Name: why motion seems different in accelerating frames
Uploaded: 2023-04-30T10:54:29.000Z
Duration: 1 min 27 s
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K12 Standards

Pennsylvania State Academic Standards

9-12

Physical Science

Forces and Interactions

3.2.9-12.J

Non-inertial Frames of Reference

Recall that the frames of reference wherein Newton&#39;s laws hold true are known as the inertial frames. However, there are frames of reference which defy Newton&#39;s laws,&#160;called the non-inertial reference frames.
Non-inertial frames are either accelerating or decelerating relative to the inertial frames.
For example, when an airplane takes off, the passengers feel a backward force opposite to the airplane&#39;s acceleration. This violates Newton&#39;s second law according to which objects are accelerated in the direction of the net external force.
In non-inertial frames, inertial or fictitious forces that have no physical origin are necessary to explain the motion of objects. So, in mechanics, it is more convenient to use an inertial frame.
Ideally, a frame of reference fixed to the Earth is non-inertial due to its revolution and rotation. However, the forces due to the Earth&#39;s rotation are negligible in small mechanical motions but affect large-scale motions like wind patterns.
The fictitious force in this frame deflects the wind in the clockwise direction in the northern hemisphere and counterclockwise in the southern hemisphere.

non-inertial frames of reference

A reference frame accelerating or decelerating relative to an inertial frame is a non-inertial frame. To help understand this, consider what taking off in an airplane, turning a corner in a car, riding a merry-go-round, and the circular motion of a tropical cyclone all have in common. All these systems are accelerating, decelerating, or rotating relative to the Earth; hence, they all are non-inertial frames. All these systems exhibit inertial forces, which merely seem to arise from motion, because the observer&#39;s frame of reference is accelerating or rotating. We can reconcile these points of view by examining the frames of reference used. A physicist will choose whatever reference frame is the most convenient for the situation being analyzed. Physicists have no problem in including inertial forces and Newton&#39;s second law, as usual, if that is more convenient. Similarly, non-inertial (accelerated) frames of reference are used when it is helpful. Different frames of reference must be considered, for example, when discussing the motion of an astronaut in a spacecraft traveling at speeds near the speed of light, as this applies to the special theory of relativity.
The Earth can be used as an inertial frame of reference with little or no worry about any effects caused by its rotation. However, such effects do exist, for example, in the rotation of weather systems. Viewed from above the North Pole, the Earth rotates counterclockwise, and any motion in the Earth&#39;s Northern Hemisphere experiences a Coriolis force to the right. The opposite occurs in the Southern Hemisphere, where the force is to the left. Because the Earth&#39;s angular velocity is small, the Coriolis force is usually negligible, but it has substantial effects for large-scale motions, such as wind patterns. The Coriolis force causes hurricanes in the Northern Hemisphere to rotate counterclockwise, whereas tropical cyclones in the Southern Hemisphere rotate clockwise.
The rotation of tropical cyclones and the path of a ball on a merry-go-round can just as well be explained by inertia and the rotation of the system underneath. When non-inertial frames are used, inertial forces, such as the Coriolis force, must be invented to explain the curved path. There is no identifiable physical source for these inertial forces. When inertial frames are used, inertia explains the path, and there is an identifiable source for every force. We can use either view to describe nature, but a view in an inertial frame is simpler, as all forces have origins and explanations.
This text is adapted from <a href="https://openstax.org/books/university-physics-volume-1/pages/5-6-common-forces">Openstax, University Physics Volume 1, Section 5.6: Common Forces</a> and<a href="https://openstax.org/books/university-physics-volume-1/pages/6-3-centripetal-force"> Section 6.3: Centripetal Force.</a>

A reference frame accelerating or decelerating relative to an inertial frame is a non-inertial frame. To help understand this, consider what taking off in ...

Education

JoVE Core

Physics

Unit 1

Newton's Laws of Motion

KEY TERMS AND CONCEPTS

why motion seems different in accelerating frames

A non-inertial frame of reference is a frame that accelerates, decelerates, or rotates relative to an inertial frame. In these frames, motion can look unusual because the observer is moving with the system. That is why an airplane taking off, a car turning a corner, a merry-go-round, and a tropical cyclone can all be examples of non-inertial motion.

These situations can show inertial forces, which seem to appear because the frame itself is accelerating or rotating. The force does not come from a physical source in the usual sense. Instead, it is tied to the observer’s frame of reference.

Physicists choose the reference frame that is most useful for the problem being studied. They can use inertial frames and apply Newton’s second law in the usual way. They can also use non-inertial frames when that makes the description easier.

Different frames of reference matter in special cases, such as an astronaut in a spacecraft moving near the speed of light. This is important in the special theory of relativity. In many problems, the Earth is used as an inertial frame because its rotation causes little trouble.

Even so, Earth’s rotation does affect some motions. Viewed from above the North Pole, Earth rotates counterclockwise. Motion in the Northern Hemisphere then experiences a Coriolis force to the right, while the Southern Hemisphere experiences a force to the left.

Because Earth’s angular velocity is small, the Coriolis force is usually negligible. It still has major effects on large-scale motion, such as wind patterns. It helps explain why hurricanes in the Northern Hemisphere rotate counterclockwise and why tropical cyclones in the Southern Hemisphere rotate clockwise.

The path of a ball on a merry-go-round and the motion of a tropical cyclone can also be explained by inertia and by the rotation of the system underneath. When a non-inertial frame is used, inertial forces such as the Coriolis force must be added to explain the curved path. When an inertial frame is used, inertia explains the motion, and every force has a clear source. Both views can describe nature, but the inertial frame is usually simpler.

Why Motion Seems Different in Accelerating Frames

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key terms and concepts

Explore how accelerating, decelerating, and rotating frames change the way motion looks, from cars and merry-go-rounds to Coriolis force and hurricanes.

Why Motion Seems Different in Accelerating Frames | JoVE K12

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Louisiana Student Standards for Science

High School

motion-and-stability-forces-and-interactions

Motion And Stability: Forces And Interactions

HS-PS2-2

HS-PS2-3

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Forces And Motion

Motion

Tennessee Academic Standards

Motion and Stability: Forces and Interactions

PHYS.PS2.14

Virginia  Standards of Learning

HIgh School

PS.8

PS.8.b

PH.3

PH.3.a

Next Generation Science Standards

Florida Department of Education

SC.912.P.12

SC.912.P.12.3

SC.912.P.12.8

SC.912.P.12.9

Texas Essential Knowledge and Skills

PHYS.5

PHYS.5.C

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Forces and Interactions

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3.2.9-12.M

Why Motion Seems Different in Accelerating Frames

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