Concept Definition and 1000 Threads

After a fair bit of time in Physics, I have started to, intuitively, see the big picture. That is, in the area of electricity, mechanics and thermodynamics, there are certain vital concepts that are central such as work and energy. Semantics are involved but they essentially refer to the same...

What are possible explanations as to why variation persists in the natural world despite the effects of genetic drift and directional selection?

it is involved the concept of inertia ?? when a plane is flying on the sky , sometimes it will remain the constant velocity,right?and the force is balanced therefore , it does not have any force? why the plane can keep moving at the constant velocity ? due to inertia ? :confused::confused:

Let's use the material brass as an example. My problem is that I have no understanding of the concept of "phases". In the phase diagram for brass, we have α, β, γ, δ, ε, and η phases as well as the liquid phase (L). My question is, how do I interpret these phases? What is the difference...

Homework Statement So if light travels from vacuum to oil to water (1 -> 1.4 -> 1.33) how do you know if there is a constructive or destructive interference? Homework Equations The Attempt at a Solution I know that when it goes from air to the oil there is a phase shift of 1/2...

I am having problems getting any intuitive idea on the concept of Action (as in the Principle of the Least...) when the Lagrangian is T-V. Every site I visit starts with the mathematical formulation, which is fine, and I understand that not every physical concept comes with an intuitive idea...

A box containing a pebble is attached to an ideal horizontal spring and is oscillating on a friction-free air table. When the box has reached its maximum distance from the equilibrium point, the pebble is suddenly lifted out vertically without disturbing the box. Will the following...

Hi I am kind of Confused about an example in work done: It says that a man applies 250 N parallel to the slope to push a box up a slope for 3 m, Now I know that the formula for work done if Force by Perpendicular distance which is 250 x 3 = 750 (which is the correct answer in my book). The...

Im working on designing a high speed flywheel as part of a project. The main issue is the centrifugal forces acting on the flywheel to tear it apart. If i was to construct a flywheel using interference fit tubing which is put together using thermal expansion of the outer tubes so that they are...

What is the concept behind Diffraction, "n", Finding Dark/Bright Spots I used the following youtube video to help me learn about the concept of diffraction but still could not make sense of my lecture notes: (All 4 parts) SINGLE SLIT DIFFRACTION In order to find the minima the following...

Will someone please remind me why int from 0 to 1 of 5 equals 5, when the sum of the values 5 at, say 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 is > 5? I lost this fundamental understanding today and want to gain it back. Thank you

Hi all, Well, I'll try to explain my doubt with an example. The idea of force formalizes what we intuitively think as a push or a pull, torque formalizes what we think as a turn, linear and angular momentum respectively capture the idea of "how much something is moving" and "how much...

(Warning, a dumb question incoming :smile:) Just got curious while reading an article on photoelectric effect. Why doesn't the mass of electrons increase(because electrons already revolve at the speed of light) when it absorbs photons instead of increasing radius of orbit? (Sorry for...

A couple questions about a "hot room" concept. I had an idea that I may try to implement should I ever get around to building my dream house. I think of it as a "hot room". The idea is that there is a utility room which is positioned to receive most of the wast heat generated by household...

Hello friend... I have confusion in understanding the concept of viscosity. Please help me. Viscosity is the property of the fluid which offers resistance to the movement of one layer of fluid over another adjacent layer of the fluid. Here both top and adjacent layer causes shear stress on each...

Im designing a flywheel based kinetic energy recovery system for a car. The flywheel needs to have a very high angular velocity to store enough energy. At high angular velocities centrifugal forces will act to pull the flywheel apart, away from the centre of rotation. If i could somehow, maybe...

Homework Statement Hello PF :smile: i am stuck with a concept of weighted resistor D/A converter. For a 4-bit resistive ladder, VA={V0/R0+V1/(R0/2)+V2/(R0/4)+V3/(R0/8)}/{1/R0+1/(R0/2)+1/(R0/4)+1/(R0/8)} I want to find out how the equation is derived but have no clue. Thanks.

Hi, I am new to control system and coding.my problem is suppose we have a steering value and know we need to turn the vehile. I facing difficulty in understanding some equations. phi=T*st. %here st. is steering value and 'T' is some constant , but I am facing difficulty to understand...

If I comb my hair with a rubber comb, the comb can be used to pick up small bits of paper on a desk. This says that there is a force between the comb and the paper bits. If the paper bits are uncharged why are they attracted? You can pick up paper bits by pulling a piece of scotch tape frm a...

Can "relativistic mass" be a useful concept Many basic texts on relativity refer to the mass variation equation: m= gamma mo [gamma = Lorentz factor, mo= invariant(rest) mass] It seems that there are some good reasons including,for example, problems with definitions of...

concept problem, we can determine the possible value of Lx in hydrogen atom? The book of introduction to quantum mechanics told me that The value of Lx can not be determined. I know the concept behind this statement However, when I am practicing, I see one of my question that requires me the...

Homework Statement The Concept of the reduced mass was introduced Homework Equations What is the application for the μ,which we have to learn, in questions like in shm or collision So i was just wondering if you could show me some examples where in the concept of reduced mass has...

Homework Statement Some gas at 300K is enclosed in a container. Now the container is placed on a fast moving train. While the train is in motion what happens to the temperature of the gas? Homework Equations KE(total) = (3/2)(N_A)nkT KE(avg) = 3/2kT The Attempt at a Solution My...

Homework Statement I just have a general question regarding scales and forces. I came across a question that when a boy jumps on his scale, the weight shown is actually greater than his actual weight. I have a hard time picturing this because when he jumps, he isn't actually on the scale...

