Concept Definition and 1000 Threads

of a countable collection of open intervals. I'm having a hard time seeing how this could be true. For instance, take the open set (0, 10). I'm having a hard time seeing how one could make this into a union of countable open intervals. For instance, (0,1) U (1, 10) or (0, 3) U (3, 6) U (6, 10)...

Hey guys, I have been thinking of creating a flashlight that is powered by piezoelectric (pressure) energy. I have watched several videos so far and I noticed that in order to actually generate electricity, one would have to constantly tap it rapidly in order to power an LED light. However, I...

Suppose we have a wedge with angle θ on which there is a block. We are pushing the wedge with the least force required to keep the block stationary. If the acceleration of wedge is A then the acceleration of the block along the inclined plane will be gsinθ+Acosθ=0. That means A is negative. How...

I've heard light compared to vibrations under the earth. The "waves" between the tectonic plates are simply a 'state', or 'action', i.e, the action of millions of atoms "bumping" into each other with their opposite charges (all the valence electrons repel other electrons). From my...

Hello, I’m a sci-fi writer and I wish to gage the believability of (or lack of) the following which I’m using in a story. Concerning the extensions to cosmology and quantum physics, one of the cornerstones of my book’s sci-fi universe stems from a strange and intriguing fact that I’ve...

Greetings. I am in part-time studies for my undergraduate I am taking physics for the first time. I am completely overwhelmed and am having a hard time of finding answers to the textbook questions in the textbook itself. The current question I am stumped in is: Suppose zinc is illuminated...

I want to know whether I can use a point where all charge of a body can be assumed to be concentrated. Obviously such a point exists. I want to know whether it'll be the same point as centre of mass [as both are scalars and their integration SHOULD yield the same result] For example, if a...

Hi all; Look at the attached part from Van Dalen's Logic and structure. What is he doing exactly? In axiomatizing 'Identity' as he does, what is gained rather than what we had before (i.e., looking at 'Identity' as a binary predicate)?! Even in the axioms, he is again using a symbol in the...

Need to ask a question. Weightlessness occurs when the net force acting on a body is zero.For example,consider a person in orbit.The centripetal force provided by gravity of the Earth is balanced by the outward centrifugal force therefore the net force on the person becomes zero and he becomes...

This may sound really silly but yeah, a plane mirror, and a white sheet of paper, both reflect all the wavelengths of light incident on them. So Instead of a plane mirror, if I use a white sheet of paper, Why don't I see a reflection of myself? I have studied ray diagrams, and i know how an...

The term "mass" is the source of many conflicting opinions among the authors writing on relativity theory. Different authors denote by this term different concepts. Quite often even the same author denotes by mass different concepts in his different writings. For instance when introducing...

Hello everybody, this is slightly embarrassing (for a physics student), but I realized in the last couple of days that I am somewhat confused with the concept of "pressure". Pressure is defined in "school-level" as "force per area". So if I have a plate of 2m^2 on which a downwards force...

Hello everyone. I'm very...very new to electronics, and am looking to get into the 'maker' world, of building small electronics, and projects. One concept though that has bothered me is the concept of grounding. Now I've come to understand that ground wires in homes have that bottom plug...

let Rg be the resistance of the galavanometer. A formula in my book states that V=Ig(Rg+R) my doubt is: here Ig(Rg+R) is the potential drop across the two resistors of the voltmeter. But how can this include the potential drop by the circuit element across which the voltmeter is connected.

Hi, Is there a concept map that actually shows all the concepts of math, and how they relate to each other? Kind like this one but more complete. I alreaady searched the web and didn't find anything, that's why I'm here so, Please Help. Thanks.

Hi, I'm new to physics and have some trouble understanding the concept of Kinetic Energy. It's not that I don't understand the definition given to me, I do, but I don't feel the intuition behind the concept. Here's what I understood of the concept : Kinetic energy comes from moving objects (If...

