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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 15974 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





Suggested resource Animal Health USA
Fuel needing for Lunar Lander Gravitation South Africa
Biology vs Physics Physics USA
Output work Machines Nepal
Suggested resources Aging USA
Dropping a feather and steel ball Gravitation Australia
Experiments in static electricity Static Electricity Australia
Term for temperature when matter changes Matter USA
117 V motor powered by 240 V Electricity UK
Wands free books on EMF Physics Magnetism Ethiopia
Review Gravity book Gravity USA
References on storing electrical power Electricity Germany
Output distance fir workbench Machines USA
Timeline of the development of chemistry Chemistry Philippines
Questions on printers Publishing Pakistan

Next 15 letters


Suggested resource


July 16, 2018



I'm a substitute science teacher for Jefferson Elementary school. I've been teaching my summer students on how dangerous black mold can be around animals. I just wanted to send you a quick email. We came across your page and found it useful.

My kids and I wanted to send you back another page we found that included a page about black mold affecting cats. We thought you might want to add it your site because it explains it pretty well. Here it is:

Would you be able to consider adding a link to the page they found on your site for them? I'd love to show them that reaching out works. They would be so excited!

Thank you in advance.

Samantha - USA (28631)


Thanks to your class for the resource on how mold in the house can affect cats. I added the link to the Animal Health Resources page.

Best wishes for the success of your students.

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Fuel needing for Lunar Lander


July 15, 2018


Ron, Thanks for a great article! Somewhere in my engineering training I never learned the space physics! Have you also made similar calculations for the lunar lander to get away from the moon with its full payload? Do you know what fuel it used? If memory serves me correctly hydrogen contains about 140 MJ/kg. We can thus from your energy calculation deduct how much fuel the lander needed to carry in order to stop at zero velocity from the probable 32000km/h speed of the approaching orbiter, then taking off and rendezvous with the command station.

Naas - South Africa (28629)


In Escape Velocity from Gravity, I show the escape velocity from the surface of the Moon. However, that is an approximation and does not take into account the weight of the Lunar Lander.

Right now, I don't have details and specifics on accelerating a rocket from the surface of the Moon. It can get pretty complex.

As far as the fuel goes, Wikipedia states: "The Ascent Propulsion System (APS) or Lunar Module Ascent Engine (LMAE) is a fixed-thrust hypergolic rocket engine developed by Bell Aerosystems for use in the Apollo Lunar Module Ascent Stage. It used Aerozine 50 fuel, and N2O4 oxidizer."

I hope that helps. Best wishes for success in your studies.

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Biology vs Physics


June 19, 2018


Hi. I am 14 and I’m in 8th grade. I finished middle school this year. And this fall I will be in high school. Next semester I will be taking biology is it harder than physics ?

Zoe - USA (28590)


Biology often consists of many fact about the various plants and animals. Physics often includes math and equations.

Typically, Biology is offered in the sophomore year in high school, while Physics is taken in the senior year. Both are interesting subjects and are worth taking.

Best wishes for success (and fun) in high school.

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Output work


June 19, 2018


In a machine a load of 3000N is lifted by 500N effort if the load travels a distance of 2m & effort travels a distance of 16m calculate
Ma, VR input work output work & efficiency

Krishtina - Nepal (28591)


There are three types of mechanical advantage: Distance, Force, and Speed. See Mechanical Advantage.

Force MA would be 3000/500 = 6.

Work is force x distance moved. Input work = 3000N x 2m.

If there are no losses due to friction, Efficiency = output work/input work.

I hope that helps.

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Suggested resources


June 15, 2018


Every 11 seconds, another senior has been treated in the emergency room for a fall-related injury. That statistic recently hit home for me personally when my dad fell last summer. So, I and a few others at Always Discovering have been focused putting together some resources on fall prevention ever since.

My dad was lucky and recovered quickly. Then, my sister and I came in and made some changes to his flooring and bathroom and gave him a personal alarm, which, of course, he hates. :). There was a bit of a learning curve for me and pages like yours here really helped a lot.

So I’ve prepared a Fall Prevention Toolkit. I hope it will help you the way it’s helped me.

Thank you,

Angie - USA (28588)


Thanks for the suggested resources. I added the links in Aging Resources - Fall Prevention.

Best wishes for success in your work.

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Dropping a feather and steel ball


June 13, 2018


I have a problem with the feather and steel ball falling in a vacuum. It seems that the mutual attraction between the two heavy objects (ball and earth) will be greater than between the feather and earth, so shouldn't the ball fall faster?

Ian - Australia (28587)


The Equivalence Principle of Gravity states that the objects should fall at the same rate. However, this is really an approximation, using the acceleration due to gravity (g) as a constant.

The equation for the force between two objects presents the true picture. But when the objects are close to the Earth, and the masses are small compared to the Earth, they will fall at close to the same rate. However, if the steel ball is very heavy, you could see a slight difference in the rate of falling.

