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

K12 Standards

Pennsylvania State Academic Standards

9-12

Physical Science

Forces and Interactions

3.2.9-12.J

Non-inertial Frames of Reference

Ricordiamo che i sistemi di riferimento in cui valgono le leggi di Newton sono noti come sistemi inerziali. Tuttavia, ci sono sistemi di riferimento che sfidano le leggi di Newton, chiamati sistemi di riferimento non inerziali.
I sistemi di riferimento non inerziali stanno accelerando o decelerando rispetto ai sistemi di riferimento inerziali.
Ad esempio, quando un aereo decolla, i passeggeri avvertono una forza all'indietro opposta all'accelerazione dell'aereo. Ciò viola la seconda legge di Newton secondo la quale gli oggetti vengono accelerati nella direzione della forza esterna netta.
Nei sistemi di riferimento non inerziali, forze inerziali o fittizie che non hanno origine fisica sono necessarie per spiegare il movimento degli oggetti. Quindi, in meccanica, è più conveniente utilizzare un telaio inerziale.
Idealmente, un sistema di riferimento fissato alla Terra non è inerziale a causa della sua rivoluzione e rotazione. Tuttavia, le forze dovute alla rotazione terrestre sono trascurabili in piccoli movimenti meccanici, ma influenzano movimenti su larga scala come i modelli di vento.
La forza fittizia in questo sistema di riferimento devia il vento in senso orario nell'emisfero settentrionale e in senso antiorario nell'emisfero meridionale.

Nessun conflitto di interessi dichiarato.

sistemi di riferimento non inerziali

Un sistema di riferimento che accelera o decelera relativamente ad un altro sistema di riferimento è detto non inerziale. Per aiutarti a capire questo, considera ciò che hanno in comune un aereo che decolla, una macchina che curva, il cavalcare una giostra, e il moto circolare di un ciclone tropicale. Tutti questi sistemi accelerano, decelerano, o ruotano relativamente alla Terra; quindi, tutti loro sono sistemi non inerziali. Tutti questi sistemi mostrano forze inerziali, che sembrano derivare dal movimento, perché il sistema di riferimento dell'osservatore sta accelerando o ruotando. Possiamo riconciliare questi punti di vista esaminando il sistema di riferimento usato. Un fisico sceglierà qualunque sistema di riferimento sia il più utile per analizzare la situazione. Se è più conveniente i fisici, come di consueto, non hanno problemi ad includere le forze inerziali e la seconda legge di Newton. Allo stesso modo, i sistemi di riferimento non inerziali (accelerati) vengono usati quando è utile. Devono essere considerati diversi sistemi di riferimento, per esempio, quando discutiamo del movimento di un astronauta in un'astronave che viaggia ad una velocità vicina a quella della luce, poiché ciò si applica in particolare alla teoria della relatività.

La Terra può essere usata come sistema di riferimento inerziale con poche o nessuna preoccupazione riguardo gli effetti causati dalla sua rotazione. Tuttavia, questi effetti esistono, per esempio, nella rotazione dei sistemi meteo. Visto dal Polo Nord, la Terra ruota in senso antiorario, e qualsiasi movimento nell'emisfero Nord della Terra sperimenta la forza di Coriolis a destra. Al contrario nell'Emisfero Sud, la forza è a sinistra. Siccome la velocità angolare della Terra è molto piccola, la forza di Coriolis di solito è trascurabile, ma ha effetti sostanziali per i movimenti su larga scala, come l'andamento del vento. La forza di Coriolis fa si che gli uragani nell'emisfero settentrionale ruotino in senso antiorario, mentre nell'emisfero australe i cicloni tropicali ruotano in senso orario.

La rotazione dei cicloni tropicali e il percorso di una palla su una giostra possono essere entrambi spiegati dall'inerzia della rotazione del sistema sottostante. Quando si usano sistemi son inerziali, le forze inerziali, come quella di Coriolis, devono essere concepite per spiegare il percorso curvo. Non esiste nessuna causa fisica identificabile per queste forze inerziali. Quando si usano sistemi inerziali, l'inerzia spiega il percorso, e c'è una fonte identificabile per ogni forza. Possiamo usare entrambi i punti di vista per descrivere la natura, ma la visione del sistema inerziale è più semplice, poiché tutte le forze hanno un'origine e una spiegazione.

Questo testo è adattato da <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> e <a href="https://openstax.org/books/university-physics-volume-1/pages/6-3-centripetal-force">Section 6.3: Centripetal Force.</a>

Sistemi di riferimento non inerziali

Un sistema di riferimento che accelera o decelera rispetto a un sistema di riferimento inerziale è un sistema di riferimento non inerziale. Per aiutare a capire questo, considera cosa decollare in ...

