Name: rotating frames and pseudo forces
Uploaded: 2023-05-16T08:18:40.000Z
Duration: 1 min 6 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Physics

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

PHYS.PS2.14

Centrifugal Force

Vous êtes-vous déjà demandé pourquoi une balle vole vers l’extérieur dans un manège rotatif ?
Lorsque le manège tourne, la balle trace une trajectoire circulaire. La composante de la force de tension dans la corde fournit la force centripète nécessaire au mouvement circulaire de la balle.
La force centripète est dirigée vers le centre du cercle et est désignée par le produit de la masse de l'objet, du carré de sa vitesse angulaire et de sa distance par rapport à l'axe de rotation.
Puisque la balle vole vers l'extérieur, il s'ensuit de la troisième loi de Newton que la force centripète vers l'intérieur doit avoir une force de réaction vers l'extérieur égale et opposée. Cette force vers l’extérieur dirigée à l’opposé du centre de rotation est appelée force centrifuge.
La balle en rotation dans le manège subit une force centrifuge qui la pousse vers l’extérieur en s’éloignant du centre de rotation.
La force centrifuge est une pseudo-force. Il n’est envisagé que lorsque le cadre d’observation est non inertiel.

<ol>
	<li>Giancoli, D.C (2014). Principes de physique avec applications. San Francisco, Californie : Pearson. Annexe C.</li>
	<li>OpenStax. (2019). Physique universitaire Vol. 1. [Version Web] pp.298. Récupéré de <a href="https://openstax.org/books/university-physics-volume-1/pages/6-3-centripetal-force">https://openstax.org/books/university-physics-volume-1/pages/6-3-centripetal-force</a></li>
</ol>

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force centrifuge

Les pseudoforces, ou forces fictives, semblent agir sur un objet en mouvement dans un référentiel en rotation par rapport à un référentiel inertiel. Ces forces ne sont pas réelles, mais plutôt des constructions mathématiques, introduites pour simplifier les calculs dans un référentiel non inertiel tout en utilisant les lois du mouvement de Newton. Des exemples courants de pseudoforces incluent les forces centrifuges, Coriolis et Euler. Ces forces sont essentielles dans des domaines tels que la mécanique, l'astrophysique et la dynamique des fluides, où le mouvement d'objets dans des référentiels non inertiels est couramment rencontré.

Considérons une balle attachée à une corde tournoyant dans un plan horizontal. Selon la première loi du mouvement de Newton, observée à partir d'un référentiel inertiel, la balle se déplacerait en ligne droite. Cependant, la tension dans la corde fournit en continu la force centripète nécessaire pour maintenir la balle en mouvement sur une trajectoire circulaire. La force centrifuge n'est pas requise dans ce référentiel inertiel, car tout mouvement peut être adéquatement décrit en utilisant uniquement des forces réelles et les lois du mouvement de Newton.

Maintenant, considérons un référentiel en rotation avec la balle autour du même axe que la balle. Vu de ce référentiel, la balle est immobile. Cependant, la force de tension dans la corde ou la force centripète agit toujours sur la balle dirigée vers l'axe de rotation.

Cela contredit les lois du mouvement de Newton, selon lesquelles la balle doit accélérer dans la direction de la force appliquée nette, c'est-à-dire vers l'axe de rotation. L'introduction d'une force centrifuge égale et opposée à la force centripète résout le problème. La force nette sur la balle est nulle, ce qui la maintient immobile dans le référentiel en rotation.

Les forces fictives sont nécessaires pour formuler les équations de mouvement correctes en utilisant les deux premières lois de Newton. Cependant, les forces fictives ne respectent pas la troisième loi de Newton, qui exige que les forces égales et opposées existent dans le même référentiel. Cela signifie que les forces centrifuges et centripètes ne sont pas des forces d'action et de réaction.

Force centrifuge

Les pseudo-forces, ou forces fictives, semblent agir sur un objet en mouvement dans un référentiel en rotation par rapport à un référentiel inertiel. ...

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Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Newton's Laws of Motion

Les lois du mouvement de Newton

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 pseudo forces are useful when analyzing rotating systems and other moving reference frames.

A simple example is a ball tied to a string and whirled in a horizontal circle. From an inertial frame, the ball would move in a straight line if the string were not pulling on it. The tension in the string provides the centripetal force, which keeps the ball moving in a circular path. In this frame, centrifugal force is not needed because the motion can be explained using real forces and Newton&amp;#39;s laws.

Now look at the same ball from a frame rotating with it around the same axis. In that rotating frame, the ball appears stationary. The tension still acts toward the axis of rotation, which would seem to conflict with Newton&amp;#39;s laws. Adding a centrifugal force equal in size and opposite in direction to the centripetal force makes the net force zero and keeps the ball at rest in the rotating frame.

Fictitious forces are therefore needed to write correct equations of motion with Newton&amp;#39;s first two laws in non-inertial frames. They do not obey Newton&amp;#39;s third law. That means centrifugal and centripetal forces are not an action-reaction pair, because the equal and opposite forces must be in the same frame of reference.

Rotating Frames and Pseudo Forces

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

Forces in physics are often grouped as contact forces and field forces. Contact forces happen when objects touch directly. Field forces act without direct physical contact. They come from a field, which is a region of space that can be detected by the force it exerts on a body. Scientists describe four fundamental force fields in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear. The gravitational field gives a body its weight. The electromagnetic field includes static...

