What is Clocks: Definition and 240 Discussions

A clock is a device used to measure, verify, keep, and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units: the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia.
Some predecessors to the modern clock may be considered as "clocks" that are based on movement in nature: A sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, a well-known example being the hourglass. Water clocks, along with the sundials, are possibly the oldest time-measuring instruments. A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.Traditionally, in horology, the term clock was used for a striking clock, while a clock that did not strike the hours audibly was called a timepiece; this distinction is no longer made. Watches and other timepieces that can be carried on one's person are usually not referred to as clocks.
Spring-driven clocks appeared during the 15th century. During the 15th and 16th centuries, clockmaking flourished. The next development in accuracy occurred after 1656 with the invention of the pendulum clock by Christiaan Huygens. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The mechanism of a timepiece with a series of gears driven by a spring or weights is referred to as clockwork; the term is used by extension for a similar mechanism not used in a timepiece. The electric clock was patented in 1840, and electronic clocks were introduced in the 20th century, becoming widespread with the development of small battery-powered semiconductor devices.
The timekeeping element in every modern clock is a harmonic oscillator, a physical object (resonator) that vibrates or oscillates at a particular frequency.
This object can be a pendulum, a tuning fork, a quartz crystal, or the vibration of electrons in atoms as they emit microwaves.
Clocks have different ways of displaying the time. Analog clocks indicate time with a traditional clock face, with moving hands. Digital clocks display a numeric representation of time. Two numbering systems are in use: 24-hour time notation and 12-hour notation. Most digital clocks use electronic mechanisms and LCD, LED, or VFD displays. For the blind and for use over telephones, speaking clocks state the time audibly in words. There are also clocks for the blind that have displays that can be read by touch. The study of timekeeping is known as horology.

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  1. R

    B Time dilation and 2 identical clocks

    Hi Couldnt figure this out U have 2 identical clocks where a pulse of light goes from a light source (a), reflects off a mirror (b) and goes to the end (c) A person is stationary wrt one clock and another clock is in a spaceship moving, relative to the observer, in the direction v at velocity...
  2. T

    B Time Dilation Effects: Hafele & Keating Experiment Revisited

    The experiment done by Hafele & Keating took clocks around the world in two directions and compared the readout to a static clock to measure time dilation effects. Everything fitted nicely with Einstein’s predictions. To avoid confusion let’s move the clocks way out in space to a real inertial...
  3. .Scott

    I Entangled Clocks: Exploring Possibilities

    I just overheard an engineer saying "There are no two clocks in the world that tell identical time". She was describing a time syncing mechanism to another engineer, but it made me think... In theory, can something large enough to be used as a clock become fully entangled with a copy of...
  4. E

    I Atomic Clock Running Rate: Adjustment Possibilities?

    Pendulum clock running rates can be adjusted by changing the length of the pendulums. Likewise the running rates of mechanical and electronic crystal clocks can be changed and adjusted. Can the running rate of an atomic clock also be adjusted? It doesn’t seem like there could be any way to...
  5. ISamson

    B Can Time Dilation Affect the Mechanical Functioning of a Clock in Orbit?

    Hello. I want to clear a doubt on Special Relativity, time dilation and clocks. If we get an accurate clock and make it orbit the, for example, Earth very, very fast, will the actual mechanical clock lag behind from the accurate clocks on Earth? The thing in this question is about the actual...
  6. E

    B Synchronize Clocks in Relative Motion: How & Why

    Is there any way to synchronize two clocks already in relative inertial motion? If so, how? And I am not sure exactly what “synchronize” would mean in that context. Maybe it would mean that their readings, or at least their running rates, would match when their relative motion was stopped? There...
  7. R

    B 2 clocks -- Using orthogonal light path detectors in a space ship

    Hi I can't see the error in this can someone please explain where I went wrong? A man is in a spaceship traveling at a constant velocity He makes 2 identical tubes of length L with a mirror at one end, tube a and tube b He has a single light bulb. Next to the bulb is a detector. He carefully...
  8. E

    I Mechanical clocks and time dilation

    Does anyone know if any mechanical clocks have ever been accurate enough to show time dilation? (That would be a clock with a spring-mass harmonic oscillator.) Is there any reason to suspect they might not show the same thing as the atomic clocks? (Pendulum clocks would not, for example. They...
  9. Pushoam

