What is Clocks: Definition and 241 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. askingask

    How to input and output work in a system at the same time?

    Basically, I thought of a weight as a energy storage. But realised you have to output that energy from the same part that inputs the energy. Now I have done some research and found two ways of storing and discharging mechanical work at the same time. First is the Huygens mechanism(maintaining...
  2. C

    B What does symmetry of time dilation really mean?

    Hello everyone, I've been studying Morin's book and the case for time dilation makes sense, a clock in the rest frame of the moving body counts to ##T_A##, and a clock in the lab frame counts to ##T_B## and we find ##T_B = {\gamma}{T_A}## What I might be failing to do is understand what the...
  3. P

    I Clock Synchronisation -- Do clock speeds go out of synch?

    When reading about the one way speed of light, I think it's fair to say that most potential methods to obtain this fail because it is said to be impossible to have two non co-located clocks in synch. My question is really about terminology. Normally, two things can be said to be in synch if...
  4. DiamondTiara

    I Telling time on Iapetus and other general questions about Iapetus

    I have some general questions about Iapetus here that I came up with. I have been very interested in Iapetus, the third largest moon of Saturn lately. 1 - How would clocks work on Iapetus? It orbits Saturn once every 79.3 days and is tidally locked to the planet. What would a time keeping...
  5. H

    I "Quasar clocks" and time running slower long ago

    Regarding the new "quasar clock" data showing that time ran more slowly (~5-fold) shortly after the Big Bang: is it all based on the periodic variation in luminosity at various wavelengths of some quasars (and presumably explained by the special relativistic time dilation effect from "spatial...
  6. P

    B How to compare the proper times of two spatially distant mass points?

    Do all synchronized clocks in a reference system always show the same time? Is this part of the definition of a frame of reference? Have the clocks always passed the same proper time from zero (see below)? Would the knowledge of the proper time of a clock between two events lead to the...
  7. D

    B Time dilation in a planet-moon system

    In Wikipedia time dilation is considered: As far as I know, in a planet-moon system, the difference in elapsed time between a clock on the planet and a clock on its moon is calculated using GR/proper time, so it's not very obvious if/how the movement/velocity of the moon around the planet...
  8. D

    I Relevant/irrelevant clocks for experimental tests of relativity

    Recently, in this forum, highly respected members referred to clocks like pendulum and hourglass as if they are relevant for relativity. Are they really? Besides the lack of accuracy, they depend on acceleration/gravity, so they would not work at all in inertial frames and they could not...
  9. Killtech

    I Time Measurement in Extremely Curved Space Regions

    In the beginning, there was time - at least within the SI system. Second is the first unit defined and it has no dependency on any other unit and is only defined via a physical entity, a Caesium 133 hyperfine transition frequency. Since clocks aim to meet that standard, it effectively is a...
  10. A

    B The synchronization of clocks and the relativity of motion

    In his thought experiment on the relativity of simultaneity, Einstein synchronizes two clocks A and B (at either end of a rod) to the clock C in a stationary frame, while A and B (the rod) is moving relative to C. The equations Einstein finishes with demonstrate how observers moving with A and...
  11. H

    What Was Clockwise Called Before Clocks Existed?

    What was clockwise motion called before the dial clock became well known? https://historyqa.com/how-did-people-refer-to-clockwise-and-counterclockwise-before-clocks/ In Northern Europe, the sun was perceived as moving in an arc from left to right. The farther north one goes, the more that is...
  12. H

    Clocks On a Hyperdimensional Planet

    On a planet with four spatial dimensions and one of time a clock would look like this. The hands are connected with pivots. The height of the jewel corresponds to the height of the Sun in the sky. If it is above white then it is daylight, if above black it is night. Here the sun has height...
  13. J

    Electrical Quartz Clocks (Battery Operated)

    I never had quartz clock I see you need to use carbon battery, I am thinking start with 1000 ohm resistor and see if clock runs with alkaline battery if not just keep lowering resistance.
  14. K