Hello, I was wondering if there is a conceptual explanation for when current leads voltage or vice versa for capacitors or inductors with AC voltages, or is it just the way the math pans out?

Homework Statement A student throws a set of keys vertically upward to her sorority sister in a window 4m above. The keys are caught 1.5s later by the sister's outstretched hands. (a) With what initial velocity were the keys thrown? (b) What was the velocity of the keys just before they were...

Homework Statement A block slides from rest down a frictionless ramp which is 4 m long and has a 30 degree angle with respect to the ground. After reaching the bottom of the ramp it slides on a frictionless surface and compresses a spring a distance of 12cm (.12m) before coming to rest...

I was just thinking about absolute zero temprature roughly -250 c degress Lets say an object has a room temprature of 20 degrees celcius Doesnt it mean i has a lot of thermal emegy So i used the equation H= Cp x M x ΔT H = Heat energy (in Joules) m = mass (in kilograms) delta T =...

Homework Statement Homework Equations The Attempt at a Solution Well since spring is in SHM, only conservative forces are at play here. So using conservation of energy, the kinetic energy would be the change in potential energy. Which I have set up as KE = 1/2k(A^2)2 -...

I have just a few more questions regarding index of refractions and reflections... 8. A fly is 10 cm above the surface of a pond. How high above the water does the fly appear to a fish directly below (nair = 1, nwater = 1.333)? (A) 10 cm (B) 7.5 cm (C) 13.3 cm (D) 12.5 cm (E) fish cannot see...

7. The figure shows the path of a portion of a ray of light as it passes through three different materials. What can be concluded concerning the refractive indices of these three materials. (A) n1 < n2 < n3 (B) n1 > n2 > n3 (C) n3 < n1 < n2 (D) n2 = n1 > n3 (E) n1 = n2 < n3 The...

Hi friends, I have an idea what a markov chain is. But when it comes to HMM (hidden markov model) I have a doubt regarding emission matrix. What is emission matrix? I have an idea of transition matrix , current states etc. when coming to simulation (using Matlab) I don't have a...

Hello, this is not a homework assignment. I am referencing an old assignment from a few semesters ago. I am curious if I can use the basic:dB = mu/4pi dq * v X r /r^2; where dq = sigma*da=sigma*L*dx; instead of just using Amp's Law. this stuff was fun...dunno if i was at all correct...

I have read about polarisation... just a little ques about concept... in case of circular polarisation there is 90 degree phase difference between the two v and h, e field component... right... and in case of linear polarisation the e field is restricted to oscillate in only one plane...

Hi all - thank you for this forum - it's proving very helpful: Am I correct in thinking that if we measure a period of time that light travels, that in the case of red vs blue light: 1) Both will travel at the same speed in a vacuum? 2) More blue photons will arrive than red (given...

Homework Statement Homework Equations The Attempt at a Solution How are their angular velocities the same? I thought Angular velocity = v/r where v = velocity and r = radius. In this case isn't the radius of big ben much larger and therefore have a much smaller angular velocity?

I'm not sure I know all that I should to understand it. I'm posting to try and determine if I do. Knowing what I know, however, it seems unnecessarily confusing. Almost all students I talk to agree. Why not just call it a particle on a line segment? Or just moving in one dimension?

Hi, I am revising my intro to nuclear physics class and was wondering why is parity so important ? I mean OK, I get it, physicists are crazy about symmetries, but I do not understand what does it physically mean... I was wondering if someone could possibly talk me through its importance and...

Here is a text from my Physics Book : The net external torque on the object about any axis must be zero for it to be in rotational equilibrium. I divide the torques into two categories, anticlockwise and clockwise. (This approach works fine for 2-D objects but will it work for 3-D objects...

The physical pendulum is an object suspended from some point a distance d from its center of mass. If its moment of inertia about the center of mass is given by: I= Icm + Md2 where d is the distance from the pivot to the center of mass of the pendulum. Consider that some odd-shaped physical...