Education

Didattica

JoVE Core

Physics

Fisica

Unit 1

Unità 1

Newton's Laws of Motion

Le leggi del moto di Newton

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

why-motion-seems-different-in-accelerating-frames

force

Understanding Force in Motion

Force is a push or pull that acts on an object. It has both magnitude and direction, so force is a vector quantity. In everyday life, force appears when we open a door, walk down a street, lift a fork, or touch a baby's face. Forces also shape matter at the smallest scales. The atoms in our bodies are held together by electrical forces. The nucleus of an atom is held together by nuclear force, which is the strongest force known to us. The study of motion is called kinematics. Kinematics...

types of forces

Contact and Field Forces in Physics

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newton's first law: introduction

Newton's First Law and Inertia

Newton's first law of motion explains inertia and how forces change motion. Motion can be striking to observe, from a dolphin jumping from water to a bird in flight or a satellite moving in orbit. The study of motion is kinematics, which describes velocity and acceleration. Dynamics goes further by examining the forces that affect moving objects and systems. Newton's laws of motion are the foundation of dynamics. They are simple in form, but they describe a wide range of natural behavior.

newton's first law: application

Newton's First Law and Friction

Newton's first law explains why friction changes an object's motion. It says that an object at rest stays at rest, and an object in motion keeps moving unless a net external force acts on it. A net external force is the overall force from outside the object that causes a change in velocity, meaning a change in speed or direction. This idea gives a cause-and-effect reason for motion, rather than just describing what we see. Galileo first developed the idea behind the first law of motion, and...

internal and external forces

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External forces and motion changes are linked in Newton’s first law. A net external force causes a change in motion. External forces act on an object or system from outside that object or system. Internal forces come from inside the system of interest. They act on one part of an object and are exerted by another part of the same object. These forces do not cause acceleration when the whole system is studied. When analyzing motion, the internal forces are ignored. Instead, only the external...

newton's second law

Force, Mass, and Acceleration

Newton's second law connects net force, mass, and acceleration. It explains how an object's motion changes when external forces act on it. The law gives a clear cause-and-effect link that can be used to make calculations. All external forces on a system are added together to find the net force, or F net. A larger net external force produces a larger acceleration. The acceleration points in the same direction as the net force. Mass also affects the result. A larger mass means more inertia, so...

mass and weight

Weight Changes, Mass Stays Constant

Mass and weight are related, but they are not the same. In physics, weight is the pull of the Earth on an object. It depends on how far the object is from the center of the Earth. Mass is the amount of matter in an object, and it does not change with location. Everyday language can make this difference confusing. Medical records often list body weight in kilograms, even though the correct force unit is the newton. That can make mass and weight seem interchangeable. In physics, however, they...

weightlessness

Weightlessness in Free Fall

Weightlessness happens when contact forces disappear, even though gravity is still present. In physics, an object in free fall has only gravity acting on it. If the net external force on the object is its weight, the object is accelerating toward the center of the Earth. Galileo showed that, without air resistance, all objects fall with the same acceleration g. On Earth, falling objects are never truly in free fall because air always pushes upward with some resistance force. That is why real...

apparent weight

Scale Readings in Motion and Water

Scale readings can change when an object is moving or submerged in water. The force we call true weight is the gravitational force acting on an object. When motion or fluid forces are present, the reading can differ from that true weight. In water, this changed reading is called apparent weight, and it equals true weight minus the buoyant force. A bathroom scale in an elevator shows how this works. At rest, the scale reads the force the person pushes downward on it. The only forces on the...

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newton's third law: introduction

Newton's Third Law in Force Pairs

Newton's third law explains how force pairs work in motion and interactions. When one body exerts a force on a second body, the first body experiences a force that is equal in magnitude and opposite in direction. A simple example is a person pushing on a wall. The wall pushes back on the person with an equal and opposite force. This is why Newton's third law is often described as action and reaction, where the action is the force exerted and the reaction is the force experienced afterward. <br...

newton's third law: examples

Newton's Third Law in Motion

Newton's third law explains how forces come in pairs during motion. It says that every action has an equal and opposite reaction. In these examples, the two forces act on different systems, so they do not cancel each other out. A swimmer pushing off the side of a pool shows this clearly. The swimmer pushes against the wall with their feet and then accelerates in the opposite direction. The wall pushes back with an equal and opposite force. If the swimmer is the system of interest, the wall's...