    I Measuring Time & Spatial Distances: Timelike vs Spacelike

    My book writes " The geometric distinction between timelike and spacelike distances is mirrored in the devices used to measure them. A clock is a device that measures timelike distances; a ruler is a device for measuring spacelike ones. Two nearby points or a timelike world line are timelike...
  15. M

    I Understanding Simultaneity Through Male & Female Clocks Meeting

    This is not a homework question, just a scenario I've come up with. Imagine I have a male and a female clock moving towards each other. If they're in sync, one will fit inside the other and they'll continue on their way. If not, they'll collide. (Apologies for the crude drawings.) I place these...
  16. S

    I The Derivative Nature of Time and Its Relation to Earth's Rotation and Speed

    I tweeted this on a Sabine Hossenfelder’s Twitter thread: Is there an example, definition, explanation of time that is not derivative of a physical system like a clock, e.g., that's based on the rotation of the earth? If not. If time is not a stand-alone definable entity how can it qualify as a...
  17. R

    I Light Clock Relativity: Why Divide T_moving/T_stationary?

    In special relativity I can get ## \gamma ## , ## \frac {T_B}{T_A}=\gamma ## Why do I not go ##{T_B} - {T_A} = \gamma## ? ##T_B = \frac {2H} {c^2 - v^2}## . ## T_B ## is the moving light clock. ## T_A = \frac {2H} {c^2} ## . ##T_A ## is the stationary light clockI assume LaTeX doesn't work...
  18. T

    B Time Dilation on Rotating Disk: Clocks on Disk Perspective

    Obviously, a third observer who is at rest with respect to the disk will see that the clock on the outside has a much faster velocity than a clock on the interior of the disk, so clearly the outside clock will show that it has measured less time. But that's one question. What about looking at...
  19. C

    I Building Quantum GR out of quantum rulers and quantum clocks

    Hi, has anyone tried to build "quantum GR", using the expectation value of |Psi(x)> as a "quantum ruler" and |Psi(t)> as a "quantum clock" to build up the idea of a "quantum metric"?
  20. hutchphd

    I Simultaneity of accelerated clocks

    <Moderators note: split from https://www.physicsforums.com/threads/is-the-relativity-of-simultaneity-more-than-just-a-fudge-factor.1012027/#post-6596771 > I have a (probably) stupid question. My rest frame contains myself and the usual rigid 3D array of clocks. I use Einstein's method to...
  21. phoenix-anna

    I Applications of the proposed global quantum network of clocks

    Physicists have proposed linking a global network of cesium clocks in a phase-coherent entangled state, for example in the article A Quantum Network of Clocks (arXiv:131045v1). My audience would like to know how better synchronization or more accurate timekeeping would lead to advances in our...
  22. S

    Time measured by two clocks (involves time dilation)

    Proper time (to) is the time interval between two events measured by an observer who sees the events occur at the same point in space. I am confused how to determine which one is proper time for this question. How to know which events occur at the same point from the question sentence? Thanks
  23. S

    B Time Dilation Effect: Corrections to Clocks on ISS

    Hello All The Hafele-Keating experiment in 1971 confirmed measurable time dilation effects on atomic clocks flown around the Earth on aircraft. Presumably clocks aboard the International Space Station suffer worse time dilation because of their greater speed in orbit. How often are corrections...
  24. G

    I Leading Clocks Lag: Twin Paradox Explained

    . . Two distant observers at rest with one another synchronize their clocks utilizing the travel time of light (by first moving the clocks to their locations, then using a light signal to time when the second clock should be turned on, and setting the second clock ahead to account for the...
  25. Buckethead

    B Clocks Vanishing into Thin Air - Gravitational Time Dilation

    With regard to relativity of simultaneity and the "block" universe and reflecting on the notion of skewed time slices associated with frames moving relative to each other, one observer sees one event a distance away (parallel to the direction of motion) occurring before another event a distance...
  26. cianfa72

