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Physics Feedback

by Ron Kurtus

Readers have sent in a total of 775 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 most recent 15 letters




Weight of two containers of water Floating Egypt
Calculating speed of light for spectral line Doppler Effect Equations for Light Ireland
More electrons than protons Electrostatic Induction Phillippines
Static electricity and combing hair Electricity Canada
Reducing static on a trampoline Reducing Static Electricity Shocks USA
Behavior of light Visible Light Philippines
Charge created when rubbing materials together Electrostatic Induction Pakistan
Camera acts up from static electricity Reducing Static Electricity Shocks Canada
Want to know about thermal physics General Zimbabwe
Velocity or airplane General USA
Is electricity from burning coal static? Basics of Static Electricity Australia
Wants to make an inexpensive IR detector Infrared Radiation India
Understanding temperature limits equation Temperature Limits Equations Brazil
Difference of braking radiation and k-shell emission X-ray Generation Cambodia
Ways to improve site AC USA

Next 15 letters



Weight of two containers of water

January 16, 2017


Two containers one of them has water and small piece of wood and another one has only water which one is heavier ?

Misho - Egypt (27810)


If both containers have the same amount of water in them, then the one with the wood in it would be heavier by the weight of the wood.

However, if the containers were full to the top and the piece of wood was added to one of them, some water would overflow from the container. The weight of the overflow water would be the weight of the water displaced, such that both containers would then weigh the same.

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Doppler Effect Equations for Light

Calculating speed of light for spectral line

January 15, 2017


Hope you can help us. We are trying to calculate the velocity of a wavelength using a line profile.
We don't know what we are doing :-(
We know the rest wavelength 36.4680 nm, the line centre is 36.462 nm and c.
The anwser we are getting is 299785064.75!!!
Can the velocity of the wavelength be near the speed of light?
What is the correct formula?

Thank you on behalf of the LYIT astronomy society.

Seamus - Ireland (27806)


You need to be exact in your terminology. The "velocity of a wavelength" is incorrect. You should be looking at the velocity of light for a given wavelength.
In space, the light travels at the same speed for all wavelengths. When the radiation is passing through a material, the speed varies according to the wavelength or frequency.

If the source of the light is moving, the speed of light remains constant, but the wavelength can shift according to the direction and velocity of the source.

The profile of a spectral line is affected by the various velocities of the particles emitting that specific wavelength. The Doppler Effect causes the slight shifts in wavelength from the ideal situation.

I hope that helps.

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Electrostatic Induction

More electrons than protons

January 12, 2017


what is the overall charge of an object that has 18 more electrons than protons?

jeffrey - Phillippines (27799)


Negative ions may have a few more electrons than protons. It would be very unusual to have 18 more electrons than protons. However, since electrons have a -1 charge, the overall charge of the object would be negative 18 or -18.

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Static electricity and combing hair

January 1, 2017


Why would it be better to comb hair with aluminum comb rather than plastic comb to avoid build up of static charge?

Thank you

Sam - Canada (27770)


Human hair and aluminum combs both tend to give up electrons, while a plastic or hard rubber comb attracts electrons and thus attracts the hair. See Materials that Cause Static Electricity.

Also see Controlling Flyaway Hair from Static Electricity.

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Reducing Static Electricity Shocks

Reducing static on a trampoline

December 23, 2016


My trampoline has a safety net surrounding it.I put my water hose on jet spray and cleaned the net.That got rid of the static instantly. Now the kids can play on it in peace. The accumulation of dust on the screen was the problem.

Ernestine - USA (27578)


Thanks you for your information on solving the problem of build-up of static electricity on a trampoline.

I am sure our readers will appreciate knowing about your method.

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Visible Light

Behavior of light

November 4, 2016


Give one of your observations on the behavior of light and tell which theory of light supports this behavior.

Jesus Ramon Neopolo - Philippines (27448)


See Visible Light for a list of properties.

Both the wave theory of light and the corpuscular theory of light support the behavior.

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Electrostatic Induction

Charge created when rubbing materials together

October 16, 2016


What charge will be created on following bodies when we rub them against each other
1-metal vs metal
2-insulator vs insulator
3-metal vs insulator

israr khan - Pakistan (27384)


Much depends on which metals and insulators are used. See Materials that Cause Static Electricity for a list of materials and how well they attract or give up electrons.

