Name: free-body diagram for two-block motion
Uploaded: 2025-05-22T09:06:02.000Z
Duration: 1 min 22 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

Steps for Free-Body Diagram

Рассмотрим систему из двух блоков, соединенных безмассовой веревкой над шкивом. Блок 1 скользит по столу, притягиваемому блоком 2, когда он падает под действием силы тяжести. 
Ускорение системы может быть получено путем вычисления результирующей силы, действующей на систему.
Диаграмму свободного тела для этой системы можно нарисовать, представив два блока с их контуром. Здесь блоки считаются изолированными.
Действующие на них внешние силы обозначены и представлены векторными стрелками.
Силы, действующие на блок 1, — это его вес, нормальная сила, сила натяжения от каната и сила трения, противодействующая силе натяжения, вызывающей движение.
Точно так же силы, действующие на блок 2, являются его весом и силой растяжения.
Применяя второй закон движения Ньютона к блокам, можно вывести уравнение для результирующей силы.
Используя алгебраическую операцию и переставляя члены, можно получить величину ускорения системы.

<ol>
	<li>Хиббелер, Р.К. (2016). Инженерная механика \u2012 Статика и динамика. Хобокен, Нью-Джерси: Пирсон Прентис Холл. С. 89</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. 171-172</li>
</ol>

Шаги для создания силовой диаграммы

Когда речь идёт о изучении поведения объектов в механике, одним из самых важных инструментов является силовая диаграмма. Рассмотрим простой пример системы из двух блоков, соединённых безмассовой струной, перекинутой через блок безтрения. Блок 1 скользит по столу, тянуемый блоком 2, который под действием силы тяжести падает.

Чтобы найти ускорение системы, необходимо сначала вычислить суммарную силу, действующую на систему. Для этого можно создать силовую диаграмму, изображающую два блока как единую систему, изолированную от окружающей среды. Затем в диаграмме указываются и представляются векторные стрелки внешних сил.

При рассмотрении блока 1 на него действует несколько сил. Среди них его вес, нормальная сила, сила натяжения, вызванная веревкой, и сила трения, противодействующая силе натяжения и вызывающая движение. В случае блока 2 на него действуют только его вес и силы натяжения.

После создания силовой диаграммы можно применить второй закон Ньютона к блокам. Сделав это, можно получить уравнение для суммарной силы, действующей на систему. В это уравнение войдут массы блоков, ускорение системы и силы, действующие на каждый блок.

Достав уравнение, можно использовать алгебраические операции, чтобы переставить члены и найти величину ускорения системы. Результатом будет числовое значение, представляющее, как система будет вести себя под действием заданных сил.

Важность силовой диаграммы в этой ситуации нельзя переоценить. Она предоставляет ясное и краткое представление о действующих силах, что позволяет более легко и точно рассчитать ускорение системы. Без этого инструмента было бы гораздо сложнее понять и проанализировать поведение блоков и действующие на них силы.

Когда дело доходит до изучения поведения объектов в механике, одним из наиболее важных доступных инструментов является диаграмма свободного тела. Рассмотрим простую ...

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 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 include weight, the normal force, tension from the rope, and friction that opposes the tension force. For block 2, the forces are its weight and the tension force.

After the free-body diagram is complete, Newton’s second law of motion can be applied to the blocks. This gives an equation for the net force on the system. The equation includes the masses of the blocks, the acceleration of the system, and the forces acting on each block.

With the equation set up, algebra can be used to rearrange the terms and solve for the magnitude of the acceleration. The result is a numerical value that describes how the system will move under the given forces. The diagram makes the force analysis clearer and more accurate.

Free-Body Diagram for Two-Block Motion

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 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...

steps for free-body diagram

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 a free-body diagram is used to analyze two blocks connected by a string and pulley, identify forces, and solve for acceleration.

Free-Body Diagram for Two-Block Motion | JoVE K12

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Free-Body Diagram for Two-Block Motion

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