    I Reference frame vs coordinate chart

    Hello, here on PF I've seen many threads about the concepts of 'reference frame' and 'coordinate system'. In the context of SR my 'envision' about the concept of 'frame of reference' is basically the 'rods & clocks latticework' as introduced in the book Spacetime physics (Taylor, Wheeler)...
  27. Kairos

    B Twin Paradox: Radioactive Decay Tested

    If two identical radioactive masses were subjected to the "twin paradox" experiment of Langevin, would the mass that traveled be really less radioactive than the one that did not? Radioactive decay is supposed to be independent of physical conditions and to only depend on the isotope.
  28. Muthumanimaran

    B How trapped ions can be used to make Atomic clocks?

    Can someone explain me conceptually how one can use trapped ions to make atomic clocks? My basic understanding of trapped ions is, we can think of an ionized atom which is controlled by electric and magnetic fields. But i am wondering how can one build an atomic clock using trapped ions.
  29. Martian2020

    B Please gradually expain principles of atomic clocks

    Atomic clocks. I tried to read wiki, read some QAs (on stackexchange), use web search. I would spend way much time to link all together alone, so I ask your help. I'm not sure if its called top-down or bottom-up. 1) Principle 1. Please confirm (or correct) my understanding of 1st underlining...
  30. Grimble

    B What Causes Moving Clocks to Measure Slower? Explained

    After much deliberation I can finally see and understand what you have all spent so much time and patience explaining to me! I can see that to observe the 2nd postulate; 'the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source or observer' a...
  31. D

    B The Fourth Dimension: A Measurement of Aging

    What Do Our Clocks Read? It is said that when asked- “what is ‘time’?”- Einstein once replied, “Time is what our clocks read”. But what do our clocks read? One may easily reply to this question- our clocks read ‘Time’. But isn’t it a circular argument? We can understand it by an analogy. If...
  32. M

    Global Positioning System / Clocks in Space

    I'm a bit lost at how to exactly start this exercise... As far as I understand we need to first determine ##d\tau_E## and ##d\tau_S##. First question: Since we can neglect the Earth's movement, can I also neglect the movement of the satellite with respect to the far away observer? If so, I...
  33. George Keeling

    I Why do clocks show proper time?

    I often see the assertion that clocks show proper time. (E.g. this thread). But I don't think that I have seen a good reason for the assertion in GR. It's not a problem in SR because one can always find a coordinate system that is stationary relative to a clock so, from the metric, ##...
  34. alexmahone

    Prove that “leading clocks lag”

    Homework Statement: A spaceship has two clocks: one in the front and one at the back. The clocks are synchronized in the spaceship's frame of reference. The spaceship zooms past the Earth's surface at a relativistic speed. Prove that in the Earth's frame of reference, the clock at the front...
  35. M

    B Can I keep multiple clocks in sync after a ride on a roller coaster?

    Suppose there are 6 cars on a roller coaster and I synchronize 6 clocks at rest with respect to each other in a box with no wiggle room on the space station. The bottom of the box has the same shape as the curvature of the earth, and the box is always kept "top side up" with respect to the...
  36. Foppe Hoekstra

    I Is it possible to have synchronized clocks in a rotating system?

    Consider a wagon with length L and constant speed v on the straight part of a rail. The wagon has clocks on both ends that are sync in the co-moving frame (of the wagon and the clocks). Then there is a curve in the rail with radius r. The speed of the wagon in the curve is still constant v, but...
  37. Foppe Hoekstra

    I Do clocks on Bell’s spaceships stay synchronized?

    If both of Bell’s spaceships have a clock that are synchronised when the spaceships are at rest, will they still be synchronized in the moving frame of the spaceships, after the spaceships are accelerated to a (the same) constant speed? (Personally I think they do, but I often seem to think...
  38. N

    How can the time dilation equation explain faster moving clocks running slower?

