Rest Definition and 558 Threads

Einstein's theory of relativity is based on the fact that all motion is relative, which precludes the existence of a universally defined state of rest (priviledged reference frame). Einstein also recognises the existence of rest mass. If an object were at its rest mass, wouldn't it be perfectly...

I wanted to discuss Lorentzian length contraction (and time dilation, for that matter). Books on the subject do a fine job describing it but I've generally found that they lack an adequate explanation of it. What follows is my personal explanation. Special Relativity, in my opinion, is best...

Does proton diameter increase with the addition of energy, such as thermal energy? I guess this is also to ask if a particle's rest mass can increase. And, if a proton can gain rest mass, does the diameter correlate with it?

Let a clock A be at rest in an inertial frame and let a clock B rotate around it with constant velocity and constant distance from A. Let v be the velocity of B relative to the inertial frame. Both clocks count how long it takes for B to rotate once. According to clock A, the time it takes is...

In an earlier thread, I asserted that a rod has one true length, its rest length. If so, then the shorter coordinate length which is measured in some other frame must be somehow untrue. In this thread I argue that the coordinate length is a distorted view of the true length. In the graphic...

I've read that in relativity the concept of the rest frame of a photon doesn't make sense. Why is that? A rest frame of some object is a reference frame in which the object's velocity is zero. One of the key axioms of special relativity is that light moves at c in all reference frames. The rest...

I have been trying to calculate how far a golf ball will travel on a level green given the following variables: The initial velocity of the ball is 1.49 m/s The coefficient of friction between the ball and the green is .0409 The mass of the ball is 0.046kg The diameter of the ball is 42.6mm...

I haven't used the template because I just need some reassurance on understanding a topic, not help with a question! When two particles annihilate (e.g. proton and antiproton), the resulting radiation will have a minimum energy of the sum of the rest mass energies of the two particles, right...

Okay, so I know that E=MC2, is an equation in regards to an object at rest. But I recently came across another formula: m² = E² - p²; in the description, it stated, that it was basically E=MC2, in regards to an object in motion. Is this information valid?

EDIT: Problem solved, the mistake was in the statement that the point of contact traces out an arc of length \theta r on the hemisphere. This statement neglects the change in orientation of the sphere relative to the hemisphere. An object with cylindrical symmetry (Full/hollow sphere, cylinder...

Rest mass ? What on Earth ?! I have a data table given to me by my examining body and it lists the REST mass of a proton and the REST mass of an electron along with their values. My question is why do they specify the REST mass ? Does the mass of either sub atomic particles change when they...

Homework Statement There is a solenoid with a magnetic field of a constant magnitude B. In this solenoid is a charged particle, initially at rest, at a certain distance r from the axis of the solenoid. After a certain amount of time, the magnetic field is instantaneously flipped in direction...

Homework Statement Determine the emf induced in the square loop in the figure if the loop stays at rest and the current in the straight wire is given by I(t) = (15.0 A)sin(2500t) where t is in seconds. The distance a is 12.0 cm, and b is 15.0 cm. Homework Equations In the question...

This is not a question from homework, but one about which I was curious. If a ball starts at rest at the top of frictionless plane, would it roll or slide down the incline? The thing that confuses me is that it seems like it should just slide, since there is no friction and thus nothing to...

Homework Statement A pitcher can throw a baseball at 44 m/s. what is the ratio of kinetic energy to the rest energy E=mc^2. (can you use k=1/2mv^2 ?) Homework Equations rest energy=mc^2 K=gamma*mc^2 - mc^2 k=1/2mv^2 The Attempt at a Solution I am just not sure how to go about...

A 253.5 kg cannon rests on a frozen pond. The cannon is loaded with a 6.8 kg cannon ball and is fired horizontally. If the cannon recoils to the right with a velocity of 6.9 m/sec , then what is the velocity (in m/s) of the cannonball just after it leaves the cannon? Also would like a hint...

Homework Statement In an experiment, a ball was released from rest at the top of a slope and rolled a distance of 2.0 m down the slope in 8.0 s. Calculate (a) its average speed in this time (b) the speed after 8.0s from rest (c) the acceleration of the ball Basically, I got the...

