NATS 101 Lecture 16 Newton’s Laws of Motion Upper-Air Winds

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NATS 101 Lecture 16 Newton’s Laws of Motion Upper-Air Winds. Supplemental References for Today’s Lecture. Gedzelman, S. D., 1980: The Science and Wonders of the Atmosphere . 535 pp. John-Wiley &amp; Sons. (ISBN 0-471-02972-6). PGF. Wind. Do Rocks Always Roll Downhill?. PGF. Upper-Level Winds.

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### NATS 101Lecture 16Newton’s Laws of MotionUpper-Air Winds

Supplemental References for Today’s Lecture

Gedzelman, S. D., 1980: The Science and Wonders of the Atmosphere. 535 pp. John-Wiley & Sons. (ISBN 0-471-02972-6)

PGF

Wind

Do Rocks Always Roll Downhill?

PGF

Upper-Level Winds

Gedzelman, p 247

Newton’s Laws of Motion
• Newton’s 1st Law

An object at rest will remain at rest and an object in motion will remain at a constant velocity (same speed and same direction) if the net force exerted on it is zero

An external force is required to speed up, slow down, or change the direction of air

Newton’s Laws of Motion
• Newton’s 2nd Law

The net force exerted on an object equals its mass times its acceleration

Sum of All Forces = Mass  Acceleration

Acceleration = Velocity Change / Time

Acceleration = Change in Either Speed or Direction

New Velocity

New Velocity

Acceleration and Force

Acceleration and Force

Original Velocity

Original Velocity

New Velocity

Original Velocity

Original Velocity

New Velocity

Velocity, Acceleration and Force are Vectors
• Size and Direction

New Velocity

Acceleration directed toward center of circle Centripetal

Original Velocity

Uniform, Circular Motion Requires Acceleration

Circular Path

New Velocity

Original Velocity

Accelerated Frame of Reference

You are glued to car’s floor and drop an egg.

What happens if the car begins to accelerate?

Inside the car, it looks a mystery force is attracting the egg to the back of the car.Your frame of reference is accelerating.

(rest)

Someone outside the car sees that the egg is just accelerating to the floor, you are accelerating with the box car. A force is accelerating the car. Their frame of referenceis not accelerating.

time

Splat!

Life on a Rotating Platform
• From perspective of person not on merry-go-round, path of ball is straight.
• From perspective of person on merry-go-round, path of ball deflects to left. There is anapparent force.

(left click picture for animation) World Weather Project 2010 Courtesy of M. Ramamurthy U of Illinois, Urbana-Champaign

Earth’s Rotation

Gedzelman, p 240

If viewed from space, earth is like a carousel!

Northern Hemisphere rotates counterclockwise

Southern Hemisphere rotates clockwise

Ball Appears to Deflect to the Right of the Observer

Deflection increases if: Rotation rate increases Speed of ball increases

Gedzelman, p 242

Apparent Deflection

No Deflection

velocity

Gedzelman, p 242

• Parcel at rest initially accelerates toward lower pressure.
• Coriolis Force rotates parcel to right in NH.
• As parcel speeds up, Coriolis Force increases.
• Eventually (about a day), PGF equals CF and flow is parallel to isobars.

World Weather Project 2010 Courtesy of M. Ramamurthy U of Illinois, Urbana-Champaign

Animate Picture

5640 m

Geostrophic Wind

5700 m

Coriolis Force

Geostrophic Balance

Geostrophic Wind Arises from a Balance Between the PGF and the Coriolis Force.

PGF + Coriolis Force = 0

Technically, can exist only for East-West flow and for straight contours.

5640 m

Geostrophic Wind

5700 m

Coriolis Force

Geostrophic Balance

The Balance Leads to the Wind Blowing Parallel to the Height Contours, with Lower Heights to the Left of the Wind Direction in the NH.

Closer the Spacing Between the Height Contours- The Faster the Geostrophic Wind Speed.

PGF

Cor

Geo

Key Concepts for Today
• Rotation of Earth

Accelerated Frame of Reference

• Introduce Coriolis “Force”

Apparent Force to Account for Deflection Depends on Rotation, Latitude, Wind Speed

• Geostrophic Balance and Wind

Balance Between PGF and Coriolis Force Geostrophic Wind Blows Parallel to Contours About One Day Required to Reach Balance

Assignment for Next Lecture
• Topic –Centripetal force due to curved flow

Frictional force near the ground