Reference Definition and 1000 Threads

My question is about time-space. It seems to me that special relativity measures time based on light and derives its conclusion on that base. If my understanding is correct, why should we rely on light to measure two moving clocks? Must we involve light when talking about time? What if light...

Hello all - New to the forums so let me start by saying hi to everyone. ;) Something has always bugged me about considering entanglement effects as "instantaneous." As we all know from SR, moving observers do not agree on simultaneity between two space-separated events. If we...

Homework Statement Consider a body falling from a tower in the northern hemisphere at approx 40 degrees latitude. The body is seen to have a displacement to the east. Explain the origin of this displacement qualitatively from the point of view of a non-inertial observer. What local effect is...

Hello I am new to this forum and I just wanted to post about a paper that I found in Physical Review Letters. It is in Volume 90, number 20, 201102 (2003). It is titled "Traversable Wormholes with Arbitrarily Small Energy Condition Violations", by Matt Visser et al. In this paper, it is...

Does anyone happen to know of a good reference for ASTM A572 (any grade) that lists temperature effects on yield? The standard only lists room temperature specs. Thanks

Homework Statement Through simple harmonic motion produced on a trampoline Ivan ossilates freely, with a period of 0.85s. On a reference circle show Ivans position after 1/8th of a cycle. Label (and solve) the distance of this position from the equilibrium position.(Max displacement is...

My problem is related to the Brookhaven experiment of the J/psi discovery and the Y discovery at Fermilab (in both cases, protons over a Berillium fixed target). In both cases they had a resonance decaying into two leptons, and the detecting system consisted of two arms, covering a relatively...

Hi, I am currently a 3rd year electrical engineering student and I will looking for 12-16 month co-op/internship following the completion of this year. I have received some reference letters from my professors and just wanted to know, is it advisable to include one or two along with my resume...

Kinetic energy is 1/2mv^2, and velocity varies depending on velocity of the observer, so does kinetic energy also vary depending on the velocity of the observer? for example, someone sitting in a bus who slides a 2 kg brick down the center isle of the bus at 5 m/s could say the has a kinetic...

does an object with constant acceleration follow Newton's laws? with constant velocity? a stationary object? i think the last two are true, but I'm confused whether a constant acceleration (m/s/s) of whatever still applies to an inertial frame or is a noninertial frame? because in a sample...

Homework Statement There is a planet of mass m_1 orbiting a star of mass m_2. One question is "What is the semimajor axis of the planet's orbit in the coordinate system centered at the star's center", and another is "What is the semimajor axis of the planet's orbit centered at the center of...

Homework Statement Hi, My question probably has a simple answer, but I've been scratching my head over it a little too long so I thought I would ask it here. I have three initial photons involved in a collision with 4-momenta k1, k2 and k3. I have two reference frames: frame 1: the...

Hi, My question probably has a simple answer, but I've been scratching my head over it a little too long so I thought I would ask it here. I have three initial photons involved in a collision with 4-momenta k1, k2 and k3. I have two reference frames: frame 1: the centre of mass frame of...

1. The Question Verbatim "A pilot starting from Athens, New York, wishes to fly to Sparta, New York, which is 320 km from Athens in the direction 20.0 N of E (LETS CALL THIS VECTOR = A). The pilot heads directly for Sparta and flies at an airspeed of 160km/h. After flying 2.0 h, the pilot...

This seemingly-easy reference problem is making me crazy! The airport terminal has a moving sidewalk to speed passengers through a long corridor. Larry does not use the moving sidewalk. He takes 145 s to walk through the corridor. Curly, who simply stands on the moving sidewalk, covers the same...

Came across the following interesting problem : Two explosions take place at the same place in a rest frame with a time separation of 10 s in that frame. A) Find the time between explosions, as measured in a frame moving with a speed 0.9 c with respect to the rest frame according to...

Suppose an empty space and two points. The distance from point A to B is d = k . t^2 k=constant t = time The question is: Which point is an Inertial Frame of reference ? Suppose an empty space and two references frames. A is rotating at w with center B. But B is...

A ball is thrown with initial speed vo up an inclined plane. The plane is inclined at an angle(fi) above the horizontal, and the ball's initial vecity is at an angle (theta) above the plane. Choose the axes with x measured up the slope, y normal to the slope and z across it. Write down Newton's...

I am standing (yes, the question actually goes like this!) on a level floor at the origin of an inertial frame S and kick a frictionless puck due north across the floor. a.) Write down the x and y coordinates of the puck as functions of time as seen from my inertial frame. (use x and y axes...

Homework Statement Two events happen at the same point x'(0) in frame S' at t(1)' and t(2)' a) Use equations x=gamma*(x'+vt') and t=gamma*(t'+vx'/c^2) to show in frame S the time interval between the events is greater than t(2)'-t(1)' by a factor of gamma Homework Equations The...

what is an inertial frame of reference ? Simple ?

Homework Statement Consider a head-on, elastic collision between two bodies whose masses are m and M, with m << M. It is well known that if m has speed v0 and M is initially at rest, m will bounce straight back with its speed unchanged, while M will remain at rest (to an excellent...

This is the question: A physics lecture demonstration uses a small canon mounted on a cart that moves at constant velocity v across the floor. At what angle theta should the cannon point (measured from the horizontal floor of the cart) if the cannonball is to land back in the mouth of the...

