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What is a Tidal Force?

A tidal force is the powerful gravitational pull exerted by celestial bodies, like the moon and sun, on one another, causing Earth's oceans to swell and create tides. This cosmic dance affects not just water, but also Earth's crust. Intrigued? Discover how these forces shape our planet and influence life in ways you might never have imagined. Continue reading to explore the depths.
Alan Rankin
Alan Rankin

A tidal force is the effect of an object’s gravitational force on another, nearby object, such as a planet or satellite. This force can influence the object’s shape, orbit, and other characteristics. The most familiar effect of the tidal force is the creation of the high and low tides in the Earth’s oceans. These are created by the gravitational effect of the moon. Other effects are readily observable on the Earth, moon, and other objects in the solar system.

In the 17th century, English scientist Isaac Newton described many of the effects of gravity on the Earth, the moon, and other cosmic bodies. He published his calculations in the groundbreaking treatise Principia Mathematica in 1687. This included a discussion of the tidal force. The word tide refers to the distortion in a body created by another body’s gravity. It is most often used to describe the periodic rise and fall of the Earth’s oceans on its shorelines.

The Moon's gravitational influence on the oceans of the Earth helps create the tides.
The Moon's gravitational influence on the oceans of the Earth helps create the tides.

The tidal force causes a planetary body to bulge slightly in the direction of the outside gravitational force. In the case of the Earth’s shape, this effect is so small as to be hardly noticeable. The water in the oceans, however, is so strongly affected that it surges along the shoreline closest to the moon. This is known as high tide. The water recedes on shores not under this influence, an effect called low tide.

Isaac Newton's "Principia Mathematica" discussed gravity and tidal force.
Isaac Newton's "Principia Mathematica" discussed gravity and tidal force.

Another effect of the moon’s tidal force is to pull the Earth itself slightly away from the oceans on the opposite side of the planet. Consequently, the oceans experience two high tides in a 24-hour period: one when the moon is directly overhead and another 12 hours later, when it is over the opposite side of the globe. When the sun’s weaker gravitational pull combines with that of the moon, more extreme tides, called spring tides, occur. At other times, the sun partially cancels the moon’s tidal force; the resulting weaker tide is known as neap tide.

The word "tide" usually refers to the ocean's rise and fall at a shoreline.
The word "tide" usually refers to the ocean's rise and fall at a shoreline.

The tidal forces have other observable effects. The tidal force of the Earth on the moon results in the same side of the moon always facing the Earth as both bodies rotate in tandem. Objects unable to withstand the stresses of tidal forces can be destroyed by them. This occurred in 1992, when Comet Shoemaker-Levy 9 passed too close to the planet Jupiter. The comet broke into fragments, which then spectacularly collided with the gigantic planet on another pass in 1994.

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    • The Moon's gravitational influence on the oceans of the Earth helps create the tides.
      By: Zhanna Ocheret
      The Moon's gravitational influence on the oceans of the Earth helps create the tides.
    • Isaac Newton's "Principia Mathematica" discussed gravity and tidal force.
      By: Georgios Kollidas
      Isaac Newton's "Principia Mathematica" discussed gravity and tidal force.
    • The word "tide" usually refers to the ocean's rise and fall at a shoreline.
      By: Gabriele Maltinti
      The word "tide" usually refers to the ocean's rise and fall at a shoreline.
    • One effect of the moon's tidal force is to pull the Earth slightly away from the oceans on the opposite side of the planet.
      By: Antony McAulay
      One effect of the moon's tidal force is to pull the Earth slightly away from the oceans on the opposite side of the planet.
    • At times, the sun partially cancels the moon's tidal force, resulting a weaker tide called a neap tide.
      By: pedrol
      At times, the sun partially cancels the moon's tidal force, resulting a weaker tide called a neap tide.
    • Tides are generally less noticeable in the open ocean than along the shoreline.
      By: Galyna Andrushko
      Tides are generally less noticeable in the open ocean than along the shoreline.
    • The tidal force causes a planetary body to to bulge slightly.
      By: Naj
      The tidal force causes a planetary body to to bulge slightly.