Everything about The Tidal Force totally explained
The
tidal force is a secondary effect of the
force of
gravity and is responsible for the
tides. It arises because the gravitational acceleration experienced by a large body isn't constant across its
diameter. One side of the body has greater
acceleration than its
center of mass, and the other side of the body has lesser acceleration.
Explanation
When a body (body 1) is acted on by the gravity of another body (body 2), the field can vary significantly on body 1 between the side of the body facing body 2 and the side facing away from body 2. This causes strains on both bodies and may distort them or even, in extreme cases, break one or the other apart. These strains wouldn't occur if the gravitational field is uniform, since a uniform
field only causes the entire body to accelerate together in the same direction and at the same rate.
The figure shows
Comet Shoemaker-Levy 9 after it had broken up under the influence of Jupiter's tidal forces. The comet was falling into Jupiter, and the parts of the comet closest to Jupiter fell with a greater acceleration, due to the greater gravitational force. From the point of view of an observer riding on the comet, it would appear that the parts in front split off in the forward direction, while the parts in back split off in the backward direction. In reality, however, all parts of the comet were accelerating toward
Jupiter, but at different rates.
Effects of tidal forces
In the case of an elastic sphere, the effect of a tidal force is to distort the shape of the body without any change in volume. The sphere becomes an
ellipsoid, with two bulges, pointing towards and away from the other body. This is essentially what happens to the Earth's oceans. Although the Earth isn't falling along a line directly toward the moon, the Earth is continuously accelerating due to the moon's gravitational forces, causing it to wobble around their common
center of mass. All parts of the Earth accelerate in response to the moon's gravitational forces, but to an observer on the Earth, it appears that the Earth's center remains at rest, while water in the oceans is redistributed to form bulges on the sides near the moon and far from the moon.
When a body rotates while subject to tidal forces, internal friction results in the gradual dissipation of its rotational kinetic energy as heat. If the body is close enough to its primary, this can result in a rotation which is tidally locked to the orbital motion, as in the case of the Earth's moon. Tidal heating produces dramatic volcanic effects on Jupiter's moon
Io.
Tidal forces contribute to ocean currents, which moderate global temperatures by transporting heat energy toward the poles. It has been suggested that in addition to variations of
insolation associated with
orbital forcing,
harmonic beat variations in tidal forcing may contribute to climate changes.
Tidal effects become particularly pronounced near small bodies of high mass, such as
neutron stars or
black holes, where they're responsible for the "
spaghettification" of infalling matter. Tidal forces create the oceanic
tide of
Earth's oceans, where the attracting bodies are the
Moon and the
Sun.
Tidal forces are also responsible for
tidal locking and
tidal acceleration.
Mathematical treatment
For a given (externally generated) gravitational field, the
tidal acceleration at a point with respect to a body is obtained by
vectorially subtracting the gravitational acceleration at the center of the body from the actual gravitational acceleration at the point. Correspondingly, the term
tidal force is used to describe the forces due to tidal acceleration. Note that for these purposes the only gravitational field considered is the external one; the gravitational field of the body (as shown in the graphic) isn't relevant.
for a more exact version ]]
Tidal acceleration doesn't require rotation or orbiting bodies; for example the body may be
freefalling in a straight line under the influence of a gravitational field while still being influenced by (changing) tidal acceleration.
Newton's law of universal gravitation states that a particle of mass
m a distance
r from the center of a sphere of mass
M feels a force of:
»
The tidal forces can also be calculated away from the axis connecting the bodies, requiring a
vector calculation of forces. In the plane perpendicular to the axis, the tidal force is directed inwards, and its magnitude is
in linear approximation as above .
Further Information
Get more info on 'Tidal Force'.
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