In the link: that I found here 5 minutes ago ( thanks for the link ) there are two drawings: the first and the second. In the first the link explains that there is a magnetic field, because the - charges are moving. In the second the link explains that there is not a magnetic field...

Hey all, I made a post earlier today on gravitational time dilation. It got me thinking that in any accelerated frame of reference there must also be a time dilation, due to the equivalence principle. This can simply be a elevator accelerating through space or it can be caused by centripetal...

Hi I'm using thermocuple as a temp. sensor, it is inside soldering handle output is 0 mV (tested with digital voltmeter at range 200 mV) at room temperature. I'll amplify that voltage using AD623 I cannot use Ice bath to set ref. junction at 0 deg C. I thought using table (ref junction at 0 deg...

In an anniversary celebration of Marilyn Bell's 1954 crossing of Lake Ontario a swimmer set out from the shores of New York and maintained a velocity of 4m/s [N]. As the swimmer approached the Ontario shore, she encountered a cross current of 2m/s [E 25deg S]. Find her velocity with respect to...

What forces affect on the Moon in the Inertial frame of reference which is the Sun? +gravity form the Sun +gravity from the Earth +centrifugal force from the rotationary movement of the Moon round the Earth is this list correct?

Hi. What's a standard reference for physicsts concerning the topic of fluid dynamics or computational FD.

I was just wondering about the following problem. Suppose that you have an arrow placed in a tube. If the arrow travels at a relativistic speed, does there exist a frame of reference such that the arrow is completely in the tube with extra tube at its ends? Does there exist a frame of...

Hello, Every definition of an inertial reference frame that I have read stated that it is a frame in reference in which Newton's laws are valid. But is it possible to define it in this way: it is a coordinate system that is not accelerating relative to some absolute reference point. Is there...

I'm trying to call a function from a .o file, and it keeps telling me: "undefined reference to ..." where the ... is whatever function I'm trying to call. Do any of you have any idea what's wrong with this?

Why does an object far away looks like it's going very slow when it's going really fast? And then the object seems really fast when it's near me. I just started driving and I always try to find an answer but really can't. Thanks :)

One way to attack a satellite in Earth orbit is to launch a swarm of pellets in the same orbit but in the opposite direction. Suppose a satellite in a circular orbit 500km above Earth's surface colides with a pellet having a mass of 4g. What is the KE of the pellet in the reference frame of...

Hi I am searching for some kind of mathematical "reference". My math knowledge is mainly from a five year technical school and some basic university courses. I can solve equations (linear and differential), use vectors and matrices, use geometry in 2/3 D, use probability and statistics...

A friend and I have been discussing what we think is an error in our textbook (either that or a misunderstanding on our part). The book gives an example in which two protons are initially traveling parallel to one another in the same direction with equal velocity. We think that since the...

Homework Statement A rubber stopper of mass 25g is suspended by string from a handrail of a subway car traveling directly eastward. As the subway train nears a station, it begins to slow down, causing the stopper and string to hang at an angle of 13 degrees from the vertical. What is the...

Sorry for the trivial (and certainly already covered) question. Does a body's weight change with the ref. frame? If I had a very long scale on which the body can move without friction, would I observe the scale to sign different values according if I am stationary with the scale or with the object?

Homework Statement The steel ball is suspended from the accelerating frame by the two cords A and B. The angles (they are on the inside) are both 60 degrees. Determine the acceleration of the frame which will cause the tension in A to be twice that in B. The acceleration is going to the...

Hi I know that the following can never be done in the real world, but in theory, if the vectors of all particles, antiparticles, photons etc. in the universe could be summed, would that qualify as an absolute reference frame for that instant in time? Clearly each instant would have a...

Hi I'm in the middle of writing up the Frank-Hertz experiment as part of my lab module this year, but I'm having trouble finding a 'reliable' website that I can use to quote the electron energy value (ie 4.9eV). I'm afraid my lecturer refuses to acknowledge wikipedia as a good source...

For those of you who don't know, "Formulas and Theorems" is basically a compilation of thousands of math theorems, 6000+ formulas, with a summary of their proofs, covering most of what was known in the late 18th century. What I'm looking for is a comprehensive reference book with worked...

I've seen several responses (and links) to the question "What happens when something is traveling at the speed of light" and understand that the answer is twofold. First no object can travel that fast because it would require an infinite amount of energy to acelerate physical objects to that...

so here r ma doubts => it is sometimes heard tat inertial frame of referance is only an ideal concept and no such inertial frame exists.comment. =>the accelaration of a particle is zero as measured from an inertial frame of referance . can we conclude tat no force acts on it? => a...

Does anyone know or have a reference indicating what PLC [programmable logic controller] brands are popular in China?

Suppose event A causes event B. To one observer, event A comes before event B. Is it possible that in another frame of reference event B could come before event A? If so, how?

Since in our proper frame of reference the fall of material into a black hole would appear to take for an eternity, would it not follow then that all black holes would appear as these instead? Would in fact all black holes appear this way? What if you have a small black hole and then have...

I'm having trouble writing out a reference for a book. My normal format is: Author (year of publication) Title publisher, place of publication eg: Trueman, A.E. (1949) Geology and scenery in England and Wales. Penguin Books, Harmondsworth This book is a revised edition, revised without help...

Our planet is moving through our solar system and our solar system is moving through our galaxy and our galaxy is moving within the local group and are local group is moving through our universe, so how fast are we moving right now, and if i then jump into my spaceship and accelerate am i...

Simple question. Are reference angles always positive??