Name: free-body diagrams for force analysis
Uploaded: 2023-09-22T11:49:20.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

HS-PS2-3

Free-body Diagram

Визуальное представление всех сил, действующих на частицу, называется диаграммой свободного тела или диаграммой силы. Он преобразует сложные задачи в простые представления.
На диаграмме произвольного тела направление стрелок указывает направление сил, а длина стрелок представляет величину сил.
Рассмотрим стационарную тележку, на которой уложены две картонные коробки.
Здесь две интересующие нас системы, бокс 1 и бокс два, могут быть приняты как изолированные системы и могут быть представлены с помощью диаграммы свободного тела в виде простого контура или точки.
Силы, действующие на бокс 1, — это гравитационная сила, определяющая его вес, и уравновешивающая нормальная сила, возникающая из-за бокса два.
Точно так же силы на коробке номер два — это ее собственный вес, нормальная сила, возникающая при движении тележки, и масса коробки номер один.
Диаграммы свободного тела играют неотъемлемую роль в процессе решения проблемы как переход от конкретной физической ситуации к абстрактному математическому уравнению в механике.

<ol>
	<li>Хиббелер, Р.К. (2016). Инженерная механика \u2012 Статика и динамика. Хобокен, Нью-Джерси: Пирсон Прентис Холл. С. 88</li>
	<li>Бир, Ф..; Джонстон, Э.Р.; Мазурек, Д.Ф; Кромвель,.Д. и Селф, Б.. (2019). Векторная механика для инженеров \u2012 Статика и динамика. Нью-Йорк: Макгроу-Хилл. С. 170-171</li>
</ol>

Схема свободного тела

В механике понимание движения объектов является важным, и одним из инструментов, помогающих решить эту проблему, является схема свободного тела. Это простое, но мощное графическое представление, кратко описывающее все силы, действующие на объект. Схема свободного тела может представлять неподвижный или движущийся объект, и используется в механике для объяснения причины движения объекта.

Схема свободного тела превращает сложную проблему в простое представление, что делает понимание основных сил, действующих на объект, и приводит к математическому уравнению, лёгким. Во многих случаях уравнение было бы крайне сложно получить без использования схем свободного тела. Чтобы создать схему свободного тела, начните с выбора объекта или системы для исследования, изолируя его от окружающей среды, и изобразите его точкой или простой контур. Затем изобразите все основные внешние силы, действующие на объект или систему интереса, стрелками. Направление стрелок представляет направление силы, а длина стрелок отображает величину силы. Важно отметить, что на схеме свободного тела скорость и ускорение не представлены, но могут быть выведены из сил, действующих на объект.

Некоторые общие типы сил, которые могут быть представлены на схеме свободного тела, включают вес, нормальную силу, натяжение, трение и приложенную силу. Под весом понимается сила тяжести, действующая на объект, обычно представленная стрелкой, указывающей вниз. Нормальная сила - это сила между двумя объектами, когда они соприкасаются друг с другом; эта сила действует в противоположном направлении по отношению к весу объекта. Натяжение, как правило, представлено стрелкой, указывающей от объекта в направлении силы, а трение - это сила, сопротивляющаяся скольжению между поверхностями. Наконец, приложенная сила относится к силе, приложенной к объекту внешним агентом, таким как толчок или потягивание. Приложенные силы представлены стрелкой, указывающей в направлении силы.

Рассмотрим неподвижную тележку, на которой установлены две картонные коробки. Две системы интереса, коробка один и коробка два, можно считать изолированными системами и можно представить с помощью схемы свободного тела. Силы, действующие на коробку один, это сила тяжести, определяющая её вес, и силы равновесия - это нормальная сила, обусловленная коробкой два. Аналогично, на коробку два действуют её вес, нормальная сила, вызванная тележкой, и вес коробки один.

В механике понимание движения объектов имеет важное значение, и одним из инструментов, помогающих решить эту проблему, является диаграмма свободного тела. Это простой, но ...

Education

JoVE Core

Mechanical Engineering

Машиностроение

Unit 1

Раздел 1

Equilibrium of a Particle

Равновесие частицы

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

free-body diagrams for force analysis

Free-body diagrams help analyze the forces acting on an object in mechanics. They give a simple picture of a stationary or moving object and show why it moves the way it does. By turning a complex situation into a clear sketch, they make it easier to write the equation needed to solve the problem.