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

External Forces and Motion Changes

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

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...

centrifugal force

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...

key terms and concepts

Explore pseudo forces in rotating frames, including centrifugal force, centripetal force, and why a spinning ball stays at rest in the rotating frame.

Rotating Frames and Pseudo Forces | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

Virginia  Standards of Learning

HIgh School

Physical Science

PS.8

PS.8.b

PH.3

PH.3.a

Arizona Science Standards

HS+Phy.P3

HS+Phy.P3U1.3

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Forces and Interactions

HS-PS2-1.

Electric Charges

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Describe and mathematically determine the electrostatic interaction between electrically charged particles using Coulomb’s law. Compare and contrast Coulomb’s law and gravitational force, notably with respect to distance. Describe and mathematically determine the electrostatic interaction between electrically charged particles using Coulomb’s law. Compare and contrast Coulomb’s law and gravitational force, notably with respect to distance. EXPLANATION: Comparisons should note that both of these forces decrease proportional to the square of the distance and both are field interactions. Due to the nature of electric charge, it is possible that coulombic forces can be either attractive or repulsive depending on the charges, while gravitational forces are attractive. Descriptions of electrostatic fields should also include field line diagrams representing both strength and direction of the field in space.

PHYS.PS2.10

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work-energy-theorem-for-motion-along-a-curve

Work-Energy Theorem for Motion Along a Curve

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Frictional Force

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Static and Kinetic Frictional Force

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Develop and apply the impulsemomentum theorem along with scientific and engineering ideas to evaluate and refine a device that minimizes the force on an object during a collision. Develop and apply the impulsemomentum theorem along with scientific and engineering ideas to evaluate and refine a device that minimizes the force on an object during a collision. EXPLANATION: This topic can be related to conservation of energy and workenergy theorem to explore that bringing an object to rest requires a set amount of energy to be dissipated. By increasing the stopping distance of the object during the time when the force is applied, the required force is decreased since the total work done on the stopping object remains constant. Students can design systems to maximize the stopping distance and in turn decrease the force required to stop the object. Working with constraints on their designs provides students an opportunity to make design decisions in applying their scientific knowledge.

PHYS.PS2.11

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Apparent Weight

True weight is the measure of the gravitational force acting on an object. However, if the object accelerates, its measured weight is different from its ...

Drag Force and Terminal Speed

An interesting force in everyday life is the force of drag on an object when it is moving in a fluid. Like friction, the drag force always opposes the ...

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Use experimental evidence to demonstrate that air resistance is a velocity dependent drag force that leads to terminal velocity. Use experimental evidence to demonstrate that air resistance is a velocity dependent drag force that leads to terminal velocity.      EXPLANATION:  In performing such an experiment, students should treat air resistance as the dependent variable and must therefore be able to manipulate this variable. This can be done by considering a force diagram for an object falling at its terminal velocity. (PHYS.PS2.5) Doing so will reveal that the drag force is equal to the weight force. By varying the weight, the drag force is also varied. If an object with a significant air resistance is used, the terminal velocity can be determined when dropping the object from a significant height. (Note: A common misconception is to treat drag force and weight force as a third law pair. This is incorrect.)

PHYS.PS2.12

Drawing Free-body Diagrams: Rules

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Free Body Diagrams: Examples

Solving problems that involve forces is easy using free-body diagrams. A free-body diagram is a sketch showing all the external forces that are acting on ...

Projectile Motion

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Projectile Motion: Equations

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Projectile Motion: Example

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PHYS.PS2.13

principle-linear-impulse-momentum-for-single-particle-problem

Principle of Linear Impulse and Momentum for a Single Particle: Problem Solving

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Non-uniform Circular Motion

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Dynamics Of Circular Motion: Applications

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Inertial Frames of Reference

Newton&#8217;s first law is usually considered to be a statement about reference frames. It provides a method for identifying a special type of reference ...

Non-inertial Frames of Reference

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Plan and conduct an investigation to provide evidence that a constant force perpendicular to an object’s motion is required for uniform circular motion (F = mV^2/r).  Plan and conduct an investigation to provide evidence that a constant force perpendicular to an object’s motion is required for uniform circular motion (F = mV^2/r).  EXPLANATION:  Circular motion requires a balance of two factors: a velocity which will carry an object forward and a force perpendicular to the object’s velocity. This perpendicular force will cause the object’s trajectory to curve inwards in the direction of the force, while continuing to travel forward.  Building on a student’s understanding of projectile motion, it should be made evident that the object’s velocity will not change as there is no component to the force parallel to the object’s motion. Investigations can be performed by selecting variables which students hypothesize will have an effect on the motion of an object moving in a circular pattern. If force sensors are available, this lab can be done by measuring the centrally directed force. Without force sensors, students can perform their investigation using a loose string passing through the center of a hollow tube. A measured hanging mass on the loose end of the string can be used to determine the tension force when the uniform circular motion is achieved. Discussions should also include circular paths that may not be complete circles, such as the apex of a hill or a curve in the road.  (It is essential to clearly distinguish between uniform circular motion and rotational motion.)

Rotating Frames and Pseudo Forces

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