# Physics Feedback

by Ron Kurtus

Readers have sent in a total of 846 comments and questions on Physics issues. They are listed according to date.

## List of most recent 15 letters

### Country

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

Moving fast on a muddy road Uses of Friction India

Period when mass of string is not neglected Pendulum Equations India

Problem with spinning spaceship Artificial Gravity USA

Changing parameters in Cavendish experiment Cavendish Experiment Egypt

Why isn't the solar system a giant atom? Atom as Solar System USA

How physical conditions affect density Density Factors USA

Voltage, current, and resistance DC USA

Next 15 letters

## 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)

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.

## How is magnetic field created?

November 7, 2017

### Question

how megnetic field created around electric current

ravi - India (28312)

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.

## What is a solid, liquid and gas?

November 7, 2017

### Question

Q1. What is solid, liquids, gas

MD - India (28313)

See States of Matter for an explanation.

## 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)

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.

## How can you change the speed?

October 31, 2017

### Question

What are some ways you can. Change the speed

Tjey - USA (28303)

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

## 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)

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.

## Find total beat frequency

October 16, 2017

### Question

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

ONKAR - India (28288)

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.

## 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)

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.

## Moving fast on a muddy road

October 12, 2017

### Question

does it possible when a vehicle moves so fast in a muddy road ? does the tyre slips due to friction?

savana - India (28284)

If you accelerate the car on a muddy road, it is possible that the wheels will just start to spin. That is why the tyres need to have traction to go in muddy conditions. See Traction Friction of Tires for more information.

## Period when mass of string is not neglected

October 11, 2017

### Question

plz tell us the formula for calculating time period of pendulum when the string mass is not neglected and the mass of the bob is less the string mass?

Akash - India (28278)

It is a complex calculation.

T = 2pi*SQRT(I/mgR), where T is the period, I is the moment of inertia, m is the mass of the object, and R is the center of mass between the pivot point and the bob.

Also, I = mL^2/3, where L is the length.

## Problem with spinning spaceship

October 11, 2017

### Question

I can see a big problem where a spaceship has a spinning part as spaceship tries to make a turn. The spinning part want to go straight unfortunately the spaceship part wants to turn. It may be too much for the air seals.

a p - USA (28280)

If a spaceship was a rotating wheel or had part of it rotating, and it made a turn to change directions, it would affect the artificial gravity inside the wheel. It could be possible for one side to increase the artificial gravity, while another part lose the gravity, such that people on that dies would start floating.

The best thing for a rotating spaceship would be to stay in a straight line or be in orbit around the Earth.

Air seals would not be a factor.

## Changing parameters in Cavendish experiment

October 11, 2017

### Question

If we change
1 - Diameters of the balls
2 - masses of the balls
3 - metals of the balls
4- L torsion bar length
if you change the previous parameters will G still constant factor???!!!

Anwer - Egypt (28281)

You can change the parameters and perform the Cavendish Experiment to get the value of the gravitation constant G. However, the values need to be optimized to get the most accurate result. For example, if the masses of the balls were decreased, the resulting value for G would not be as accurate and there might be some errors in the measurement.

## Why isn't the solar system a giant atom?

October 5, 2017

### Question

I had a question about the article you wrote regarding Bohr's Model of an atom. Why do you disagree with the fact that our solar system can't be just one "giant" atom. I was hoping to get in touch with you to discuss this?

Tristan - USA (28273)

Although our solar system looks like it could be a giant atom, there are a number of problems in the analogy. One it that electrons in an atom have an electrical charge, while there is nothing similar in the solar system. Also, the nucleus of an atom is made up of protons and neutrons, while the Sun is a mass of hot gases.

On the quantum scale, atomic particles are not tiny spheres but are wave packets.

Still, the similarity between the solar systems and atoms is intriguing.

## How physical conditions affect density

September 30, 2017

### Question

Describe how physical conditions affect density

kiprotich - USA (28267)

Density is mass divided by volume. Compressing an object decreases its volume and thus increases its density.

## Voltage, current, and resistance

September 27, 2017

### Question

1. in a dc circuit is the ratio of voltage to current equal to the resistance?

ijagbemi - USA (28262)

According to Ohm's Law for Simple Electrical Circuits, V = IR or V/I = R, where V is the voltage, I is the current, and R is the resistance.

## Misc

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