    Since for the two events of Samir starting the stopwatch, and the stopwatch reaching 10.0s, Samir and his stopwatch are stationary from his own frame of reference, I said it was the proper time and that delta t0 = 10s. Then the speed of the moving frame of reference was 0.6c. I thought placing...
  39. iVenky

    I Why are atomic clocks so accurate?

    For any clock, the way I define accuracy of the clock is based on the Q factor (the ability to reject noise) and the inherent noise in the system. In that case, can you explain me why atomic clocks are so accurate? Do they have high Q factor? (if so, how)? or low noise to begin with?
  40. Zack K

    B Satellite Clocks: General & Special Relativity Time Variations

    Something that crossed my mind recently; I know that satellites have to adjust their clock due to their relativistic time variations in relation to us. I was wondering do they adjust their times in accordance to general relativity or special relativity or both? Or is their speed so insignificant...
  41. Biker

    I Time Dilation in SR: Exploring Clocks & Perception

    I don't really understand how time dilation works in SR. I just know this that "Now" in one reference frame is not the same in another so for example when Observer A says his time is 10s then at the same moment he will say Observer B's time who is moving relative to him is 5s for example. The...
  42. Sorcerer

    I Understand Twin Paradox, Leading Clocks Lag & Doppler Effect

    I have an obvious understanding failure here, so hopefully someone can help me clear this up. Thanks for reading this obnoxious drivel.Leading clocks lag So, if two clocks are fixed to a the ends of a barn, and they are set off with light pulses from the midpoint, in the frame of the barn the...
  43. S

    I How does the speed of light affect clocks?

    If the speed of light would change in the universe without any other natural constant changing, would all clocks be affected in the same way by this? This is implied by Einstein in this paper on page 368 http://myweb.rz.uni-augsburg.de/~eckern/adp/history/einstein-papers/1912_38_355-369.pdf...
  44. 4

    I Measuring Time with Mirrors: Exploring Special Relativity

    Special relativity is replete with examples of turning mirrors into clocks. Place two mirrors across from one another, bounce light between them, and measure the time. But as I thought about this, when a photon hits the mirror, it is absorbed by an electron which moves to a higher energy...
  45. shahbaznihal

    A Rods, Clocks & Free Fall: Metric & Connections in GR

    In Classical GR the metric tensor ##g_{\mu\nu}## determines the length of rods and ticking of clocks while the connection ##\Gamma^{\alpha}_{\mu\nu}## determine the equation of geodesic (the free fall motion of particle). Furthermore, in GR the Levi-Civita connection is uniquely determined by...
  46. M

    I SR Time Dilation in Rigid Structure Clocks

    Special relativity says that all clocks will show same time dilation, irrespective of clock mechanism. But Time period of a clock is a formula that must continue to hold even if time dilates. Let us look at a tuning fork clock. Here time period depends on the dimensions of the vibrating...
  47. G

    Time Dilation for Moving Rectangle with Clocks at its Corner

    Homework Statement A rectangular structure carries clocks at its four corners. The clocks are synchronized in the structure’s rest frame, in which it has length L =4ft and width W = 3ft. In our laboratory frame the rectangle is moving in the positive x direction at speed v = 0.8c. As the clock...
  48. F

    Synchronized clocks in two moving reference frames

    Homework Statement My professor gave us a werid question which is as follows In the laboratory frame, two clocks are synchronized and measure two light sources at the same time situated at 3 years in time axis and 3 light years and 2 light years in x-axis >At what velocity is the frame ##S'##...
  49. Physics345

    Time Dilation & 2 Atomic Clocks (one in orbit)

    Homework Statement Two atomic clocks are synchronized. One is placed on a satellite, which orbits around the Earth at a high speed for a whole year. The other is placed in a lab and remains at rest, with respect to the earth. You may assume that both clocks can measure time accurately to many...