To draw a free-body diagram, first choose the object or system you want to study. Then isolate it from its surroundings and draw it as a dot or a simple outline. Add arrows for every important external force. The direction of each arrow shows the direction of the force, and the length shows its size.

A free-body diagram does not show velocity or acceleration. Those quantities are not drawn on the diagram, but they can be inferred from the forces acting on the object. Common forces include weight, normal force, tension, friction, and applied force. Weight is the force of gravity and is usually shown with an arrow pointing downward.

Normal force is the contact force between two objects touching each other. It acts in the direction opposite to the object's weight in many situations. Tension is usually drawn as an arrow away from the object and along the direction of the pull. Friction resists sliding between surfaces. Applied force is an outside push or pull, and it is shown with an arrow in the direction of that force.

A stationary trolley with two cardboard boxes stacked on it gives a clear example. Box one and box two can each be treated as separate isolated systems and shown with their own free-body diagrams. For box one, the forces are gravitational force and the balancing normal force from box two. For box two, the forces are its weight, the normal force from the trolley, and the weight of box one.

Free-Body Diagrams for Force Analysis

equilibrium conditions for a particle

Balanced Forces and Torque in Equilibrium

Equilibrium depends on balanced forces and balanced torque. An object in equilibrium is either at rest or moving with a constant velocity. These two cases are called static equilibrium and dynamic equilibrium. Static equilibrium means the object is not moving. Dynamic equilibrium means the object is moving, but its velocity stays constant. In both cases, the forces acting on the object must balance each other. Different forces can add, subtract, or cancel each other out. When the vector sum...

free-body diagram

Free-body diagrams help analyze the forces acting on an object in mechanics. They give a simple picture of a stationary or moving object and show why it moves the way it does. By turning a complex situation into a clear sketch, they make it easier to write the equation needed to solve the problem. To draw a free-body diagram, first choose the object or system you want to study. Then isolate it from its surroundings and draw it as a dot or a simple outline. Add arrows for every important...

steps for free-body diagram

Free-Body Diagram for Two-Block Motion

A free-body diagram helps analyze two-block motion in mechanics. It shows the forces acting on a system so the net force can be found and the acceleration can be calculated. The example in this lesson uses two blocks linked by a massless string over a frictionless pulley. Block 1 moves across a table while block 2 falls under gravity. The two blocks are treated as one isolated system. External forces are then identified and drawn as vector arrows on the diagram. For block 1, the forces...

free-body diagrams: problem solving

Free-Body Diagrams on Inclined Planes

Free-body diagrams help show the forces acting on an object on an inclined plane. A free-body diagram is a simple drawing that focuses only on the object or system being studied. It leaves out extra details so the force problem is easier to analyze and solve. For an example, a 10 kg block is released on a ramp that is 30° to the horizontal. The coefficient of friction is 0.2. The diagram for this block includes the weight from gravity, the normal force, and the frictional force. These are the...

coplanar forces

Resolving Coplanar Force Components

Coplanar forces act on an object in the same plane. To analyze this kind of system, each force is resolved into x and y components using Cartesian vector form and vector algebra. This makes it possible to test whether the object is in equilibrium. A coplanar system is in equilibrium when the resultant force is zero. That means the sum of the forces in each direction must also be zero. If the forces do not balance, the object is not in equilibrium and will accelerate in the direction of the net...

categories of equilibrium

Types of Equilibrium in Forces

Equilibrium in physics describes how forces act on a body so it stays still or moves at a constant speed. In two-dimensional force systems, equilibrium can be grouped into several categories based on how the forces are arranged. Collinear equilibrium is the simplest case. The forces act along one straight line, so only one force equation is needed in the direction of those forces. The other equations are already satisfied. Coplanar concurrent equilibrium is another category. In this case, all...

key terms and concepts

Learn how free-body diagrams show weight, normal force, tension, friction, and applied force. See how isolating an object simplifies force analysis in mechanics.

Free-Body Diagrams for Force Analysis | JoVE K12

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HS-PS2-6

Free-Body Diagrams for Force Analysis

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