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Jan16-12 Greg Bernhardt
Contributed by ZapperZ and arildno. This question has popped up many times. So here is an attempt to address it. ...
May25-09 10:31 AM
ZapperZ
0 27,269
Do Photons Move Slower in a Solid Medium? Contributed by ZapperZ. Edited and corrected by Gokul43201 and inha ...
Feb2-06 07:47 PM
ZapperZ
0 12,326
WHY DONíT ELECTRONS CRASH INTO THE NUCLEUS IN ATOMS? Contributed by Marlon and edited by ZapperZ If one...
Dec20-05 01:14 PM
ZapperZ
0 10,755
This forum contains simple responses to the most frequently-asked questions in the Physics sub-forums. It is a...
Dec20-05 01:13 PM
ZapperZ
0 9,365
IS LIGHT A WAVE OR A PARTICLE? Contributed by Marlon and ZapperZ. In our ordinary world, “wave” and “particle”...
Dec28-05 01:43 PM
ZapperZ
0 8,587
Contributed by vanesch. The short answer is: no, there's no violation. The longer answer can be this: Given the...
May11-06 10:35 AM
ZapperZ
0 7,855
heat Sticky Thread Pinned: What is Heat?
Written by Hootenanny. Edited by berkeman and Kurdt. Feel free to contact me with any questions, comments or...
Feb3-08 12:04 PM
Hootenanny
0 7,789
Definition/Summary Work is a measure of change of energy. The net work done equals the change in Kinetic Energy...
Jul24-14 11:39 AM
Greg Bernhardt
0 707
Author: ZapperZ Originally posted on Jan25-12 "... then you haven't understood it." We all have heard...
Aug12-14 11:12 PM
Simon Bridge
1 312
Author: ZapperZ Originally posted on Apr24-13 We periodically get questions on PF about people wanting to know of...
Aug12-14 02:02 PM
Greg Bernhardt
0 297
Definition/Summary Stress is force per area, and is a tensor. It is measured in pascals (Pa), with dimensions of...
Jul24-14 11:29 AM
Greg Bernhardt
0 275
Definition/Summary A Slater determinant is a representation of a many-particle wave function for a system of...
Jul24-14 11:26 AM
Greg Bernhardt
0 258
Definition/Summary Voltage is electric potential difference, which is potential energy difference per charge: V\ =\...
Jul24-14 11:36 AM
Greg Bernhardt
0 257
Definition/Summary One of the most asked questions is concerning how to derive the Heisenberg Uncertainty Relation....
Jul24-14 11:34 AM
Greg Bernhardt
0 253
Definition/Summary The double-slit (or 'two-slit') experiment clearly demonstrates that individual particles...
Jul24-14 11:38 AM
Greg Bernhardt
0 252
Definition/Summary This is a derivation of the Uncertainty Principle based on the properties of non-commuting...
Jul24-14 11:33 AM
Greg Bernhardt
0 249
Definition/Summary Virtual particles are a mathematical device used in perturbation expansions of the S-operator...
Jul24-14 11:35 AM
Greg Bernhardt
0 249
Definition/Summary Vectors (such as velocity or force or momentum) obey the Vector Law of Addition. That means...
Jul24-14 11:35 AM
Greg Bernhardt
0 242
Definition/Summary Susceptibility is a property of material. In a vacuum it is zero. Susceptibility is an...
Jul24-14 11:29 AM
Greg Bernhardt
0 240
Definition/Summary Torque is the moment of a force about a point. Torque is a vector (strictly, a pseudovector,...
Jul24-14 11:32 AM
Greg Bernhardt
0 237
Definition/Summary A wave function is a mathematical function that describes a physical system in quantum...
Jul24-14 11:37 AM
Greg Bernhardt
0 237
Definition/Summary Take the case of a string with it's one end tied to a wall. The other end is held by you. It...
Jul24-14 11:38 AM
Greg Bernhardt
0 237
Definition/Summary Snell's Law relates the angles of incidence and refraction, for a light ray that passes between...