So I feel as though I have the correct solution, but am not positive. My problem is as follows: A block of mass M is at rest with respect to a surface which oscillates horizontally with sinusoidal motion described by the equation x(t)=Asin(ωt). Find an expression for the minimum value of the...

Can work also be the transformation of energy? For instance, an object in free fall goes from an initial height (that has potential energy) to a final height where there is kinetic energy. If energy is conserved then how is work being done?

Hi, I've been listening to the podcast "Neuroscientists Talk Shop" and heard some participants repeatedly refer to something called "cosine tuning" in relation to predicting the efferent reactions to certain clusters of neurons (e.g. a simian moving in a certain way). [sorry if that's...

Generally the concept of dipole moment is used in neutral system, ie the total positive charge equals to the total negtive charge. Could the concept and also the calculation be used in charged system? For example, NaOH, (Na+)(O-2)(H+), we can calculate its dipole moment. Could I calculate...

Why is it that (x + y)!=(x + y)(x + y - 1)(x + y - 2)...(x + 1)x! Where did the last "x!" come from? Thanks

Thanks! Please answer, Mr. Donis! Also, if someone could simplify the difference between a reference frame (used today) and a reference body (used in Einstein's book) please do so!

hi.. I have been struggling, since a long time, to understand how is the diffraction pattern obtained by a slit of width of the order of the wavelength of light used is obtained, but found no answers! As per the idea of wave theory (and Fermat's principle) it is the wave nature (specifically...

A "concept" problem in "overpressure" Here's the kind of physics problem that really drives me crazy: The overpressure in a tire is 2.4 atm on a day when the atmospheric pressure is .95 atm. So, on a day when the atmospheric pressure reads 1.01 atm, what will the overpressure be ...

I am very confused about the physical meaning of the concept "flux" I am really trying to understand what it means, what unit it has, but I keep reading contradicting definitions. So, on the one hand, I read that "...flux is defined as the rate of flow of a property per unit area, which has...

I have a problem involving the rotational version of Newton's Second Law. A spool is resting on a tabletop. A wire is wound around it counterclockwise and the free end of the wire goes over a pulley (located to the right of the spool) at the end of the table and attaches to a hanging mass. What...

I'm having some very basic conceptual problems about tension. If you have a pulley where two masses are hanging on opposite ends of an ideal string, why is the upwards force that the one mass experiences the same as the upwards force that the other experiences? People have tried to explain...

In a two-dimensional statics problem involving finding a moment about a point, I don't understand how the result is either in the positive/negative z direction. I realize moments are found by the cross product, and the cross product requires the answer to be perpendicular to the plane that...

The concept of a "rate" Here's another question from good ol square :| I was hoping to get some clarification about the concept of a rate of two quantities, with different units, like speed \frac{a-units}{b-units}. How does the expression for division \frac{a-units}{b-units} arise from the...

Homework Statement Are the momentum eigenfunctions also eigenfunctions of e free particle energy. Operator? Are momentum eigenfunctions also eigenfunctions of the harmonic oscillator energy operator? An misplayed system evolves with time according to the shrodinger equation with potential...

Hello, . . I have this concept sketch, of a new configuration from what I have been seeing in,. "wave energy", (in this case tide flow force energy), . . I believe that generally speaking, as a concept, there seems to be advantages. Although this is just the water wheel without turbine in...

can anyone tell me who gave the concept of moment.

The most common definition of mass, at least in the Newtonian context, is in terms of a measure of inertia: The mass of an object is a measure of, and gives rise to, its resistance to changes in motion. F=MA presumably quantifies this idea of inertial mass. I'm wondering whether any...

I have problems with a(ii). (please view the first image.) Now I have found that w = (13-8e)u/7 and v = (20e+13)u/7 What I did is like this: (Using NEL) v = 4ue Where the LHS is actually v-0 because I assume Q = 0. (20e+13)u/7 = 4ue e = 33/28 >1 ∴ e cannot exist. 1. Is...