Name: forces inside a body and balance
Uploaded: 2023-09-22T11:49:22.000Z
Duration: 1 min 25 s
Channel: JoVE

内部力は、粒子間の相互作用により、体内で生成されます。これらの力には、引張、圧縮、せん断が含まれます。 
内力は、同じ大きさで方向が反対の同一線上のペアに存在します。それらは接続されたすべての部分間で相殺され、体の平衡状態になります。
物体の重量は、物体の重心を介して作用する単一の合力によって表される外力です。
これは、外力が体に作用しない限り、体がそれ自体のバランスをとるポイントです。
対称または均一な物体は、その幾何学的中心に重心があります。ただし、不規則な体や不均一な体の場合、重い側に向かって中心がずれています。
クレーンの中央にビームが取り付けられ、その端に荷重が接続されているとします。片側の荷重が重くなると、重心がビームの中心線から離れ、転倒する可能性があります。
安定性を確保するために重心を特定する必要があり、リフティングフックはその真上に配置する必要があります。

<ol>
	<li>ラッセルC.ヒベラー。(2016). エンジニアリングメカニクス:静力学とダイナミクス。ピアソン。212ページ。</li>
</ol>

内力と重心

Internal Forces and Center of Gravity

内力と重心は力学における基本的な概念であり、さまざまな状況下で構造物や物体の振る舞いや安定性を理解するために重要な役割を果たしています。これらの原理を包括的に理解することは、安全で効率的なシステムを作り出すために、エンジニアや建築家、設計者にとって不可欠です。

内力は、物体内部の粒子間の相互作用によって発生します。これらの力は、引張力、圧縮力、せん断力の3つに分類することができます。これらの内力は同じ大きさで逆方向を持つ対合するペアとして存在し、すべての接続部分で互いに打ち消し合い、物体の平衡を維持します。

物体の重量は、物体の重心を通る単一の合力で表される外力です。重心とは、外力が作用しない状態で物体が自己平衡をとる点です。重心は対称的または均等な物体では幾何学的な中心に位置しますが、不規則または非均一な物体ではより重い側にオフセットされる場合があります。

内力と重心の理解は、さまざまな構造物や物体の安定性と平衡を分析し維持するために重要です。たとえば、土木工学では、これらの原理を使用して風や地震、交通負荷などの外力に耐える橋や建物、その他のインフラストラクチャを設計します。

機械工学では、内力と重心の知識を活用して、さまざまな負荷や条件下で安全かつ効率的に動作する機械、車両、その他の機械システムを設計します。

航空宇宙工学では、航空機や宇宙船の重心を正確に決定することが飛行中の安定性と制御を確保するために重要です。重心の移動は、これらの乗り物の性能と安全性に重大な影響を与えることがあります。

内力と重心は力学の基本的な概念であり、力学の振る舞いと安定性を理解する上で重要な役割を果たします...

Education

JoVE Core

Mechanical Engineering

機械工学

Unit 1

ユニット1

Equilibrium of a Rigid Body

剛体のつり合い

KEY TERMS AND CONCEPTS

主要用語と概念

forces inside a body and balance

Internal forces and the center of gravity help explain how objects stay in balance. These mechanics ideas matter for structures, machines, and vehicles that must remain stable under different loads and conditions.

Internal forces are created inside a body when its particles interact. They can appear as tension, compression, or shear forces. These forces act in collinear pairs with equal magnitude and opposite direction. Between connected parts, they cancel each other and help keep the body in equilibrium.

A body’s weight is an external force. It is shown as one resultant force acting through the center of gravity. The center of gravity is the point where a body balances when no external force acts on it. For symmetrical or uniform bodies, this point is at the geometric center. For irregular or non-uniform bodies, it may shift toward the heavier side.

These ideas are important in civil engineering, mechanical engineering, and aerospace engineering. Engineers use them to design bridges, buildings, machines, vehicles, aircraft, and spacecraft that can handle wind, earthquakes, traffic loads, and other forces. If the center of gravity changes, the stability and safety of an aircraft or spacecraft can be affected.

