25. The pressure gradient force acts in a direction
(a) at right angles to the isobars
(b) parallel with the isobars
(C) opposite to the direction of pressure change
Answers
Answer:
Under normal circumstances (i.e. if the Earth were not spinning) air would just move from high to low pressure, across the isobars (due to the Pressure Gradient Force, or PGF). The PGF acts at right angles to the isobars, from high to low pressure. Its size depends on the spacing of the isobars and air density.
However, this is only true around the Equator. In the Northern Hemisphere, air actually moves clockwise round a high pressure area and anticlockwise round a low, because the Earth is spinning, and deflects normal air movement (over the ground), until eventually the wind blows along the isobars (instead of across) at around 2,000 feet. Thus, an imaginary force appears to act at right angles to the rotating Earth, causing a moving body to follow a curved path opposite to the direction of the Earth’s rotation.
Not only that, the Earth moves faster at the equator than it does at the Poles (based on a cosine relationship), so, if you fire an artillery shell from the North Pole to the Equator, progressively more of the Earth's surface would pass under its track, giving the illusion of the object curving to the right (or West of A) as it lags behind - the Earth is moving slower towards the North. If you threw whatever it was the other way, it would “move” to the East of B, because you are adding the Earth’s movement at both latitudes. That is, B will be moving slower relative to A. In other words, a bullet might fly in a straight line, but its target will move to the right.
This apparent movement (East or West) is like extra centrifugal force, which is called in some places the Coriolis Effect, but actually is Geostrophic Force when it refers to air movement, although no “force” is involved, hence the use of the word “effect”. That is, the wind at 2,000 feet is assigned a geostrophic property, which is only true when the isobars are straight and parallel. They are actually mostly curved, so the geostrophic wind becomes the gradient wind. The extra energy to keep the air curving comes from the cyclostrophic force, which is similar to centripetal force, as it operates inward, at 90° to the instantaneous motion, to the right in the Northern Hemisphere and the left in the Southern Hemisphere, until it balances the PGF and the wind follows the isobars. Around a low, it is the difference between PGF and GF - around a high, between GF and PGF.
Explanation:
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Answer:
The correct answer is (a)
Explanation:
The pressure gradient force is perpendicular to an isobar..!