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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 16076 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





When rocket thrust is reduced Gravity USA
What is efficiency? Machines USA
Relationship between Brownian motion and Kinetic theory Physics Matter USA
Branches of Physics Physics Kenya
Suggested resource Security USA
Velocity equations Physics Gravity India
Applying a force Force Philippines
Vectors in friction Friction USA
Confusion about inertia Force India
Separation from time interval Sound USA
Details on starting a business Entrepreneurship Nigeria
Designing back cover Publishing India
Contact surface in rollers Machines Pakistan
Suggested resource Career Germany
Loudness of sound under water Sound Papua New Guinea

Next 15 letters


When rocket thrust is reduced


July 20, 2019


Could you also please address what happens if at 20m/s, the rocket thrust is reduced and maintained to exactly balance gravity?

Obviously we ignore other gravities, air resistance, etc.

It is my opinion that when thrust = gravity, velocity remains constant and all thrust energy is converted to potential energy.

Mike - USA (29117)


Once the rocket thrust is reduced to simply balance the force of gravity, the rocket will continue at 20 m/s (assuming no air resistance).

Since the potential energy of the rocket with respect to gravity is simply PE = mgh, where "h" is the altitude, PE will increase PE will increase at a constant rate and the thrust energy is converted into that PE.

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What is efficiency?


July 12, 2019


What is efficiency?

Aeesha - USA (29104)


The efficiency of a machine indicates how well its input energy is converted to useful output energy or work. In other words, efficiency is the output work divided by the input work.

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Relationship between Brownian motion and Kinetic theory


July 9, 2019


What is the relationship between Brownian motion and the Kinetic Theory of Matter?

Your content is rich on the topic.

Emmanuel - USA (29098)


The Kinetic Theory of Matter states that matter is composed of a large number of small particles—individual atoms or molecules—that are in constant motion.

On the other hand, Brownian motion is the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium. Thus Brownian motion concerns the collisions of particles in motion due to the Kinetic Theory of Matter.

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Branches of Physics


July 8, 2019


What are the branches of Physics?

kevin - Kenya (29096)


Branches of Physics include:

- Classical physics
- Modern physics
- Nuclear physics
- Atomic physics
- Geophysics
- Biophysics
- Mechanics
- Acoustics
- Optics
- Thermodynamics
- Astrophysics

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Suggested resource


July 5, 2019


Happy Friday!

My name is Felicia, and I volunteer in a Job Corps program for inner-city youth that has decided to enter our program to better themselves. They are doing this by learning a trade that will allow them to enter the workforce with a real skill set. I am writing on behalf of one of my students, Anthony, who is involved in our Network Cable Installation program. Anthony will be finishing the program soon, so he's been assigned a project to match resources with websites that future classes that include all of the jobs that kids in our program can pursue after they complete the program. While helping him with this project, we came across your website We want to say thank you for providing us with all your helpful information.

Anthony has already lined up a job with a well-known home security firm to install security systems in new residential construction and he is incredibly excited about it. In his research, he found this useful article about choosing a security camera system, and while the article alone is useful, what he really got excited about was the information on how to set up a security camera system after the install has actually been completed. Here is the article he found -

To graduate, he needs to show that he helped share information with others that could find his research useful. With this requirement in mind, would you please add a link to the article he found to your own website with all your other useful links? He's been having some trouble with the exercise and it has really been weighing on him. I'd like to surprise him with this and put his mind at ease that he'll be able to complete the program and take on the next chapter in his life. He has worked very hard at this and I am incredibly proud of him. Would you please add it for him?

Thank you again and thank you for your consideration.

Felicia - USA (29094)


Thanks for the resource. I added a link at Security Resources - Systems.

Best wishes for Anthony's success.

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Velocity equations


June 17, 2019


Would you please Explain the sign convention of g with the following examples

A)A ball thrown vertically upwards from the ground.
B)A ball thrown vertically upwards from a tower of hight h.

Find the maximum hight, find the time of flight and also velocity of ball before it reaches the ground.

S - India (29073)


The acceleration due to gravity (g) is positive toward the ground. When an object is thrown upwards, the force of gravity slows the velocity of the object.

See Gravity Equations for Objects Projected Upward..

To find the maximum height, you need the initial velocity upwards of the object, as well as the height from which it is thrown. The same is true for the time in flight.

Also see: Equations for Objects Projected Upward

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Applying a force


June 12, 2019


When you apply the force, does it means there's a motion all the time ? And explain.

