Gravity is typically measured using various instruments and techniques. Here are a few common methods for measuring gravity:
Gravimeters: Gravimeters are specialized instruments designed to measure the acceleration due to gravity at a particular location. They work based on the principle of measuring the displacement of a mass caused by the gravitational force. Different types of gravimeters exist, such as the free-fall gravimeter, which measures the free fall of a test mass in a vacuum, and the spring gravimeter, which measures the displacement of a spring caused by gravity.
Pendulum: The period of a pendulum is affected by the local acceleration due to gravity. By measuring the period of a pendulum, it is possible to infer the gravitational field strength. This method was historically used for gravity measurements and is still employed in certain applications.
Satellite Gravity Measurements: Satellites equipped with sensitive instruments can measure variations in the Earth's gravitational field. These satellites, such as the Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE Follow-On (GRACE-FO), use the technique of satellite-to-satellite tracking or gravitational gradiometry to detect tiny changes in the gravitational field caused by variations in mass distribution.
Absolute and Relative Gravity Measurements: Absolute gravity measurements provide direct values of gravitational acceleration at a specific location. Instruments such as absolute gravimeters are used for this purpose. Relative gravity measurements involve comparing the acceleration due to gravity at different locations. Instruments like relative gravimeters and gravitimeters are employed for relative gravity surveys.
Interferometry: Interferometric techniques, such as atom interferometry or matter-wave interferometry, use the wave-like nature of matter to measure gravity. By measuring the phase shift or interference patterns of matter waves due to gravitational acceleration, precise gravity measurements can be obtained.
It's worth noting that precise gravity measurements are crucial for various applications, including geophysics, geodesy, and studies of Earth's structure, as well as for detecting gravitational anomalies, monitoring changes in groundwater, and studying the dynamics of the Earth's oceans and atmosphere.