    I Time Dilation, Clocks, & Gravity

    In the rest frame , the measured time interval is the time elapsed between the two ticks (so two events T1and T2) of one clock. In moving frame,the time elapsed between the two ticks T1and T2 are measured by the two synchronized clocks kept at two different places x'1 and x'2. The...
  10. Bob Walance

    I Two Clocks Orbiting a Non-Rotating Planet: Questions Answered

    Two clocks A and B are orbiting a non-rotating planet. Each clock periodically transmits its current time value via a radio signal and the other can receive that value. Their orbits are in closely-spaced parallel planes and both orbits are the same distance from the planet. The two clocks are...
  11. JulianMau

    I Clocks ON a rotating disk: What happens?

    I was reading about the Ehrenfest Paradox and it got me thinking about something (that I think is) similar: Suppose we take a large, flat, and rigid disk, and we attach to various parts of it a number of clocks (some very close to the center of the disk, some along the edge, others in between)...
  12. J

    B DeltaT of clocks at endpoints of a rocket post acceleration

    Following scenario: A rocket measuring 10 lightseconds in length accelerates near instantaneously to v=0.4c. Pre-acceleration two clocks placed at the endpoints of the rocket were synced. What will be the time difference between the two clocks post acceleration? I tried to figure it out...
  13. Auto-Didact

    A Weinberg: detecting changes to QM using atomic clocks

    Steven Weinberg has lately been critical of QM. He now also has a technical paper out called 'Lindblad Decoherence in Atomic Clocks', available on arxiv. Here is the abstract: It's a short paper (6 pgs of text), arguing for objective collapse (a la GRW/Diosi-Penrose/etc) instead of...
  14. Rishi Tharun

    B Synchronized Clocks: Will They Remain in Sync Forever?

    Will the synchronized clocks placed in an inertial frame remain synchronized forever?
  15. Algr

    Is "Centon" copyrighted? (metric clocks)

    Is the term "Centon", as a unit of time used in Battlestar Galactica copyrighted? How would I go about finding this out? I was thinking about how people would deal with measuring time on other planets when I got to thinking about decimal time and what the units were called. Using seconds...
  16. Tazerfish

    B Derivation of time dilation without light clocks

    In the way I was taught about special relativity, time dilation is like the fundamental building block from which you derive things like relativistic mass and length contraction. So it has always struck me as quite odd, that the derivation of time dilation (in some sense the basis of special...
  17. robphy

    Insights Spacetime Diagrams of Light Clocks [comments]

    A new entry for Physics Forums Insights has been posted https://www.physicsforums.com/insights/spacetime-diagrams-light-clocks/ For now, please use this thread to comment.
  18. P

    I Special relativity of two clocks

    Why is it that for two clocks that are synchronised in one frame, S, but not in another, S', is there an offset in the time by a factor of ##\frac{Lv}{c}##, as measured in S'. Where L is the proper length of the body, as measured in S. I'm confused as to why there is not a factor of ##\gamma##...
  19. G

    I 2D Time dilation simulation with several clocks?

    Hi, I'm looking for some kind of simulation for time dilation where you can add several clocks to a 2D plane, synchronize them, give them velocities and accelerate them. For example to simulate the twin paradoxon including the acceleration necessary to (at least) one clock to reunite them. I...
  20. A

    Where Will the Clocks of John Harrison Go Next?

    For those few of you close to Mystic, CT I would like to mention that the Mystic Seaport Museum has a exhibit on the clocks of John Harrison. It is closing March 28 so there is not too much time left. Here is a link http://www.mysticseaport.org
  21. A

    How to synchronize clocks in accelerating frame?

    I don`t understand how synchronization of clocks can be made in an accelerating frame. let`s put a source of light at the center of an accelerating rocket. From it, many pairs of pulses are emitted one at a time in two opposite directions. Because the source is located at an equidistant from two...
  22. L

    B Why aren't standard rods and clocks affected by LC and TD?