Hello. In my textbook by Jose Saletan called Classical Dynamics: A Contemporary Approach the author talks about TQ, the domain of the Lagrangian. He states that the space tangent to a point on the configuration manifold is in the tangent bundle, and that the entire tangent bundle can be thought...

I am having a bit of trouble understanding something in my textbook and was wondering if you guys could help clarify. We just learned Faraday's Law that a time variant magnetic field will enduce an emf in a coil. What my textbook says is that " The electric field in the loop is NOT...

Homework Statement 1.Where would you place an object to obtain an image as far away from the lens as possible? 2. Suppose you have an image focused on a slide screen. You moved the image towards the lens. Which way would you move the lens to keep the image in focus? Explain Homework...

Homework Statement Hello PF:smile:, i have a serious problem on circular motion. My textbook says that angular velocity =linear velocity /radius While the my another book specialized in physics says that angular velocity=vertical component of velocity/radius. I am not understanding if both...

Hi all I am trying to understand the concept of 3 phase wound rotor induction motor. I understand why when you feed in 3 phase current to the stators that are separate spatially 120 degree will get you a rotating magnetic field. However, I am having much trouble in understanding the...

In SR there is a whole family of so called inertial observers that are defined as those observers that move at relative constant speed with respect to one another, whose descriptions of nature are all equivalent and whose spacetime coordinate are related by Lorentz transformations i.e. those...

Maybe I need to take a little break from my studies but I'm not getting this at all. At the risk of looking really dumb, here's what I need help with; Imagine that you are living in a rotating space habitat. The habitat has a diameter and a rotational speed such that at the outer edge you...

Is There any impact/will there be any: of the concept of Einstein’s New Ether in science today? I red that even though Einstein rejected aether in his relativity theory he introduced it back in 1920 to explain his theory of gravity. I don't know if he ever published it as a theory or it has...

Homework Statement See the picture attached please. I need help understanding the concept of why work is = 0. I don't understand it's explanation. Please bare with me for the silly questions. Homework Equations W=Kf-Ki W=Fdcosθ The Attempt at a Solution I can't understand...

I have looked at this forum for over a year. One thing that has always confused me is spatial direction in space. Thinking in terms of the balloon model: what represents the part in front/beyond if we are on the edge looking out. If we are looking out why can't we "turn around" and see the...

I just couldn't grasp the idea what are differentials,intuition behind them,applications of differentials? can anyone thoroughly tell me about it please? and why sometimes dy/dx is taken as a fraction?

Hi, I have been pondering a special relativity question about the concept of simultaneity when moving at speed of light. Say for instance I took a round trip to Alpha Centauri 4 light years away, traveling at the speed of light both out and home (using negligible time to turn around). Then...

Hi, This is a little different from most questions in that it's not something I want to solve, but rather hoping I could get a little clearer explanation on what mapping is and why/when we use it? I'm soon to go over conformal maps, but I don't think i understand anything to do with mapping as...

Homework Statement [EDIT] Cleaned up the problem. A tread wheel crane is an ancient device used to lift heavy objects. It consists of a large circle (like a hamster wheel) for a person to walk inside. The large circle connects to the middle where there is a small circle that is attached a rope...

Homework Statement Three different cars (a red one, a blue one and a green one) are driving with an identical velocity. Suddenly they all slam on the brakes and skid to a stop. The red car is the most massive and the blue one is the least massive. Each of the three cars has identical tires...

From what I understand, the speed of any object in the universe can only be measured relative to another object in the universe. . . . If this is the case then how can we say time slows down for an object traveling at super high speed. Who is to say which object is moving at super high speed...

Imagine mirror image of a cell - built from a scratch using mirror images (enantiomers) of molecules of the original cell. It should work as standard one, but use e.g. L-sugars instead of our D-sugars: article. Some possible applications: - doubling the space of possible enzymes we could...

I need help understanding why in problems tension is modeled as T-mg = ma. I understand there are different variations, but the main concept is what I need help with. For example: If i have 2 masses hanging off a pulley (m1=5kg & m2=10kg) then m1 has a downward force of 49N down. The...

Describe a situation in which the net external force is not zero, but its speed remains constant. I don't know if this situation is possible to explain.

I can not find a formula to calculate the following question, any help would be appreciated, ty AlephZero for helping me clarify my question. An example in my problem set (homework help) An oak rod is hung from a rigid support. The rod has a diameter = 13 mm, length = 7 m, and a catch plate...

is black hole a theoretical concept or a natural phenomenon?

When a Rigid body is said to be in planar motion, if all all the particles in the Rigid body moves in same plane and these planes are parallel to each other. I think i misunderstood this definition especially the particles moves in same plane and these planes are parallel to each other...

Hi,I know,that my question is trivially and frequently asked question,but thread,where I have colud post was closed.So I made new one. I can report,what I know. Equation is something what equals each other.One statement to another.So 10=2x is equation. Function is concept which gives us...

Hi all, I am trying to wrap my head around this and for some reason I am blocked. I have taken Solid mechanics and strength of materials and am always used to calculating strain as ε=ΔL/L. I might be missing something easy as it has been a year since the class but in my Manufacturing...

Hi to everyone, I study industrial design at faculty of mechanical engineering and It is time to start thinking about the theme of my thesis. So I have seen this, and was terribly dissapointed, when I found out it's just CGI. We've all seen quantum levitation videos before, so this thing is...

Question: Explain why you cannot solve the ordinary equation? x^2y'' + xy' + (x^2-1)y = 0 My attempt: I don't need to solve it, but just simply state why I can't with just differential equations So my answer is, This differential equation does have a solution, it's just not expressable in...