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Reducing Static Electricity Shocks

Camera acts up from static electricity

October 1, 2016


It seems that static electricity from my body is causing my camera to crash(freeze) and my viewfinder and screen to function abnormally (become pixelated with flashing bands of colour). Does this make sense? If so what can I do? (Photography is my serious hobby).

Lou - Canada (27339)


It is unusual but certainly possible that excess static electricity is causing problems with the electronics in your camera. One thing you can try is to ground yourself before trying to take a picture by touching some metal object. Also, try to avoid polyester clothes when taking pictures. Dry skin on some materials can create static electricity in your body.

I hope these ideas help. Let me know how things turn out. And best wishes with your hobby.

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Want to know about thermal physics

September 18, 2016


I want to know more about thermal physics

tinotenda - Zimbabwe (27297)


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

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Velocity or airplane

September 1, 2016


A plane flying at 120mi/h at an altitude of 15,000ft. It is 27 minutes ahead of its schedule arrival time what is its velocity?

Brittany - USA (27260)


If the plane is flying at 120 mi/hr, that is its velocity. Its altitude and schedule aren't necessary. Also, it would be good to know how far it is flying.

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Basics of Static Electricity

Is electricity from burning coal static?

August 28, 2016


hi, my science teacher and i have recently had an argument about whether or not the electricity generated by burning coal is static as it is a copper brush rubbing on a magnet. he thinks this is not so. i disagree. please settle our dispute

Wyatt - Australia (27242)


Of course burning coal can be used to boil water to turn a generator and create AC or DC electricity. The rotating generator could also be used to create static electricity with a device like a Wimshurst electrostatic generator.

But also, when coal burns, the movement of air from the fire can create static electricity in the air. But I don't think that is what you were talking about.

I hope this helps clarify your discussion.

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Infrared Radiation

Wants to make an inexpensive IR detector

August 17, 2016


I have just passed out 12th science

I am interested in infrared rays ...I want to make infraread detection device which has very low cost that is cheaper...Will you plz guide me for the same..

Will you introduce me with some infrared detection device which we get from market??

Does animal like dog and pig emite infrared rays??? me....

Gautam - India (27217)


Yes, people and animals emit infrared rays. Night-sight cameras and goggles can show their heat pattern.

The Herschel Infrared Experiment can show a simple way to demonstrate the effect if infrared. That may give you some ideas.

You might be able to adapt your digital camera to detect infrared, as shown in Infrared Imaging and Two Science Experiments.

Also check - India - Infrared Sensors for detectors you can buy.

I hope this helps. Best wishes for success in your projects.

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Temperature Limits Equations

Understanding temperature limits equation

June 16, 2016



I need to know about it 3mc² / 2k, I want to complete it. where I study?

DOUGLAS - Brazil (27083)


The temperature of an idea gas is related to velocity: T = 3mv²/4k. When the velocity of the particles approach the speed of light, the equation changes to T = 3mv²/4k. (See Equations for Temperature Limits). Details can be seen at Kinetic Temperature.

But note that there are several other theories related to the maximum temperature, including the Theory of Relativity.

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X-ray Generation

Difference of braking radiation and k-shell emission

May 26, 2016


1. The different of braking radiation and k-shell emission?

2.The electromagnetic applications in medicine?

sathya - Cambodia (27028)


Braking x-ray radiation (Bremsstrahlung) is the continuous distribution of x-rays which forms the base for the two k-shell peaks. See Characteristic X-Rays for details.

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Ways to improve site

May 5, 2016


It's better if you could index the questions you receive cause they are very nice and seen some using the blog link.It helps users to get around different types of questions of their favourite subjects like given here:

Also I have noticed that while searching for Electricity Generation I could see a page in the search but couldn't see any link in the website that tells about electricity generation.

Justin - USA (26981)


I'm trying to have a better organization of Feedback Questions. Right now, all the feedback on Electricity are lumped together. I want to get the feedback per subject.

Using our search box at the top of the pages, I search "Electricity Generation". The first entry was "Generating Electrical Current" on the site. Perhaps you missed it.

Anyway, thanks for your feedback and suggestions that will help improve the site.

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