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Physics Feedback

by Ron Kurtus

Readers have sent in a total of 853 comments and questions on Physics issues. They are listed according to date.

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

List of next 15 letters




Device using small disc magnet General Canada
Electrostatic induction and rice General India
Reflecting sound from concrete wall Sound and Obstacles India
Would the Gravity book be helpful? Work Against Gravity USA
What if matter did not change its state? Changing States of Matter Pakistan
Is pressure distributed on a bench? Pressure USA
Permission to use images Pressure and States of Matter USA
Where are the attractive forces equal? Force Between Two Objects USA
Connecting AC to terminals of a battery AC India
Why aren't mercury lamps used more often? Lighting India
Where do charges go? Basics Zimbabwe
Wants to know about particle physics General USA
Viewpoint on gravitation and Big Bang theory General Bangladesh
Solenoid and electromagnet Solenoids India
Give examples of using force Forces Malaysia

Next 15 letters


First 15 letters


Device using small disc magnet

September 6, 2017


Good morning Ron. My son and I are developing a low tech medical device that relies on the attraction between a small disc magnet 20 mm x 2 mm and a similarly sized flat washer. We're having a problem with the amount of attraction between the two and need to increase it and are thinking about increasing the size of the magnet or the washer but are constrained in doing this due to physical dimensions. Is there anything readily available such as a flat washer or disc with a higher than normal iron content that would cause the magnet to be more strongly attracted to it? Many thanks!

Niall - Canada (28214)


You might try a Neodymium disc magnet. They are small, strong and inexpensive and can be bouht through or other outlets.

I hope that helps. Best wishes for success with your device.

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Electrostatic induction and rice

September 5, 2017


Hello sir...

Electrostatic induction or electrostatic generator that can stick with plain dry rice or not ???

daksha - India (28213)


An example of rice being affected by static electricity can be explained in Rice grains sticking to a polythene bag.

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Sound and Obstacles

Reflecting sound from concrete wall

September 3, 2017


what frequency can a concrete or a stone reflect back.

Kapil - India (28210)


Within the range of human hearing (20 Hz - 20,000 Hz), the higher frequencies are reflected much better than the lower frequencies. Of course, much depends on how smooth the concrete surface is.

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Work Against Gravity

Would the Gravity book be helpful?

September 1, 2017


Hi, I will be working on a physics project this fall semester and was wondering if your book would be helpful in assisting with the project and/or project ideas.

Thank you,

Ashley - USA (28207)


The advantage of the book is that everything is in one place, such that it is easier to navigate. However, all the material on Gravity and Gravitation is on the website. You can pick and choose what you want to see.

Best wishes for success in your Physics project.

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Changing States of Matter

What if matter did not change its state?

August 25, 2017


Explain that what happened if there would be no change in states of matter?


Aamish - Pakistan (28197)


If all matter stayed in its existing state or phase, ice would not melt to become water, and water could not boil into steam. Also, there would be no evaporation of water. Just these factors alone would affect living beings in a short time.

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Is pressure distributed on a bench?

August 15, 2017


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)


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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Pressure and States of Matter

Permission to use images

August 14, 2017


I would like to use the phase diagram figures that you have on this page:

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)


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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Force Between Two Objects

Where are the attractive forces equal?

August 5, 2017


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)


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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Connecting AC to terminals of a battery

July 26, 2017


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

Krishna Priya - India (28141)


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?

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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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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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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Solenoid and electromagnet

June 13, 2017


Why solenoid is used for making electromagnet

Nishant - India (28091)


A solenoid is an electromagnet without the iron core in it. The solenoid can be used to pull a core inside it.

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Give examples of using force

June 12, 2017


Name one examples when force can stop motion.

Name one examples when force can change the shape and size of an object

Nicholas - Malaysia (28088)


You can push on a rolling cart to stop its motion.

You can compress a foam rubber ball to change its size and shape.

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Next 15 letters


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