# 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.

## List of next 15 letters

### Country

Superhero trying to outrun villan Force Affects Motion UK

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

Next 15 letters

First 15 letters

## Superhero trying to outrun villan

January 18, 2017

### Question

Hi there, I am researching for a comic book and was hoping you could answer a question I have. If an object accelerates in one direction (a) then suddenly reverses applying the same force in the opposite direction (b), is it possible that if travelling fast enough the sudden change in direction (a to b) would have a spring board effect increasing the acceleration and overall speed when continuing in direction (b)? How fast would the object need to be moving? This scene will be set in space and has a superhero character that is trying to find a way of outrunning his counterpart. Many thanks.

Karl - UK (27814)

Acceleration means that the superhero is continually increasing in speed. This could happen until he reached the speed of light.

If a the same force was applied in the opposite direction, the superhero would slow down until he stopped and then started to accelerate in the opposite direction.

It would be better to suddenly accelerate in a sideways direction, which would fool the villain, who would continue going along until he adjusts his direction of motion.

I hope that helps. Best wishes for your comic book.

## Weight of two containers of water

January 16, 2017

### Question

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.

## Calculating speed of light for spectral line

January 15, 2017

### Question

Hi,
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.

## More electrons than protons

January 12, 2017

### Question

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.

## Static electricity and combing hair

January 1, 2017

### Question

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

Thank you

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.

## Reducing static on a trampoline

December 23, 2016

### Question

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.

## Behavior of light

November 4, 2016

### Question

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.

## Charge created when rubbing materials together

October 16, 2016

### Question

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.

## Camera acts up from static electricity

October 1, 2016

### Question

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).
Thanks,
Lou

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.

## Want to know about thermal physics

September 18, 2016

### Question

I want to know more about thermal physics

tinotenda - Zimbabwe (27297)

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

## Velocity or airplane

September 1, 2016

### Question

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.

## Is electricity from burning coal static?

August 28, 2016

### Question

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.

## Wants to make an inexpensive IR detector

August 17, 2016

### Question

Sir,
Myself GAUTAM BARAIYA,
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???

Plz......help 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 Amazon.com - India - Infrared Sensors for detectors you can buy.

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

## Understanding temperature limits equation

June 16, 2016

### Question

Hi,

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.

## Difference of braking radiation and k-shell emission

May 26, 2016

### Question

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.

## Misc

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