# What is Relativistic speed: Definition and 32 Discussions

Relativistic speed refers to speed at which relativistic effects become significant to the desired accuracy of measurement of the phenomenon being observed. Relativistic effects are those discrepancies between values calculated by models considering and not considering relativity. Related words are velocity, rapidity, and celerity which is proper velocity. Speed is a scalar, being the magnitude of the velocity vector which in relativity is the four-velocity and in three-dimension Euclidean space a three-velocity. Speed is empirically measured as average speed, although current devices in common use can estimate speed over very small intervals and closely approximate instantaneous speed. Non-relativistic discrepancies include cosine error which occurs in speed detection devices when only one scalar component of the three-velocity is measured and the Doppler effect which may affect observations of wavelength and frequency.Relativistic effects are highly non-linear and for everyday purposes are insignificant because the Newtonian model closely approximates the relativity model. In special relativity the Lorentz factor is a measure of time dilation, length contraction and the relativistic mass increase of a moving object.

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1. ### I Question on the energy needed to go at a relativistic speed

Hello, I consider to be in a relativistic area, where an object is moving very fast, seen from our Earth, at a speed v where v is less than the speed of light c. I have considered the following equations (relativity equations) : T = β * t M = β * m L = l / β β = 1 / (√(1 – v2/c2) )...
2. ### Relativistic speed accelerator for physics experiments in a capsule

Is it technologically feasible today or in the near future, to accelerate in outer space a ~0.1 gram physics experiment lab, inside a cyclic accelerator and shoot it in a straight line at a constant speed of 5%-80% of the speed of light? That miniature capsule, must include all that is needed...
3. ### B Take on Length Contraction at relativistic speeds

Hello everyone and apologize if my questions seem a bit off, please have patience with me. I want to have the following, rather simple, thought experiment. Let's say that we have a moving object O with the proper length L, when at rest. Let's say that object O starts moving at 0.9c (90% the...
4. ### I Relativistic speed of a rocket with constant thrust

I try to calculate the speed curve of a relativistic rocket driven by a 100% efficient engine with constant thrust, when traveling to a distant star. All equations I can find consider constant acceleration, which of course is not working, since the ships mass decreases when the fuel is used...
5. ### B Length contraction applet - have they got it wrong?

Hi, I was browsing the internet for interactive simulations illustrating special relativity concepts. It seems to me that those in this http://kcvs.ca/concrete/visualizations/special-relativity are mostly nice and clear, although not very "chrome-friendly" (I have to use firefox to play their...
6. ### Finding the relativistic speed of a spacecraft

Homework Statement If a spacecraft is traveling to a star which is located at a distance of 1 lightyear and it would take the spacecraft 1 year to reach the star in its own frame, how fast would the spacecraft actually fly? Also, how long would the journey take for an observer on Earth...
7. ### Velocity of a spacecraft at relativistic speed

Homework Statement The closest star system is about 4.3 light years away from Earth. A spacetug is able to move a cargo ship at a constant force of g=9.8N/kg times the mass of the cargo ship for many years. Starting from rest, speed up the cargo ship until you're halfway to the nearest stars...
8. ### Gravity at relativistic speed

Is it possible to find the speed increase due to gravity pull using the SR velocity addition formula or the calculator here? http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel2.html Can you confirm that it is in accordance with GR formula? For example, if an asteroid is approaching the...
9. ### Relativistic speed of a particle

Homework Statement Find the speed of a particle whose total energy is twice its rest energy. Homework Equations E2 = p2c2 +m2c4 The Attempt at a Solution 4m2c4 = p2c2 +m2c4 3m2c4 = p2c2 SQRT(3)mc2 = pc SQRT(3)mc = p SQRT(3)mc = mv SQRT(3)c = v I know I can use E = gamma*mc2 to get the...
10. ### B Can a massive object have a velocity of c and zero mass relative to light?

I have a simple question on the relativistic view point with regard to light. From wiki, "All inertial frames are in a state of constant, rectilinear motion with respect to one another; an accelerometer moving with any of them would detect zero acceleration." Simply I understand if a physical...
11. ### B Magnetic field at relativistic speed

I am trying to understand magnetism and its relation to electricity: Suppose there are two electrons traveling side by side in deep space at 1 cm distance at .99 c In this article http://academic.mu.edu/phys/matthysd/web004/l0220.htm it is said that the ratio $F_B/F_E$ is $v^2/c^2$ for v <<...
12. ### B How Do Electron Orbitals Work at Relativistic Speeds?

So I was wondering... for no particular reason: Say you have a proton and your right arm is a particle accelerator. You throw the proton at about 90% the speed o' light. The you take your left arm which also happens to be a particle accelerator and you shoot an electron out right next to it...
13. ### B Can Force Change Mass w/ Constant Velocity?

can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible - ##\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}## where F is nonzero
14. ### B Gravitational Waves @ relativistic speed?

What would happen if I were to fly toward a gravitational wave pulse at relativistic speed? Would I be destroyed by the Doppler-shifted pulse? Would the wave become visible?
15. ### How Does Relativistic Speed Affect the Force Exerted by a Train on Rails?