drawing free-body diagrams: rules

Free-Body Diagrams for Newton’s Laws

Free-body diagrams help students map the forces acting on an object in physics. They are used often when studying and applying Newton’s laws of motion. A clear diagram makes it easier to analyze a system before solving for motion. Start by drawing the object under consideration. If the object is treated like a particle, show it as a point and place that point at the origin of an x-y coordinate system. Then add every force that acts on the object as a vector. Do not include the net force on the...

free body diagrams: examples

Free Body Diagram Force Examples

Free body diagrams show the external forces acting on an object or system. The object is drawn as a single isolated point, or free body, so the forces are easier to analyze. Only forces that come from outside the object or system are included. These forces are shown as vectors pointing away from the free body. A person sitting on a chair is a simple example. The free-body diagram has two forces. The chair exerts an upward normal force, and gravity pulls downward with the weight. A rocket sled...

inertial frames of reference

Newton's First Law and Reference Frames

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non-inertial frames of reference

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...

centrifugal force

Rotating Frames and Pseudo Forces

Pseudo forces, also called fictitious forces, appear in a rotating frame of reference when compared with an inertial frame. They are not real forces. Instead, they are mathematical tools that help make Newton&amp;#39;s laws of motion easier to use in a non-inertial frame. Common examples include centrifugal, Coriolis, and Euler forces. These forces matter in mechanics, astrophysics, and fluid dynamics. In these areas, motion is often described from a frame that is not inertial. That is why...

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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

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

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

HS-PS2-1.

Newton's Second Law

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Second Law: Motion under Same Force

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Second Law: Motion under Same Acceleration

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Students who demonstrate understanding can analyze data to support the claim that Newton's second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.  Clarifying Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.  Assessment Boundry: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.

3.2.9-12.I

Inertial Frames of Reference

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Linear Momentum

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Conservation of Momentum: Problem Solving

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Students who demonstrate understanding can use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.  Clarifying Statement: Emphasis is on the quantitative conservation of momentum in interactions and the qualitative meaning of this principle.  Assessment Boundry: Assessment is limited to systems of two macroscopic bodies moving in one dimension.

Students who demonstrate understanding can apply scientific and engineering ideas to design, evaluate and refine a device that minimizes the force on a macroscopic object during a collision. Clarifying Statement: Examples of evaluation and refinement could include determining the success of the device at protecting an object from damage and modifying the design to improve it. Examples of a device could include a football helmet or a parachute. Assessment Boundry: Assessment is limited to qualitative evaluations and/or algebraic manipulations.

3.2.9-12.K

Gravitation

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Newton's Law of Gravitation

Our everyday observation tells us that all objects close to the Earth naturally tend to fall to the ground. Early philosophers assumed that this downward ...

Electric Charges

From lightning during thunderstorms to electronic devices, the phenomenon of electromagnetism is all around us. The electromagnetic force is one of the ...

sources-and-properties-of-electric-charge

Sources and Properties of Electric Charge

All objects we see around us consist of atoms, which combine to form molecules. The lightest element in the universe is hydrogen, and a hydrogen atom ...

Coulomb's Law

Experiments with electric charges have shown that if two objects each have an electric charge, they exert an electric force on each other. The magnitude ...

the-principle-of-superposition-and-the-gravitational-field

The Principle of Superposition and the Gravitational Field

The principle of superposition applies to gravitational forces of objects that are sufficiently far apart. It states that the net gravitational force on a ...

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Electric Field

Consider two point charges, each exerting Coulomb force on the other. It is possible to describe the Coulomb interaction via an intermediate step by ...

Magnetic Fields

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Magnetic Field due to Moving Charges

A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a ...

Electromagnetic Fields

Electric fields generated by static charges, often referred to as electrostatic fields, are characteristically different from electric fields created by ...

Students who demonstrate understanding can use mathematical representations of Newton's Law of Gravitation and Coulomb's Law to describe and predict the gravitational and electrostatic forces between objects. Clarifying Statement: Emphasis is on both quantitative and conceptual descriptions of gravitational and electric fields. Assessment Boundry: Assessment is limited to systems with two objects.

3.2.9-12.L

Energy Transfer in Chemical Reactions

Chemical reactions require sufficient energy to cause the matter to collide with enough precision and force that old chemical bonds can be broken and new ...

Batteries and Fuel Cells

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Students who demonstrate understanding can plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current. Clarifying Statement: N/A Assessment Boundry: Assessment is limited to designing and conducting investigations with provided materials and tools.

3.2.9-12.M

Why Motion Seems Different in Accelerating Frames

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