Homework Statement Derive formula for elastic collisions in one dimension, unequal masses target at rest. i am having trouble acquiring the same formula that the book gives me, please tell me where my algebra is incorrect... i need to be able to derive these formulas properly because...

Homework Statement A 30.0 kg particle is initially at x=0 and has a velocity of 5.50 m/s. It encounters a position-dependent net force F(x) described by the graph shown (the graph continues indefinitely in the manner shown past x=20.0 m). Diagram...

I really don't quite understand the result of time dilation. Let's say that we have two identical twins A and B. Twin A is at rest and twin B is on a high speed rocket ship. Let's say that 10 years has passed in frame A. According to relativity, the twin in frame B is supposed to measure less...

Thermodynamics A rock of mass 0.19 kg falls from rest from a height of 15 m into a pail containing 0.37 kg of water. The rock and water have the same initial temperature. The specific heat capacity of the rock is 1885 J/(kg·C°). Ignore the heat absorbed by the pail itself, and determine the...

Homework Statement Find the least positive rest in division of 7^35 with 5 Homework Equations (7^35)/5 The Attempt at a Solution 7^35=378818692265664781682717625943 => 378818692265664781682717625943/5... Uhhhhh this is not the way I am supposed to take right? :cry:

hi, the following question is extremely important so please reply! in an atom, the energy levels of the electrons are negative and the velocity of the electron increases when the energy decreases. however, this cannot be the total energy(in relativity) because it does not includes the...

Consider the following situation. Two particles are initially separated by some distance and are then pulled further apart, thus increasing the potential energy of the system (due to the gravitational force of attraction between them). If I am correct in understanding special relativity, then...

Homework Statement The half life time of mesons \mu with velocity 0.95 c has been obtained experimentally as 6\times 10^{-6}s. Calculate the half life of those mesons in a system in which they are at rest. Note: It shouldn't be "half life" but something like "mean life" or something like...

Homework Statement A ball is dropped from a balloon going up at a speed of 7 m/s. If the balloon was at a height 60 m at the time of dropping the ball, how long will the ball take in reaching the ground ? Homework Equations u = –7 m/s, s = 60 m, a = g = 10 m/s^2 The Attempt at a...

Hi All, According to the basic notions of Relativity, in the reference frame, in which a certain body is at rest, we are allowed to measure the rest mass of this body. Nevertheless, we know from thermodynamics that at temperature T there is a certain amount of disordered microscopic movement...

Hi! Can someone tell me why Coulomb in his Wedge Theory of Earth Pessure didn't take into considertion Earth pressure at rest? He cosnidered only limit active and passive pressures, but why didn't he write anything about pressure at rest? I 've looked up some books, but there is only the...

Homework Statement A yoyo with a mass of m = 179 g is released from rest as shown in the figure. https://s6.lite.msu.edu/res/msu/nagytibo/Mechanics/Rotation/Graphics/001a.gif" The inner radius of the yoyo is r = 2.60 cm, and the outer radius is R = 3.60 cm, and the moment of inertia...

Homework Statement A skier starts from rest at the top of a hill that is inclined at 9.1° with the horizontal. The hillside is 250 m long, and the coefficient of friction between snow and skis is 0.0750. At the bottom of the hill, the snow is level and the coefficient of friction is unchanged...

I know this topic has been discussed before, but I wanted to get the opinions of those who have graduated outside the UK. (Also, there is usually some confusion over the UK and US educational systems, and this topic might clear it up.) In the UK it was usually the case where you went from a...

Sorry if this question seems more philosophical than scientific. It's my first post in this forum. I love learning about the way the universe works and I always have lots of questions :-) Alright, so to my point. It seems like the theory of relativity says that the faster you move (plus how...

Is rest mass just an illusion? In Proton, for example, most of the rest mass is relativistic mass of quarks, moving at relativistic speeds. Quarks are quite light, but if we go deeper, the rest mass of quark is also an illusion - all particles have rest mass = 0, and what we call mass is...