    Are measuring rods and clocks(the ones that are used as reference to ascertain LC and TD of the relatively moving rods and clocks) left out of the theory in principle?
  23. A

    I Exploring the STR Argument: X & Y's Clocks

    I am hopeful someone can give me a quick lesson here. I have an idea that time does not slow as one's velocity increases (bear with me, please). I'll state this in familiar terms with a person on a train vs platform and the light beam traveling vertically from the ceiling (P1) to the floor of...
  24. L

    Gaging Time with Chemical Clocks: A Crazy Idea?

    I am really very new to chemistry and physics, although I hope to study in the future. I have a question regarding chemical clocks. Is it possible to gage time using a specific chemical clock or chemical reaction that you may know of? my first,idea was standard chemical clocks like the...
  25. E

    Signal time in Twin Paradox: Fast clocks? Redshift/blueshift

    NOTE: This is NOT a homework problem. I created this one myself based on some problems I have seen, with specific numbers used to make calculation clean and easy. Tl/dr version: in a round trip to a star, will the "moving clock" run slower on the way there but faster on the way back due to the...
  26. Raymond Potvin

    B On light clocks and reference frames

    I had this questioning about the light clock on another thread, and DaleSpam suggested that I open my own thread, so here it is. I was asking if the light clock mind experiment was not contradicting the reference frame principle. I added that to my drawings: And DaleSpam answered this: So...
  27. B

    Clarification on synchronous clocks

    Kind of long winded, but I would appreciate a second veiw on untangling EA's thinking about this. § 2. On the Relativity of Lengths and Times We imagine further that at the two ends A and B of the rod, clocks are placed which synchronize with the clocks of the stationary system, that is to say...
  28. D

    Synchronized clocks in a moving frame

    Homework Statement It is not a homework question.I am trying to understand the concept in the attached diagram but I stuck.Hope someone can help Homework EquationsThe Attempt at a Solution Please see the lower part of the note,stating that Δt' = Δt/γ.However,imagine you are in the moving frame...
  29. E

    B Is time dilation just a problem with our clocks?

    [Mentor's note: This thread was split off from https://www.physicsforums.com/threads/time-dilation-and-redshift-for-a-static-black-hole-comments.835277/ as clarifying misunderstandings about time in general is off-topic in a thread about the specifics of time dilation around a black hole]...
  30. S

    The Mysterious Synchronization of Clocks in Special Relativity

    Let's say we have a clock that work like this , districts beam of lights are sent in constant time gaps (created by a crystal or some other radioactive process) to a sensor. the sensor is connected to a counter that counts the number of beams, and here we have our clock. Now if we put 2 clocks...
  31. afcsimoes

    Huygens synchronization of two clocks

    This is the title of a new paper published by two Portuguese scientists (see http://www.nature.com/srep/2015/150723/srep11548/full/srep11548.html or http://www.nature.com/srep/2015/150723/srep11548/pdf/srep11548.pdf). They developed a math model of the synchronization of the two clocks and the...
  32. J

    Do clocks measure conformal time?

    Assuming the spatially flat FRW metric for simplicity: $$ds^2=c^2dt^2-a(t)^2(dx^2+dy^2+dz^2)$$ where ##t## is cosmological time, ##a(t)## is the scaling factor and ##x,y,z## are co-moving Cartesian co-ordinates. Light freely propagating along the ##x##-direction follows the null geodesic, with...
  33. J

    Light clocks measure conformal time - detailed argument

    Let us assume that an observer is stationary at the origin in expanding space. We assume the FRW metric near the origin is given by: $$ds^2=-dt^2+a(t)^2dr^2$$ Let us assume that the observer measures time by bouncing a light beam at a mirror that is at a constant proper unit distance away from...
  34. 1977ub

    Near-instant Acceleration / Clocks

    If I have a "train" at the "platform" and wish to send the train accelerating to near-C velocity in near-zero time from my frame. I presume that there is no theoretical limit on the acceleration (as far as SR goes). I presume that the clocks throughout the train will all appear barely to...
  35. 1977ub

    Clocks Within Each Ship in Bell Spaceship Paradox

    I believe length contraction always makes more sense when integrated with reminders of relativity of Simultaneity. Let's say the engines are at the back end of each rocket. For the viewer "A" in the initial frame, they begin moving and continue accelerating simultaneously, and clocks next to...
  36. L

    Can we use a light clock to measure the accuracy of another clock?