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Experiments in static electricity

Static Electricity

June 7, 2018


I am working on a project which needs to make surface of negatively charged plastic (mostly made of acrylic) to positively charged surface. can you help me how I can do this? it should be noted my surface is not accessible and we can just inject solution by microsyringe.

Sepideh - Australia (28576)


I'm sorry, but I'm really not sure how you can do that. Negatively charged plastic material could be made close to neutral but probably not positive.

Best wishes for success in your project. Let me know how it turns out and what solution you came up with.

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Term for temperature when matter changes


June 7, 2018


Is there a term for the temperature which matter changes? I have heard a generally term and cannot recall it. Thank you

David - USA (28577)


Threshold temperature is often used for the temp when matter changes. There may be some other terms also used for the effect.

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117 V motor powered by 240 V


June 1, 2018


Can a motor rated at 117v 60hz be used with 240v 50Hz without a converter and without damaging it? Thank you.

David Edwards

David - UK (28572)


The 240 V input would probably overheat and burn out the motor rated at 117 V. The frequency difference is not a factor.

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Wands free books on EMF


May 30, 2018


Hello I am bereket, age 20 and I'm from Ethiopia. I want to ask you how I can get free online books on EMF.

Bereket - Ethiopia (28571)


There are some free downloads on EMF from Free Books - EMF.

I'm not sure how extensive they are, but they might give you what you want.

Best wishes for success in your studies.

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Review Gravity book


May 29, 2018


Hello Ron,
I was wondering if you would be interested in reviewing my new book, "Taking on Gravity: A Guide for Practical Gravitation." I would be willing to send you a free book for review in exchange for one of your books. I would review your book as well on a site of your choice. I think you will find this book very interesting. Hope to hear back from you soon.

Richard - USA (28569)


I'd be glad to review your new book on Gravity. Instead of going through the hassle of mailing the book, do you have an electronic version: Kindle, EPUB, or PDF? That would be more convenient.

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References on storing electrical power


May 28, 2018


Hello there,

My name is Daniel OConnell and I'm extremely passionate and interested in sustainability and power.

Who am I in a professional sense? Not really anyone important. However, with what I lack in certification I excel in commitment and hard work.

The reason why I am messaging you is that I read your interesting view in storage of electrical power specifically using static means. The Leyden jar.

I'm wondering if you have any research or other documentation regarding this topic. I would like to create a prototype that solves humanities issue or storing power. I know it sounds ridiculous. However, with some inventions I've been working on I really think there are possibilities in this space.

Is this something you can help me with?

Kind regards,

Daniel - Germany (28568)


Static electrical charges can be stored in a Leyden jar. However, since it is a very simply system, the amount of power is limited. The next step up is to use capacitors--which are really complex Leyden jars.

An interesting article on this is: Can capacitors in electrical circuits provide large-scale energy storage?.

Also see: Can Supercapacitors Surpass Batteries for Energy Storage?.

But in general, large batteries and other methods are commonly used for Electricity Storage.

I hope that helps. Best wished for success in your efforts.

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Output distance fir workbench


May 27, 2018


As a preamble, I'm in the process of building a wood shop workbench with hidden tools. (router, table saw, planner) i.e. when I press a button my tools rise up out of the bench. I've experimented with scissor lifts and winches, but now I'm liking your idea of using a Class 3 lever powered by a linear actuator.

Increasing Distance with a Lever

Now to my question: if DO/DI = do/di, I get DO = (do/di)xDI. Plugging in some numbers using do =67, di =20 and DI =52, I get DO = 174.2. My confusion is, in a class 3 lever, how can DO be significantly greater than do?

Thank you,
John M Hine, MD

John - USA (28566)


You are really looking at having a mechanical advantage, where the output distance (DO) is much greater than the distance of the output to the fulcrum (do). See Distance Mechanical Advantage for more information.

Off hand, I would think a screw configuration might work better than an lever.

Best wishes for success in makig your workbench. Let me know how things turn out.

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Timeline of the development of chemistry


May 25, 2018


Timeline of the development of chemistry

Jesus Ramon Neopolo - Philippines (28565)


You can an extensive list at Chronology of Major Events in Chemistry.

Another good listing is Timeline of Chemistry.

I hope that helps. Best wishes for success in your studies.

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Questions on printers


May 22, 2018


Qno1: Difference between IPACT and NON IMPACT printers?

Qno2: which printers produce coloured output and write their features?

Qno3: why the page that comes out of the thermal printers is hot?

Aamish - Pakistan (28558)


Impact printer refers to a class of printers that work by banging a head or needle against an ink ribbon to make a mark on the paper. This includes dot-matrix printers, daisy-wheel printers, and line printers.

Most modern printers, including inkjet and laser printers, don't include an ink ribbon and are considered to be non-impact printers.

Some laser and inkjet printers can print in colours.

Thermal printing (or direct thermal printing) is a digital printing process which produces a printed image by selectively heating coated thermochromic paper, or thermal paper as it is commonly known, when the paper passes over the thermal print head. Since the special paper is heated, it can come out hot.

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Next 15 letters


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