwe
 
Poles when breaking a magnet Magnetism India
 
I see ghosts and hear things Senses USA
 
What is the physics behind force and a lever? Machines USA
 
How do I get North American distribution rights? Publishing USA
 
Polarity of nail attracted to magnet Magnetism Philippines
 
Find the mass of the car Matter USA
 
Having an incantation of repayment Character USA
 
Can eels produce DC current in water? Electricity USA
 
Gravitational pull on girl Gravitation Italy
 
Are senses reliable? Senses Philippines
 
Advantages of centripetal force. Forces India
 
Had dream about child and other person Senses USA
 

Next 15 letters


Finding coefficient of friction for a ladder

Friction

September 22, 2016

Question

good Morning

can one use a tribology to measure the co efficient of friction for extension ladders?

is there a standard for coefficient of friction of any kind of ladder?

darlene - USA (27319)

Answer

Tribology is mainly concerned with friction and wear in machines. I don't think it would be helpful for your problem.

There are two areas where the amount of friction is an issue in a ladder.

One important area is where the ladder stands on the ground. Typically, there are rubber boots on the ladder's feet that prevent slippage. A good article on that is Tips and Techniques for Safe Extension Ladder Setup and Use.

There are various lists of coefficient of friction (COF) for combinations of materials. They are not exact but can give a rough idea. Between rubber and asphalt, the COF is about 0.7.

Another area of concern is to make sure the person's shoes are appropriate and will not slip on the ladder rungs.

Other than lists, you can determine the COF experimentally.

I hope that helps.

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Describe demographic features of the audience

Speaking

September 20, 2016

Question

describe demographic features about the audience that are to be considered when preparing an oral presentation

venancia - Zimbabwe (27304)

Answer

You need to know something about your audience before speaking to them. In what are do they live? Where do many of them work? What type of jobs or education do they have?

But also, you need to be sure they would be interested in your subject matter/

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Want to know about thermal physics

Physics

September 18, 2016

Question

I want to know more about thermal physics

tinotenda - Zimbabwe (27297)

Answer

See the lessons on Thermal Energy for information on the subject.

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Poles when breaking a magnet

Magnetism

September 18, 2016

Question

Why magnet breaks into agian a magnet having two poles again..?

karan - India (27298)

Answer

A bar magnet cannot only have one pole. When it is broken in half, the new end changes to the opposite pole. See Magnets for a picture.

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I see ghosts and hear things

Senses

September 18, 2016

Question

I see ghosts and hear things and people calling my name is I have my father died when I was seven on Christmas eve my son Dyllis 32 and the husband died years ago I am remarried and I hear ghost in my house I always Trent and things came true I always hear things

Mary - USA (27299)

Answer

This could be your 6th sense working, but also traumatic events such as deaths of loved-ones can cause such intense thoughts about them that you actually hear and see images.

Sometimes purposely trying to think about such matters can actually stifle seeing and hearing things from your subconscious.

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What is the physics behind force and a lever?

Machines

September 17, 2016

Question

Can you explain the physics behind the lever ? I know how to calculate, and understand it is the product of force*length, but I don't understand the force distribution(?) of why the force is increased due to the length ?
What is the mechanism that makes it works ?

Thank you,
Roy A

Roy - USA (27294)

Answer

That is a very good question, and it is not often mentioned in textbooks.

The relationship between forces and lengths of the lever arms is dependent on the Law of Conservation of Work and Energy. Work is defined as the force times the distance moved.

I updated several pages to show the derivation of the equation. See Increasing Force with a Lever.

I hope that helps your understanding.

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How do I get North American distribution rights?

Publishing

September 16, 2016

Question

how do I get North American distribution rights?

Nancy - USA (27291)

Answer

Typically, an author who has a book published by a publishing house will sign an agreement concerning reprint and distribution rights. At the very least, you get North American distribution rights.

Using the Amazon Advantage Program means you can sell copies of your book from the publisher on consignment through Amazon. However, it is often not cost effective.

If you self-publish your book through Amazon's CreateSpace, they list your book and take care of distribution. IngramSpark is another good source for printing and distributing self-published books.

I hope this information helps.

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Polarity of nail attracted to magnet

Magnetism

September 16, 2016

Question

If the north pole of a bar magnet suspends a nail by attraction, what is then the nails's polarity of induced magnetism in the indicated regions? Why is that so?

Jes - Philippines (27292)

Answer

The polarity of the part of the nail that is attracted to the north pole of the magnet becomes a south pole. The various domains in the iron align according to the attraction from the magnet. See Factors Determining Magnetic Properties Domains paragraph.