    I was looking at this because well i wanted to. http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_clocks_rods/index.html And i worked something that if it was right i would be fantastic. But i can't really believe its this easy.
  37. 1977ub

    Time Passes Faster: Moving Frame w/ Many Clocks

    I had asked this about 2 years ago - but for the life of me cannot find it. Please feel free to cancel this if you can find my OP. Anyhow my question was this: A "train" passes by at significant relativistic speed, along the "x" axis. "Platform" observer peers in windows of train as it passes...
  38. S

    Can clocks ticking at different rates be synchronized?

    I was reading an article about synchronizing clocks on the rim of a rotating disc with a central, inertial clock. I was wondering how is this possible or have I misinterpreted something. Clocks on the rim tick slower than the central clock because they move relative to the center, so I don't...
  39. Chronos

    Using atomic clocks for gravitational wave detection

    This paper, http://arxiv.org/abs/1501.00996, proposes using atomic clocks for gravitational wave detection. It sounds similar to other ideas involving pulsar timing experiments. The twist here is utilizing satellites to provide a wide base for improved sensitivity. Sounds like an inexpensive...
  40. mpx86

    Clocks and their relative speeds

    Homework Statement A watch gains 3 minutes every hour. If it is set right at 11 a.m. on February 21st, 2012, when will the hour hand of this defective watch and a correct watch be at the same position? A) 9 p.m. on February 21st, 2012 B) 11 p.m. on February 28th, 2012 C) 11 a.m. on March 2nd...
  41. I

    Mapping Space with Clocks: Deduce Distances/Observers w/ Constant Light Speed

    Suppose that we do not have any way to measure distance, but do have clocks. There are N observers, who can all see the distant events, say spaceships taking off and landing on far away planets. The question is: assuming the speed of light is constant, can we deduce the distance to the events...
  42. S

    Derive Phase difference between clocks with distance

    Phase difference between clocks with distance Homework Statement Derive Phase difference between clocks with distance Homework Equations I honestly don't understand how this equation ΔT = vD/c2 is derived/figured out. The Attempt at a Solution We haven't covered Lorentz...
  43. Newcopernicus

    Clocks and Gravity: How Earth's Movement May Affect Timekeeping

    If time is being warped by gravity/accelerated motion, does that mean that our clocks are inevitably slowed down since the Earth's constantly moving
  44. nsaspook

    Safety countdown clocks at intersections.

    This is a fascinating display of how humans react to increased information while driving. I've noticed that I also react to the knowledge of how long the light will stay on with counters but never really thought about how it could cause accidents...
  45. S

    Special Relativity and Biological Clocks.

    Hi. So the whole premise of special relativity seems to me to be hinged on the immutability of the speed of light, the fact that it is the same for every inertial frame of reference, and the fact that information and energy cannot travel faster than this. What really puzzles me is this whole...
  46. J

    Do clocks speed up in an expanding Universe?

    For simplicity I assume a flat radial FRW metric (with c=1): ds^2 = -dt^2 + a^2(t)\ dr^2 Now let us consider the path of a light ray, a null geodesic, with ds=0 so that we have: dt = a(t)\ dr Now at the present time t_0 we define a(t_0)=1 so that we have: dt_0 = dr The interval of radial...
  47. E

    Can baseballs truly synchronize clocks ?

    Einstein defined truly or absolutely synchronous clocks as follows: "The simultaneity of two definite events with reference to one inertial system involves the simultaneity of these events in reference to all inertial systems. This is what is meant when we say that the time of classical...
  48. C

    How do Gravity and Acceleration affect Clocks?

    I read that stationary clocks on Earth experience time more slowly than clocks on GPS satellites, so the GPS clocks are calibrated to run more slowly to compensate. Since the satellites are in orbit, wouldn't that mean their clocks would be slower since they were moving faster?
  49. ShayanJ

    SR and synchronization of clocks

    Einstein's article "on the electrodynamics of moving bodies", starts with talking about synchronizing clocks at different places and it is through this that Einstein explains concepts like time dilation and length contraction but in the present books about SR you hardly find things about...
  50. J

    Can Atomic Clocks Measure Time Accurately Underground?

    Have there been any experiments using atomic clocks underground as a comparison to those on the Earth's surface?
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