Physics Feedback
by Ron Kurtus
Readers have sent in a total of 880 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 |
| 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 |
| Distance sound travels | Sound Echoes | Bangladesh |
| Relationship between magnetic force and electricity | Electromagnetism | Nigeria |
| Instantaneous velocity and acceleration | Acceleration | India |
| Difference between vaporization and sublimation | Dry Ice | Kenya |
| Magnetic alignment | Magnetism | Ghana |
| Reducing permanent magnetism | Basics of Magnetism | New Zealand |
Kinetic Theory of Matter
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)
Answer
The Kinetic Theory of Matter states that matter is composed of a large number of small particles—individual atoms or molecules—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.
General
Branches of Physics
July 8, 2019
Question
What are the branches of Physics?
kevin - Kenya (29096)
Answer
Branches of Physics include:
- Classical physics
- Modern physics
- Nuclear physics
- Atomic physics
- Geophysics
- Biophysics
- Mechanics
- Acoustics
- Optics
- Thermodynamics
- Astrophysics
Convention for Direction in Gravity Equations
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)
Answer
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
Matter
What are quarks?
April 30, 2019
Question
Physics
What are the quarks ,and did it found before or after the (the Big Bang Theory).
Abdelgadir - Sudan (29021)
Answer
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.
General
Properties of good insulators
February 1, 2019
Question
what are some good properties of good insulators.
ruben - USA (28933)
Answer
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.
Visible Light
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)
Answer
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.
Derivation of Velocity-Time Gravity Equations
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
Can you please help understand how this equation has come
Srinivasan - India (28924)
Answer
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.
Thermal Potential Energy
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)
Answer
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 Electricity Shocks
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)
Answer
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.
Sound Echoes
Distance sound travels
November 20, 2018
Question
the sound of echoes is heard after 0.12 sec.what is the distance between the source and the reflecting surface when temp of the place is 30 degree Celsius
nasiba - Bangladesh (28840)
Answer
The velocity of sound in air at 30 degree C is: 349.4 m/s. (see Speed of Sound in a Gas).
The distance traveled in 0.12 sec is then 41.9 m. Thus, the distance between the source and reflecting surface is 1/2 of that or about 21 meters.
Electromagnetism
Relationship between magnetic force and electricity
October 23, 2018
Question
my question is, what is the relationship between magnetic force and electricity?
Abdulrahman - Nigeria (28756)
Answer
See Moving Electrical Charges Create Magnetic Field. It shows that when electrical charges move, they create a magnetic force field. Likewise, a magnetic force can create electricity. See Basics of Electromagnetism.
Acceleration
Instantaneous velocity and acceleration
October 15, 2018
Question
what is the difference between instantaneous acceleration and instantaneous velocity?
sona mariam - India (28749)
Answer
Instantaneous velocity is the velocity of an object in motion at a specific point in time, as opposed to the average velocity.
Average acceleration is the change in velocity over a period of time. Instantaneous acceleration is the acceleration of an object in motion at a specific point in time.
Dry Ice
Difference between vaporization and sublimation
October 11, 2018
Question
Differentiate between vaporization and sublimation
Kevin - Kenya (28745)
Answer
Vaporization is the process that occurs when a chemical or element is converted from a liquid or a solid to a gas.
When a liquid is converted to a gas, the process is called evaporation or boiling.
When a solid is converted to a gas, the process is called sublimation. This is what happens with dry ice (frozen carbon monoxide gas).
Magnetism
Magnetic alignment
October 8, 2018
Question
what is in the iron that makes magnetic substance attracted by it
obed - Ghana (28741)
Answer
It is the alignment of the electrons. See: Factors Determining Magnetic Properties.
Basics of Magnetism
Reducing permanent magnetism
October 6, 2018
Question
If you have a weak permanent magnet and wind a multi turn coil around it and then pass an electrical current through the coil, can you negate the magnet strength of the magnet?
Will a specific current be required to reduce the magnet strength to exactly zero?
Charlie - New Zealand (28738)
Answer
You can demagnetize a permanent magnet by hitting it with a hammer or heating it to a sufficient temperature. Both cases disrupt the alignment of the atoms.
The problem with using a coil is that the atoms can be realigned into a different direction, thus still maintaining the magnetism. The only way to reduce the strength of the magnet is to get some or all of the atoms in random orientation.
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