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Find the mass of the car

Matter

September 15, 2016

Question

The air in each of four tyres of a motor car exerts a pressure of 3.0+10n/m.each tyre is in contact with the ground over an aof 80cm.estimate the mass of the car

gladness - USA (27287)

Answer

I don't know what you mean by P = 3.0+10n/m. Also, the area must be in square meters.

Pressure equals weight / area. Weight = mass * 9.8 m/s^2
Thus the mass of the car = pressure * area / 9.8.

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Having an incantation of repayment

Character

September 14, 2016

Question

What does having an incantation of repayment have to do with being trustworthy?

Bella - USA (27285)

Answer

I'm sorry, but I don't know what you mean by "an incantation of repayment." There are several possible meanings to the phrase.

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Can eels produce DC current in water?

Electricity

September 14, 2016

Question

How do i pass an electrical DC current through water salty or not?
The electric eel can pass a high voltage through the water that hasn’t got much chloride in it then why it so hard to do? Put it this way, the eel doesn’t it very well and no one so far has given a correct answer to this question. If someone can solve this mystery that would be great and he/she would be the first to do so as I have looked everywhere and no one so far has done so.

ferdinal - USA (27286)

Answer

You can use a battery with a small light bulb and place wires from the two terminals into the water to see if the current will pass through the water and allow the bulb to light. The current will not flow through pure water, but it will flow through water with only a few impurities such as salt. This is because of the ionization of the salt molecules.

Eels product a high enough voltage that the water does not have to be very impure for the current to travel through the water and shock other animals.

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Gravitational pull on girl

Gravitation

September 3, 2016

Question

Shouldn't the gravitational pull of the Earth on the girl be 490N?

Maurizio - Italy (27262)

Answer

Thanks for the question. The weight of a person on the Earth equals the gravitational pull between the person and the Earth.

If the girl weighed 50 kg (or more correctly 50 kilogram-force or newtons), then 50 N would be the force on the girl. However, if she had a mass of 50 kg, then her weight would be 490 N.

I clarified her weight in Gravitational Force Between Two Objects. This is further explained in Confusion about Mass and Weight Units.

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Are senses reliable?

Senses

September 2, 2016

Question

WHAT MAKES A CERTAIN THAT THE FIVE SENSES ARE RELIABLE IN TELLING ABOUT OURSELF AND OUR SOROUNDINGS

AECIE - Philippines (27261)

Answer

In most people, the senses are reliable. Occasionally you may misinterpret what you see, hear, smell or such, such that you think it is something else.

However, some people have problems, such that their senses are distorted or the signals are not correctly transmitted to their brains. People with mental ailments may imagine things that are not there.

But for the normal person, the senses about themselves and their surrounding are pretty reliable.

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Advantages of centripetal force.

Forces

September 1, 2016

Question

what are the advantages and disadvantages of centripetal force.

Melvia Fernandes - India (27257)

Answer

The advantages and disadvantages of centripetal force depend on what you are trying to do. If you are swinging an object around on a rope, centripetal force is used to keep the object from flying away.

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Had dream about child and other person

Senses

September 1, 2016

Question

The story is long but I will keep it short. moved back toward family with my only child. I had injured myself, was married to a man who I was not in love with (because of things he did that were more haneious then stepmother). I ended up there they had a child needed help.

Left what I was doing (following my dreams) to go help. I was to be the godmother and this child and I was close until I asked her mother to help for three days. The phone hung up. she said it was her mother. did not speak to either of them after called to say hi to little one and she wouldn't g err t on phone.

The grandmother stated her mother was talking about you and Melissa won't go against her. When I had to move back I didn't bother, uninvited she came to my apartment. Kept her shoes on and none stop for two hour. talked about her and how she changed. Never once asked about my son or why we came back. Well curiosity got the best of me and spent some time lies cold manipulator, covering her web.

I one night sound asleep-_- I was as awoken ; ,she said I'm not your goddaughter-_- three times, I opened my eyes a young man was with brown hair-_- white robe bet toward me and beautiful. I just woke up and didn't believe someone took the time to tell mmm ed. Her daughter also lying cold to me. Whom was that? I've always been watched over-_-this was divergent.

Heidi - USA (27259)

Answer

Sometimes dreams can bring out reality when your mind has been clouded by some convincing person. It is best then to go with your intuition.

I hope everything works out for you. You know that you deserve the best.

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