Norjanah - Philippines (29065)


When you apply a force on an object, that force must overcome any friction that prevents the object from moving. Once the force is greater than the resistance from friction or other resistance, the object will move.

If there is no friction holding the object back, it will move freely and accelerate according to F = ma.

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Vectors in friction


June 10, 2019


The frictional force can be represented as a vector in the direction of motion of an object on a surface. The normal force can be represented as a vector perpendicular to surface of the object. The usual equation is f = mu N. But when a vector N is multiplied by a number (mu) the result is another vector f of a different magnitude than the normal force but in the same direction. But the normal force is perpendicular to the frictional force. How is this possible? Please explain.

Robert - USA (29063)


The resistance due to friction is in the opposite direction of the motion of the object. Multiplying the normal vector N by a scalar number (mu) does not change the normal force. For example, if N was the weight of an object, changing the coefficient of friction (mu) would not change the weight.

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Confusion about inertia


June 3, 2019


If a body of mass m is accelerated with acceleration 'a 'then force is na and inertia force also _ma ,so resultant force is zero then how body accelerated?

Abhishek - India (29060)


The concept can be confusing. The inertial force is simply what is felt and does not affect the resultant force.

I updated the Inertial Force page to help clarify the concept. I hope that helps.

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Separation from time interval


June 1, 2019


Two men stand a distance apart besides a long metal fence on a still day. One man places his ear against the fence while the other gives the fence a sharp knock with a hammer. Two sounds separated by a time interval of 0.5s are heard by the first man. If the velocity of sound in air is 330m/s and in the metal 5280m/s, How far apart are the men?

Moses - USA (29057)


You have to use some Algebra to solve the problem.

Let d equal the separation. Also d = v*t. The time for the sound to travel in each medium is t1 = d/v1 and t2 = d/v2.

If the time interval is (t1 - t2) = 0.5 s, then 0.5 = (d/v1 - d/v2) = d*(1/v1 - 1/v2), and d = 0.5*v1*v2/(v2 - v1)

Substituting v1 = 330 m/s and v2 = 5280 m/s in the equation will result in the separation.

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Details on starting a business


May 27, 2019


I need full details on how to start my own business.

Abdulrasheed - Nigeria (29052)


First of all, you need to define what sort of business you want to start. Do you want to sell a product or a service?

It is always good to start small before seeking investors in your business. Also, it is good to get others interested in your ideas.

Go through the lessons in

and also check many of the resource websites at:

Best wishes for success in starting and running your business.

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Designing back cover


May 21, 2019


Please suggest or design a book cover back cover or spine cover of a book based on the story:
A boy scores bad marks in class X and left his home.
After passing some years wandering here ad there he joins a assistant magician to a group.
He marries with the daughter of head magician
He wants His children should do further study and should not join as a magician.
The theme : Importance of Education

Dr Rajesh - India (29048)


First of all, you need a catchy title for your book that will get readers interested in it. Then on the back cover, under the title you need to have a few sentences that will summarize and create more interest. For example: "This book shows how a father wants to teach his children from the lessons learned from not having a good education."

You can then list highlight points from the book and perhaps comments from people who read your book.

Go to a bookstore or library and study the back covers of similar books.

Best wishes in writing, designing, and publishing your book.

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Contact surface in rollers


May 20, 2019


As the friction does not depend upon the surface of contact then how rolling reduces the friction?

Abdur - Pakistan (29046)


If you consider sliding an object across the ground, you can see that using rollers or wheels results in much less friction.

The only friction in using rollers is due to a slight "stickiness" an the contact surface. But this is negligible.

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Suggested resource


May 18, 2019


Hey School for Champions Editors,
I was doing some research on interview tips and noticed that you have this killer resource page on your site: . Awesome job!

Since you’re clearly an authority on the subject, I thought you’d be interested in checking out my article on "Best Interview Practices for Job Seekers". It’s super in-depth and I think it would make an awesome addition to your resource page (especially as your readers would love and benefit from it immensely).

Here’s the link if you’d like to check it out:

CEO Cleverism

Martin - Germany (29042)


Thanks for the suggested resource. I added a link at

Best wishes for success in your work.

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Loudness of sound under water


May 14, 2019


Is the loudness of sound greatest in water than it is in air

Willie - Papua New Guinea (29037)


The loudness or amplitude of a sound under water seems louder than in air. One reason is that in air, only your eardrum detects the sound. However, under water, your eardrum and your skull sense the sound. Also, sound travels faster under water.

You can test the loudness by comparing a sound from the clicking objects together above water and doing the same under water with your head also under water.

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