# Physics Feedback

by Ron Kurtus

Readers have sent in a total of 886 comments and questions on Physics issues. They are listed according to date.

## List of most recent 15 letters

### Country

Resolve components Mechanics Nigeria

Reducing friction Friction USA

Calculating simple pendulum Pendulum Equations Nigeria

Sound of sea is louder at night Sound Pakistan

Role of moons in theory Atom as Solar System India

Moving the magnetic field Generating Electricity USA

Relationship between Brownian motion and Kinetic theory Kinetic Theory of Matter USA

Branches of Physics General Kenya

Velocity equations Convention for Direction in Gravity Equations India

What are quarks? Matter Sudan

Properties of good insulators General USA

Doppler effect Visible Light India

Time to reach the ground Derivation of Velocity-Time Gravity Equations India

Confusion on thermal energy Thermal Potential Energy USA

Static charges and slugs Static Electricity Shocks UK

Next 15 letters

## Resolve components

January 2, 2020

### Question

How can I get your materials, how can I know how to resolve component, the understanding

Okesanjo - Nigeria (29306)

What are you trying to do concerning this subject?

## Reducing friction

December 20, 2019

### Question

I'm doing a project to how to reduce friction, so how do you reduce friction?

sameera - USA (29300)

See Reducing Sliding Friction.

Also see Friction Experiments.

Best wishes for success in your project.

## Calculating simple pendulum

November 20, 2019

### Question

what is the method of calculating simple pendulum

MAUAN - Nigeria (29272)

You can measure the frequency that a pendulum swings with a stopwatch.

To calculate the frequency, you must measure the length of the rod or wire and use the equation: f = [SQRT(g/L)]/2PI.

(See Equations for a Simple Pendulum.

## Sound of sea is louder at night

October 8, 2019

### Question

Why sound of sea is louder at night than day time???

Nahida - Pakistan (29214)

The loudness or amplitude of sound increases with a reduction in temperature. The air above the sea is cooler at night and thus seems louder.

See Sound Seems Amplified Over Water for an explanation.

## Role of moons in theory

September 9, 2019

### Question

1 how would the moon plays role in the given theory?
2 what would change in the theory if e considered 9 planets?
Or change to 12 planets?>

majid - India (29165)

The Solar System model of an atom looks at electrons moving around the nucleus of the atom. However, in most solar systems, many planets also have one or more moons revolving around the planet. This presents a problem with this model, since electrons are primary particles that cannot be subdivided.

Also, according to Quantum Mechanics, the sub-atomic particles can be viewed as wave-forms.

Thus, this model is simply convenient way of looking at the Solar System.

## Moving the magnetic field

August 16, 2019

### Question

I'm a tutor. Discussing electricity with students. This came up. If you move the field around the coil, instead of the coil moving, would that generate a current? Thank you!

james - USA (29151)

The first illustration in Generating Electrical Current shows a wire moving through a magnetic field. You could easily move the magnets and keep the wire stationary for the same effect.

## Relationship between Brownian motion and Kinetic theory

July 9, 2019

### Question

What is the relationship between Brownian motion and the Kinetic Theory of Matter?

Your content is rich on the topic.

Emmanuel - USA (29098)

The Kinetic Theory of Matter states that matter is composed of a large number of small particlesâ€”individual atoms or moleculesâ€”that are in constant motion.

On the other hand, Brownian motion is the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium. Thus Brownian motion concerns the collisions of particles in motion due to the Kinetic Theory of Matter.

## Branches of Physics

July 8, 2019

### Question

What are the branches of Physics?

kevin - Kenya (29096)

Branches of Physics include:

- Classical physics
- Modern physics
- Nuclear physics
- Atomic physics
- Geophysics
- Biophysics
- Mechanics
- Acoustics
- Optics
- Thermodynamics
- Astrophysics

## Velocity equations

June 17, 2019

### Question

Would you please Explain the sign convention of g with the following examples

A)A ball thrown vertically upwards from the ground.
B)A ball thrown vertically upwards from a tower of hight h.

Find the maximum hight, find the time of flight and also velocity of ball before it reaches the ground.

S - India (29073)

The acceleration due to gravity (g) is positive toward the ground. When an object is thrown upwards, the force of gravity slows the velocity of the object.

See Gravity Equations for Objects Projected Upward..

To find the maximum height, you need the initial velocity upwards of the object, as well as the height from which it is thrown. The same is true for the time in flight.

Also see: Equations for Objects Projected Upward

## What are quarks?

April 30, 2019

### Question

Physics
What are the quarks ,and did it found before or after the (the Big Bang Theory).

A quark is a fundamental or elementary particle of matter that is part of such particles as protons and Neutrons. See Fundamental Particles of Matter.

Quarks were discovered around 1968.

The Big Bang Theory was proposed around 1929, although there were other similar theories many years before that.

## Properties of good insulators

February 1, 2019

### Question

what are some good properties of good insulators.

ruben - USA (28933)

Certainly, a good insulator should hinder outside heat transfer (hot or cold). But also, the insulator must not weigh too much or take up too much space.

## Doppler effect

January 31, 2019

### Question

What will happen if object travels at half the speed of light. Is doppler effect applicable for electromagnetic waves?

Pankaj - India (28930)

An object must travel at about 90% the speed of light for any noticeable effect. See Speed of Light for information.

Also see Doppler Effect Equations for Light.

I hope that helps your understanding.

## Time to reach the ground

January 27, 2019

### Question

I have seen an equation to calculate time of an object to reach the ground as
t=?2h/g

Srinivasan - India (28924)

The time it takes a falling object to reach the ground is t = SQRT(2h/g) where h is the height or distance to the ground.

See Gravity Time Equations for Falling Objects for information.

I hope that helps.

## Confusion on thermal energy

January 15, 2019

### Question

My question is the following:

It has to do with the idea of thermal energy being a sum of both the kinetic and potential energy of a material. Because I am teaching 8th grade Science at the time, I am trying to keep this as simple as possible. However, a student asked if two samples of air (one at approx. 0 Celsius, and the other at approx 27 Celsius) have different amounts of potential energy? After reading more about it, my thought would be no, they would have the same potential energy, just different amounts.

Rebecca - USA (28916)

The definitions of thermal kinetic energy and potential energy can be confusing. I updated the whole section to try to clarify issues and make it easier to understand.

What is called Internal Energy is the sum of the Thermal Kinetic Energy and Thermal Potential Energy.

See the updated versions of Thermal Energy is Kinetic Energy and Thermal Potential Energy.

The potential energy of two sample of air at different temperatures would be approximately the same. However, since the atoms or molecules travel faster at the higher temperature, the kinetic or thermal energy would be greater for the higher temperature.

I hope that helps. Best wishes for success in your class.

## Static charges and slugs

January 14, 2019

### Question

Hello. I want to find a combination of materials that will hold a static charge for as long as possible to repel slugs and snails from a planter.
I have bought a copper braid copper adhesive strip for the purpose, but I want to find out that if I was to line the inside circumference of the planter with 15mm copper pipe and induced a very low current,(not enough to kill them, but enough to see them off)how long would either the static charge last as environmental conditions would influence this as well as a battery charge. Any help would be appreciated, thanks

mark - UK (28913)

One of the methods to get rid of with static electricity is explained in: How do I Get Rid of Slugs and Snails in my Garden? listed under "Give them a shock".

The method states that since slugs leave a slime trail, by using copper tape the slugs will get small electric shocks from the static electricity caused by the copper-slime combination.

The electric charge would only hold while the slug is moving along the copper tape.

I hope that helps. Best wishes in getting rid of those pests.

## Misc

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