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Related Concept Videos

Physical Pendulum01:06

Physical Pendulum

When a rigid body is hanging freely from a fixed pivot point and is displaced, it oscillates similar to a simple pendulum and is known as a physical pendulum. The period and angular frequency of a physical pendulum are obtained by using the small-angle approximation and drawing parallels with a spring-mass system. The small-angle approximation (sinθ=θ) is valid up to about 14°.
When dealing with complicated systems, the mass moment of inertia is an important parameter, as it describes the mass...
Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession, and the angular frequency...
Faraday Disk Dynamo01:23

Faraday Disk Dynamo

A Faraday disk dynamo is a DC generator, producing an emf that is constant in time. It consists of a conducting disk that rotates with a constant angular velocity in the magnetic field, perpendicular to the disk's plane. The rotation of the disk causes a change in magnetic flux, which induces an emf, causing opposite charges to develop on the rim and in the center of the disk. The polarity of the induced emf can be determined by the direction of the magnetic field and the direction of the...
Simple Pendulum01:10

Simple Pendulum

A simple pendulum consists of a small diameter ball suspended from a string, which has negligible mass but is strong enough to not stretch. In our daily life, pendulums have many uses, such as in clocks, on a swing set, and on a sinker on a fishing line.
The period of a simple pendulum depends on two factors: its length and the acceleration due to gravity. The period is completely independent of any other factors, such as mass or maximum displacement. For small displacements, a pendulum is...
Applications of RC Circuits01:22

Applications of RC Circuits

A relaxation oscillator is one of the applications of RC circuits. A neon lamp relaxation oscillator comprises a capacitor, a resistor, a voltage source, and a lamp. The lamp acts like an open circuit, with infinite resistance until the potential difference across the lamp reaches a specific voltage. At that voltage, the lamp acts like a short circuit with zero resistance, and the capacitor discharges through the lamp, thus producing light. Once the capacitor is fully discharged through the...
Oscillations In An LC Circuit01:31

Oscillations In An LC Circuit

An idealized LC circuit of zero resistance can oscillate without any source of emf by shifting the energy stored in the circuit between the electric and magnetic fields. In such an LC circuit, if the capacitor contains a charge q before the switch is closed, then all the energy of the circuit is initially stored in the electric field of the capacitor. This energy is given by

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Related Experiment Video

Updated: Jul 12, 2026

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh
10:42

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Published on: May 3, 2019

Millisecond Pulsar PSR 1937+21: A Highly Stable Clock.

L A Rawley, J H Taylor, M M Davis

    Science (New York, N.Y.)
    |November 6, 1987
    PubMed
    Summary

    PSR 1937+21, a pulsar, demonstrates remarkable frequency stability, rivaling atomic clocks. This research provides a new upper limit for cosmic gravitational radiation energy density.

    Area of Science:

    • Astronomy
    • Astrophysics
    • Pulsar Astronomy

    Background:

    • Pulsars, like PSR 1937+21, exhibit stable rotation and sharp radio pulses.
    • These characteristics allow pulsars to function as highly precise cosmic clocks.
    • Atomic clocks represent the current standard for long-term frequency stability.

    Purpose of the Study:

    • To assess the long-term frequency stability of the pulsar PSR 1937+21.
    • To compare the pulsar's stability against state-of-the-art atomic clocks.
    • To establish an upper limit for the energy density of a cosmic background of gravitational radiation.

    Main Methods:

    • Utilizing the Arecibo radio telescope for precise measurements of pulse arrival times.
    • Employing advanced measurement techniques to achieve uncertainties of approximately 300 nanoseconds relative to atomic time.

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  • Conducting bi-weekly measurements since November 1982 to analyze long-term stability trends.

    • Main Results:

    • PSR 1937+21 exhibits fractional frequency stability of at least 6 x 10(-14) for averaging times exceeding 4 months.
    • Measurement precision appears limited by the stability of reference atomic clocks over extended intervals.
    • A firm upper limit of 7 x 10(-36) g/cm³ was determined for the energy density of gravitational radiation at 0.23 cycles per year.

    Conclusions:

    • The pulsar PSR 1937+21 serves as a highly stable clock, potentially surpassing atomic clocks.
    • The study provides crucial constraints on the density of cosmic gravitational radiation.
    • The derived limit for gravitational radiation is approximately 4 x 10(-7) of the density required to close the universe.