Forces Inside a Body and Balance

conditions of equilibrium

Rigid Body Force Balance in Equilibrium

Rigid body equilibrium depends on a balance of external forces and moments. A rigid body is in equilibrium when it has no translational motion and no rotational motion. This happens when the net force and the net couple acting on the body are both zero. Internal forces are not used when checking equilibrium. These forces act in equal and opposite pairs inside the body, so they cancel each other. Because of that, they do not affect the overall motion or change in motion of the rigid body. The...

support reactions

Types of Structural Supports

Types of structural supports control how a coplanar force system moves and reacts under load. A coplanar force system is a set of forces that all lie in the same plane. The supports create reactions at the point of contact. These reactions help keep a structure stable under external forces. Supports work by stopping translation with an equal and opposite force. They can also stop rotation by applying a couple moment in the opposite direction. In structural design, these reactions are important...

internal forces and center of gravity

Internal forces and the center of gravity help explain how objects stay in balance. These mechanics ideas matter for structures, machines, and vehicles that must remain stable under different loads and conditions. Internal forces are created inside a body when its particles interact. They can appear as tension, compression, or shear forces. These forces act in collinear pairs with equal magnitude and opposite direction. Between connected parts, they cancel each other and help keep the body in...

alternative sets of equilibrium equations

alternative-sets-of-equilibrium-equations

Equilibrium Conditions for a Supported Plate

Equilibrium conditions for a supported plate are used to describe when forces and moments balance. In this state, the plate has no net movement and no rotation. Engineers use these equations to study how structures behave under external loads. In many cases, the standard equilibrium equations are enough. But some systems need an alternative set of equations to match the geometry of the support points. A rectangular plate supported at points A, B, and C is one example. For this plate, the...

two force member

Two-Force Body Equilibrium

A two-force body is a rigid body acted on by only two external forces. In equilibrium, those two forces must have the same magnitude, the same line of action, and opposite directions. This balance is what keeps the body at rest. For a plate with forces F1 and F2 applied at points A and B, equilibrium means the sum of moments about any axis is zero. If moments are summed about point A, the moment from F2 must be zero. That means the line of action of F2 must pass through point A. The same idea...

three force member

Solving a Three-Force Member Example

A three-force member is a rigid body acted on by three forces at three points. The forces must have concurrent lines of action. If the forces are parallel, their lines of action stay parallel instead. A dumpster provides the example used here. It is connected to a pin support at point A and to a pin on a hydraulic cylinder at point B. The hydraulic cylinder acts as a two-force member in equilibrium. The dumpster weight acts through the center of gravity, and the support reaction acts at point...

equations of equilibrium in three dimensions

equations-of-equilibrium-in-three-dimensions

Checking Force Balance in 3D Structures

Checking force balance in 3D structures is a key step when a system is at rest. The vector and scalar equations of equilibrium are used to test whether a body is stable and will not collapse or fall apart. These equations give a clear way to study the forces acting on a body. The vector equations of equilibrium require the vector sum of all external forces on a body to equal zero. They also require the vector sum of the couple moments and the moments of all forces about a point to equal zero.

support reactions in three dimensions

3D Support Types for Stability and Motion

Support reactions in three dimensions keep structures stable and in equilibrium. They stop unwanted translation and rotation, so a design can handle external forces safely and work as intended. These reactions are important in many structures and systems. A ball and socket joint is one support that allows free rotation about any axis. It does not provide a moment that resists turning. At the same time, it restricts motion in space with three reaction forces along the three dimensions. A...

constraints and statical determinacy

Constraints in Structural Equilibrium

Constraints in structural engineering control how a body can move and help keep it in mechanical equilibrium. A constraint is a restriction on motion. When the right number of constraints is used, the system can stay balanced with the fewest supports needed. A system with the proper number of supports is called statically determinate. In that case, the unknown reaction forces can be found from equations of equilibrium. These systems are the easiest to analyze and design because the forces can...

key terms and concepts

Learn how internal forces and the center of gravity affect balance, stability, and equilibrium in structures, machines, and vehicles.

Forces Inside a Body and Balance | JoVE K12

JoVE Core 機械工学は、平衡、力、トラス解析、構造力学などの重要なトピックをカバーする簡潔でわかりやすいアニメーション ビデオを提供します。実際のアプリケーションを探索し、科学者主導の実験を通じてこれらのコンセプトが実際に動作しているのを目撃してください。

mechanical engineering

Forces Inside a Body and Balance

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