I came up with this problem, which is non-trivial at least for me: Train accelerates with constant proper acceleration. When the speed of the train relative to rails is zero, rails feel the train exerting 1000N force on the rails. What force do rails feel the train exerting on the rails when...
16. ### Why do Jet fighter pilots experience a greater G-force?

Hi! I'm a high school student, aspiring to pursue a career in Astronautical Engineering. I always try and ponder on questions about everyday aerodynamics and physics. So, here's a question from you from an aspiring scholar. It is known that, at high velocities, pilots in super-sonic jet...
17. ### Relativistic Speed Travel: What is the Effective Speed?

Dear all, Let's assume I was planning an interstellar journey with relativistic speed. Being at rest on earth, the distance to the destination is ##d##. Let's further denote the proper time I will need to reach the destination as ##\tau##. Is there an official term for the effective speed...
18. ### Macroscopic Objects at Relativistic Speed

How much energy would be required to accelerate something the size of the space station to the same speed as protons colliding at the LHC?
19. ### Practice calculations for a relativistic speed object

Effects of a 150,000 kilogram object launched at Earth, just below the speed of light: 99.99999999999999 percent 'c' speed.The object weighing 150,000 kilograms gets a relativistic mass increase of 183,648,173,214,437,391 kilograms, therefore getting a relativistic energy of...
20. ### Potential Difference: Electron Accelerated to Relativistic Speed

Homework Statement An electron accelerated from rest through a potential difference V acquires a speed of 0.8c. Find the value of V. Homework Equations E=(gamma)mc^2, E=Vq The Attempt at a Solution For this I related the two equations above and chose a value of m=0.5MeV for the electron and...
21. ### Viewing a (giant) clock at relativistic speed

Can anyone answer this question? What you would see while watching a stationary clock that you are moving directly away from at a constant relativistic velocity? Yes, any practical clock would immediately shrink to a tiny point an instant after you passed it. So, either assume a really huge...
22. ### Relativity - Sphere flattening due to relativistic speed

Relativity -- Sphere flattening due to relativistic speed Homework Statement Gum balls are spherical, and about 1.5 cm in diameter. Smarties are circular in one cross section, with the same diameter, but perpendicular to this circular cross section, they are ﬂattened, with the smallest...
23. ### Magnetic field of straight wire, charges travels at relativistic speed

Hi there, Is it true that the magnetic field of a straight wire is the same when the charges are moving at low speeds (v <<c) as when they are moving at relativistic speeds (v~c). The extra relativistic factor the magnetic field gets from the moving charges cancels upon integrating. According...
24. ### Relativistic speed of an electron

Homework Statement Electrons are accelerated by a potential difference of 0.10 MV. Determine: a) The mass an accelerated electron b) The velocity of an accelerated electron The mass of the electron has been successful determined, which I give here. I was doing wrong when I was...
25. ### Microwave oven at relativistic speed

Imagine a microwave oven on some kind of track such that it can reach speeds approaching c. If the microwave was switched on and shot past us at a speed so that as it traveled away from us, the relativistic doppler effect shifted the emitted microwaves into the visible spectrum - What would we...
26. ### Exploring the Twin Paradox: Understanding Time Dilation and Relativistic Speeds

Okay maybe it's not just the Ender's Game series, and maybe its actually a cornerstone fact belief theorem postulation thing of relativity, but still! In the story Ender travels in ships which go at relativistic speeds. By doing so, centuries go past but he hardly ages at all. I don't get this...
27. ### Why are electric field lines straight around electrons moving at relativistic speed?

Imagine an electron in uniform motion moving at a speed near the speed of light. Pictures I've seen of the electric field around such a charge look like this one from wikipedia: The field lines are straight, but clustering around the plane perpendicular to the direction of motion...
28. ### What happens after you travel at a relativistic speed

If a spaceship is moving at a relativistic speed past the earth, the people on Earth would believe that the time in the spaceship was moving slower. The people on the spaceship would believe the time on the Earth was moving slower. So what happens when the spaceship stops? Do both times revert...
29. ### Time to travel at relativistic speed

I have a relatively simple problem that I'm having trouble with. A ship is going at 0.90 c, over a distance of 80 light years. In my text the method for determining the time spent traveling is: 80 years + (0.1 * 80) = 88 years This method seems logical, at 0.9 of the speed of light this...
30. ### High relativistic speed + entanglement

A thought exercise: You have entangled particles, leave one on Earth and put the other on a spaceship that is moving close to the speed of light. What happens when you change the rotation of one particle or the other? Given that the speed of light is the speed limit to the universe and that...
31. ### Relativistic speed involving particle decay

Homework Statement A particle of rest mass M0 is at rest in the laboratory when it decays into three identical particles, each of rest mass m. Two of the particles have velocity u1=-4/5c i(vector) u2=-3/5c j(vector) Calculate the direction and speed of particle 3Homework Equations pf-pi=0...
32. ### Solved: Relativistic Speed: Force of 30N Reaches 99% c in 7 x 10⁴ Sec

Homework Statement A particle of mass 1 gm starts from rest and moves under the action of a force of 30 Newtons defined in the rest frame. It will reach 99% the velocity of light in time (a) 9.9 x 10³ sec (b) 7 x 10⁴ sec (c) 0.999 sec (d) 0.7 sec Homework Equations The Attempt at a...