Jul24-14 11:27 AM
Greg Bernhardt
0 226
Definition/Summary A spring is a mechanical device that produces a restoring force when stretched or compressed....
Jul24-14 11:28 AM
Greg Bernhardt
0 226
Definition/Summary Time-order means in order of time. A sequence or product is in time-order if "earlier" items are...
Jul24-14 11:31 AM
Greg Bernhardt
0 226
Definition/Summary Pressure is normal force per area, or work done per volume, or mechanical energy per volume...
Jul24-14 11:11 AM
Greg Bernhardt
0 216
Definition/Summary For a given material, the resistance of a length of the material is a constant times its length,...
Jul24-14 11:17 AM
Greg Bernhardt
0 215
Definition/Summary Nonlinear optical processes that occur due to the presence of a second-order nonlinear...
Jul24-14 10:58 AM
Greg Bernhardt
0 212
Definition/Summary Permittivity, \varepsilon, of a material is its ability to separate charge when a voltage...
Jul24-14 11:05 AM
Greg Bernhardt
0 212
Definition/Summary Poincare's integral invariant is the most fundamental invariant in Hamiltonian Dynamics. For any...
Jul24-14 11:07 AM
Greg Bernhardt
0 212
Definition/Summary Net force = rate of change of momentum (= mass times acceleration of the centre of mass, if the...
Jul24-14 10:56 AM
Greg Bernhardt
0 210
Definition/Summary There are three masses of neutrino (they are unknown, but the differences of their squares is...
Jul24-14 10:55 AM
Greg Bernhardt
0 209
Definition/Summary Between two bodies in contact, there is a pair of Reaction Forces. They are always equal but...
Jul24-14 11:16 AM
Greg Bernhardt
0 207
Definition/Summary Light propagating through a vacuum will obey the principle of superposition, however this is not...
Jul24-14 10:57 AM
Greg Bernhardt
0 206
Definition/Summary An object (typically a "mass on a spring") which has a position (or the appropriate...
Jul24-14 11:24 AM
Greg Bernhardt
0 198
Definition/Summary Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting...
Jul24-14 11:14 AM
Greg Bernhardt
0 197
Definition/Summary The second law has various forms. I shall give these here then show how they are logically...
Jul24-14 11:23 AM
Greg Bernhardt
0 195
Definition/Summary "Rolling" means moving along a surface without sliding. The (instantaneous) point of contact...
Jul24-14 11:19 AM
Greg Bernhardt
0 194
Definition/Summary Often in physics we need to consider frames of reference that are non-inertial (the Earth...
Jul24-14 11:20 AM
Greg Bernhardt
0 194
Definition/Summary Moments of area are properties of rigid bodies, they depend only on shape and not on density,...
Jul24-14 10:50 AM
Greg Bernhardt
0 193
Definition/Summary Momentum is mass times velocity. It is a vector. \mathbf{p} = m\mathbf{v} Angular momentum...
Jul24-14 10:54 AM
Greg Bernhardt
0 192
Definition/Summary This entry describes diffraction of a wave when it passes through a single narrow slit. ...
Jul24-14 11:24 AM
Greg Bernhardt
0 192
Definition/Summary This is the quantum-mechanical version of the classical harmonic oscillator. Like the classical...
Jul24-14 11:13 AM
Greg Bernhardt
0 187
Definition/Summary Why is a sound wave reflected at the open end of a pipe? Why doesn't it just "escape"? ...
Jul24-14 11:04 AM
Greg Bernhardt
0 185
Definition/Summary In the Hamiltonian formulation of classical mechanics, equations of motion can be expressed very...
Jul24-14 11:08 AM
Greg Bernhardt
0 185
Definition/Summary Potential energy is simply another name for (minus) the work done by a conservative force. ...
Jul24-14 11:09 AM
Greg Bernhardt
0 185
Definition/Summary The moment of a vector is the cross-product of the position vector with that vector (e.g., a...
Jul24-14 10:53 AM
Greg Bernhardt
0 183

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