This is just a revision question for an exam i have in a couple weeks. I think i kow the answer but just want to double check. a curling stone is released with an instial speed of 3.1 m/s the coefficent of sliding friction between the stone and ice is 0.017 What is the distance the stone...

My book points out that the combined rest mass of an isolated proton + an isolated electron is greater than the mass of a hydrogen atom: mH < mp + me The book then goes on to claim that if the electron is captured into the ground state in order to form a hydrogen atom, the rest mass...

I have came up some question asking the velocity change of the rocket in its instantaneous rest frame. And I have been taught that in the instantaneous rest frame, v=0, dgamma/dt =0, gamma = 1. if v is always zero, how come to talk about the change in velocity? Thanks in advance

So I have a simple lever that is connected to an extension spring. When the extension spring is exteneded it applies a force of 40lbs on the lever. The lever is 3 feet long and the pivot point is 1 foot from the top and 2 foot from the bottom. The lever weighs 2.1 lbs and has a 3lb weight...

Homework Statement A high speed proton collides with a proton at rest, two proton-antiproton pairs were created. That is some of the accelerated protons kinetic energy was enough to be converted into the mass of the new particles. If the proton-antiproton pairs move along together as a single...

what is "relativistic mass" and "rest mass".. as far as i know the rest mass is the mass which measured by an observer who is at rest relative to the object (please correct me if this is not right), if this is right... what if when the object is traveling at the exactly same velocity of the...

Is there actually a superfluous reason for rest mass. I only ask because clearly as far as I know, all particles have spin, and I am led, (possibly falsly) to assume that so do things such as photons (although we know photons don't have rest mass anyway). Thus if "everything" has spin, (lets...

I came across a book this afternoon called, "Einstein's Mistakes" by Hans C. Ohanian. If I'm remembering correctly, he said that the first error-free derivation of E=mc ^2 did not exist until Max von Laue produced one in 1911, and that it was based on "mathematical properties of the...

I'm sure I'm not thinking of this the right way. I'm hoping someone can see the error in my logic. Should a force have less of an impact on a moving object than one which is at rest? An object which is in motion has a momentum given by p=mv. A force F acting (say in the opposite...

Homework Statement The point on the bottom of a rolling object is instantaneously at rest (v = 0). What is the acceleration of that point? Homework Equations The Attempt at a Solution The formula given is a = \alphar, and r = 0. So I'm guessing it's zero as well, although that...

Hi there, Could anyone explain to me what is the different between the two terms (i) Original rest frame (ii) Instantaneous rest frame When do we prefer to work in the original rest frame but not the instantaneous one and why? And when do we prefer to work in the instantaneous rest...

Homework Statement A grasshoopper jumps 1.00 m from rest, with an initial velocity at a 45.0 degree angle with respect to the horizontal. Find the initial speed of the grasshopper (answer is 3.13 m/s) The maximum height reached (answer is .250m) Homework Equations...

Hello... learning to post and into the appropriate forums. Also, can you delete previous post and how? Quick question: Since time as we know it does not or can not 'stop'... Is there such a thing as an intertial frame at 'absolute rest'? Thank you for any and all responses. Bye G

Hello... If time stops at the event horizon of a black hole..which means there is no motion happening or can be observed..does that not mean that the centre of a black hole is a place of absolute rest? Could such a place of ab/rest 'move' thru the cosmos (basically a black hole which is a...

Homework Statement If two protons start out at rest relative to each other, separated by 0.1 nanometers in vacuum, and then they are released, calculate their relative positions after 10 seconds. Homework Equations F = (kq^2)/r^2 = m*a The Attempt at a Solution I am fairly...

Homework Statement David pushes on a .50 kg bottle of water with a force of 3.5 N (R). The coefficient of friction between the bottle and the desk is .20. Using the dynamics worksheet format below, find the acceleration of the bottle and how far it travels in 3.0 s if it starts from rest...

Is there a direct relation between the relativistic mass (total energy) and rest mass? In other words, can we say a proton has higher rest mass than an electron because a proton-antiproton annihilation would produce that much more energy than electron-positron one? And the ratio of energy...