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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 most recent 15 letters

Title

Topic

Country

Objects in contact exert force on each other Cavendish Experiment South Africa
 
Is period related to density? Pendulum India
 
Load on one wheel is greater than the others Rolling Friction and Automobile Tires USA
 
Working of drums General India
 
Why 50/60 Hz? AC Egypt
 
How does generator output 60 Hz? AC USA
 
Concerning Mossbauer effect Doppler Effect Equations for Light UK
 
What is sound? Sound USA
 
How is magnetic field created? Moving Charges Create Magnetic Field India
 
What is a solid, liquid and gas? Kinetic Theory of Matter India
 
Electric charges and protons Detection of Static Electricity USA
 
How can you change the speed? Applied Force USA
 
Breaking mass in parts Force Between Two Objects Tanzania
 
Find total beat frequency Sound Beats India
 
Are centrifugal force and inertial force the same? Inertial Force India
 

Next 15 letters

 





Cavendish Experiment

Objects in contact exert force on each other

January 14, 2018

Question

Hi Ron please clarify the following....why is it that two objects that are in contact do not exert the force of gravity on each bcz they both have mass and their centres are distance apart.

Sidanga - South Africa (28389)

Answer

When two objects are in contact, they each exert the force of gravity on each other. The main example is what an object is in contact with the Earth, where gravity between them affects them both.

But one reason it is noticeable is because the mass of the Earth is so great. If the objects are normal size, there still is an attraction, but it is almost too small to measure.

See Cavendish Experiment to Measure Gravitational Constant to see the measurement between objects.

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Pendulum

Is period related to density?

January 14, 2018

Question

Is the Time period of simple pendulum is directly proportional to density. Please explain.(while Time period does not depends on mass)

Mallikarjun - India (28390)

Answer

The period of a pendulum is independent of the mass of its bob. (See Pendulum Exhibits Periodic Motion.)

The density of the bob or weight equals its mass divided by its volume. Since the period is independent of the mass, it is also independent of the density of the bob.

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Rolling Friction and Automobile Tires

Load on one wheel is greater than the others

December 22, 2017

Question

On a 4-wheeled vehicle, is friction force from the wheels always simply additive? With a vehicle coasting on level road, I wonder if one wheel was grossly loaded much more than the other three, (say it is supporting 80% of the total weight instead of the 25% if balanced loading), the total resistive force to the vehicle would be greater. In this case, the vehicle would have more deceleration than the balanced loading condition, wouldn't it?

Wayne - USA (28362)

Answer

If there is an increased load on one tire of a vehicle, that tire will be deformed more than the others, and the rolling friction will be increased. It would be similar to having the brakes slightly applied to that wheel only.

For a front wheel, that would cause a need to adjust the steering. For a rear wheel, the differential might neutralize the difference.

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General

Working of drums

December 20, 2017

Question

working of drums and dhabela , physics of it

fatima - India (28356)

Answer

I don't have any material on the physics of drums. A good website to check on the subject is About Drums.

I hope that helps.

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AC

Why 50/60 Hz?

December 4, 2017

Question

Why is suitable frequency of AC voltage / current is 50-60 Hz?

Mohamed - Egypt (28345)

Answer

See Background of Worldwide AC Voltages and Frequencies.

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AC

How does generator output 60 Hz?

November 26, 2017

Question

In a hyydroelectric plant rushing water turns a generator, which induces an electric current. How does this get to be 60hz?

Jim - USA (28334)

Answer

The generator is set to rotate at a certain rate. Multiplying the revolutions per minute times the number of poles in the generator and dividing by 120 will give the AC frequency.

For example: 3600 rpm times 2 poles divided by 120 = 60 Hz.

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Doppler Effect Equations for Light

Concerning Mossbauer effect

November 22, 2017

Question

Just a small comment, possibly a correction. You state that in order to observe a red shift one must have the light source at high velocity.

However with Mossbauer gamma rays the Doppler shift is observable with a few mm/s velocity on the source.

Owen - UK (28333)

Answer

Thanks for pointing that out to me. I'm in the process of adding material on Mossbauer spectroscopy, including the Doppler shift at very low speeds.

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Sound

What is sound?

November 14, 2017

Question

I like sound. oh and i like waves yeah I like waves. but what is sound?

Denry - USA (28320)

Answer

Sound consists of regular vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear.

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Moving Charges Create Magnetic Field

How is magnetic field created?

November 7, 2017

Question

how megnetic field created around electric current

ravi - India (28312)

Answer

Electrical charges have an electric field around them. When the charges move a magnetic field is created perpendicular to that movement. An electric current consists of moving electrical charges.

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Kinetic Theory of Matter

What is a solid, liquid and gas?

November 7, 2017

Question

Q1. What is solid, liquids, gas

MD - India (28313)

Answer

See States of Matter for an explanation.

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Detection of Static Electricity

Electric charges and protons

November 6, 2017

Question

I was taking a Science quiz and I googled the question and your website came up. I read it and I got the question wrong. It said "electrical charges" it is actually Protons. Just in case if you want to update that. Thanks, just thought you need to know. :)

Mika - USA (28311)

Answer

Thanks for the feedback. A proton is not an electrical charge. Instead, it is a subatomic particle that HAS a positive (+) electric charge. Likewise, an electron is a particle that has a negative (-) charged particle.

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Applied Force

How can you change the speed?

October 31, 2017

Question

What are some ways you can. Change the speed

Tjey - USA (28303)

Answer

When you apply a force that pushes or pulls on an object its speed or velocity changes, provided that force can overcome friction.

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Force Between Two Objects

Breaking mass in parts

October 18, 2017

Question

a mass M is broken into two parts "m" and (M-m) related so that of gravitational between the two parts is maximum??

erickson - Tanzania (28292)

Answer

The force is proportional to m(M-m) or (mM - m^2).

If you try values of m = 0.1M, m = 0.2M, m = 0.3M, m = 0.5M, m = 0.6M and so on, you will find that the maximum value of m(M-m) is at m = 0.5M. In other words, the maximum gravitational force is when both pieces are the same size.

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Sound Beats

Find total beat frequency

October 16, 2017

Question

PLEASE SOLVE THIS QUESTION!

Three tuning forks of frequencies 200,203,207 Hz are sounded together. Find the beat frequency.

ONKAR - India (28288)

Answer

The beat frequency is the difference of two frequencies. See Beat Frequencies in Sound. For example, the beat frequency between 200 and 203 would be 3 Hz. Thus, you could have 3 different, overlapping beat frequencies.

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Inertial Force

Are centrifugal force and inertial force the same?

October 15, 2017

Question

I don't get the concept clearly. Is centrifugal force and inertial force are same?

krishna - India (28287)

Answer

An inertial force is a force that resists a change in velocity of an object. That means, it also resists a change in direction.

Since a centrifugal force is caused by a change in directions, it is an inertial force. However, accelerating an object results in an inertial force that is not a centrifugal force.

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