Name: friction’s role in machine efficiency
Uploaded: 2023-09-22T11:49:20.000Z
Duration: 1 min 14 s
Channel: JoVE

기계의 기계적 효율성은 입력 작업에 대한 출력 작업의 비율입니다.
이상적인 기계의 경우 비율이 1이며, 이는 입력 및 출력 작업이 동일함을 의미합니다.
예를 들어, 나무를 압축하는 이상적인 토글 바이스에서 반력으로 인한 출력 작업은 적용된 힘으로 인한 입력 작업과 같습니다.
대조적으로, 실제 기계는 마찰력을 경험합니다.
마찰력은 수직 반력에서 얻을 수 있습니다.
기여하는 힘으로 인한 총 가상 작업은 가상 작업의 원칙에 적용될 때 마찰력으로 인한 작업과 입력 작업의 차이로 출력 작업을 제공합니다.
출력 작업을 입력 작업으로 나누면 기계적 효율성이 향상됩니다. 마찰이 없을 때의 효율성은 하나입니다. 그러나 마찰 계수가 0이 아닌 경우 토글 각도가 마찰 각도와 같을 때 효율성은 0이고 토글 각도가 마찰 각도보다 작으면 음수입니다.
이는 바이스가 마찰 각도보다 큰 토글 각도에만 사용되어야 함을 의미합니다.

<ol>
	<li>Beer, F.P., Johnston, E.R., Mazurek, D.F., Cornwell, P.J. 및 Self, B.P. (2016). 엔지니어를 위한 벡터 역학. 제 11 판, 뉴욕 : McGraw-Hill Education. 580-581쪽.</li>
</ol>

실제기계의 기계적 효율성에 관한 연구

기계의 기계적 효율은 기계가 입력된 일을 얼마나 효과적으로 출력된 일로 변환할 수 있는지를 설명하는 기본 개념입니다. 이 개념에 따르면 기계의 효율은 투입된 일에 대한 출력된 일의 비율과 같습니다. 이상적인 기계는 에너지 손실이 없는 기계를 의미하며 효율이 1입니다. 이는 입력된 일과 출력된 일이 같다는 것을 의미합니다.
그러나 실제로 어떤 기계도 완벽할 수 없으며 모든 기계는 어떤 형태로든 에너지 손실을 경험합니다. 기계에서 에너지 손실의 주요 원인 중 하나는 마찰입니다. 예를 들어 나무 블록을 압축하는 데 사용되는 토글 바이스를 생각해 보세요. 마찰이 없을 때 바이스의 출력 작업은 가해진 힘의 입력 작업과 같으므로 이상적인 기계입니다. 
하지만 실제로는 바이스의 슬라이딩 블록이 수평면에 대해 마찰력을 경험합니다. 실제 바이스의 역학적 효율을 결정하기 위해서는 먼저 정상적인 반응과 상응하는 마찰력을 계산해야 합니다. 그런 다음 가상 변위 동안 모든 힘의 총 가상 일을 평가합니다. 가상 일의 원리를 적용하면 바이스의 출력 일은 입력 일과 마찰력 일의 차이로 나옵니다. 
따라서 바이스의 각도가 마찰각과 같을 때는 0, 마찰각보다 작을 때는 음수인 순반력을 계산할 수 있습니다. 이는 바이스의 각도가 마찰각을 초과할 때만 사용해야 한다는 것을 의미합니다.
마찰이 없을 때 바이스의 기계적 효율은 1입니다. 그러나 마찰이 있을 때 효율은 마찰계수에 따라 0이 될 수도 있고 1보다 작을 수도 있습니다. 마찰계수가 낮을수록 효율은 1에 가까울 것입니다. 반대로 마찰계수가 높을수록 효율은 떨어집니다.
기계의 기계적 효율은 기계가 입력된 일을 출력된 일로 얼마나 효과적으로 변환할 수 있는지를 설명하는 중요한 개념입니다. 현실에서 어떤 기계도 완전히 이상적일 수 없으며, 그들은 모두 마찰로 인해 어떤 형태로든 에너지 손실을 경험합니다. 기계의 효율을 분석할 때 마찰의 영향과 계수를 고려하는 것은 기계의 순반력과 전체 효율을 결정하는 데 중요한 역할을 하기 때문입니다. 이상적인 기계는 완벽한 효율을 얻을 수 있지만, 실제 기계는 특히 마찰로 인한 에너지 손실로 인해 항상 이상적인 효율보다 적을 것입니다.

기계의 기계적 효율성은 기계가 입력 작업을 출력 작업으로 얼마나 효과적으로 변환할 수 있는지를 설명하는 기본 개념입니다. ...

Education

교육

JoVE Core

Mechanical Engineering

기계공학

Unit 1

제1단원

Virtual Work

가상일

KEY TERMS AND CONCEPTS

주요 용어 및 개념

Mechanical Efficiency of Real Machines

friction’s role in machine efficiency

Mechanical efficiency shows how well a machine turns input work into output work. It is calculated as the ratio of output work to input work. An ideal machine has an efficiency of one, which means the input work equals the output work.

Real machines are never perfectly ideal because some energy is lost. Friction is one of the main causes of that loss. In a toggle vise used to compress wooden blocks, the sliding block rubs against the horizontal plane and creates friction.

To find the efficiency of a real vise, first calculate the normal reaction and the frictional force. Then use the principle of virtual work to evaluate the total virtual work of all the forces during a virtual displacement. With friction present, the output work equals the input work minus the work done by friction.

This analysis also gives the net reaction force. It is zero when the angle of the vise equals the angle of friction. It becomes negative when the angle is smaller than the angle of friction, so the vise should be used only when its angle is greater than the friction angle.

A vise with no friction has an efficiency of one. When friction is present, the efficiency can be less than one or even zero, depending on the coefficient of friction. A lower coefficient of friction gives an efficiency closer to one, while a higher coefficient lowers the efficiency.

Friction’s Role in Machine Efficiency

work

Work in Force and Motion

Work connects force, motion, and energy in mechanics. It happens when a force acts on an object and the object moves along the line of action of that force. Work can also be described as energy transfer caused by applying a force, which leads to a change in the object’s motion or position. Work is calculated as the force multiplied by the part of the displacement in the same direction as the force. It can also be written as the dot product of the applied force and the object’s displacement. In...

work of a couple moment

Couple Moment Work in Rotation

Mechanical engineering studies motion, energy, and force, and it uses the idea of a couple moment to describe how two equal and opposite forces act on a rigid body. A couple moment is created when those forces act at two points on the body that are separated by a distance. When a rigid body moves because of a couple, its displacement can be split into two parts. First, the two points move by the same amount to their final positions. Then the body rotates about one of those points. During the...

virtual work

Virtual Work in Force Equilibrium

Virtual work is a mechanics principle used to check equilibrium with imaginary motion. If a body is in static or dynamic equilibrium, the total virtual work from external forces and couple moments must be zero for any virtual displacement. A virtual displacement is an imagined small movement. It can be a shift or a rotation. The virtual work done by a force equals the force dotted with the virtual displacement in the force’s direction. For a couple moment, virtual rotational work is found by...

virtual work for a system of connected rigid bodies

virtual-work-for-a-system-of-connected-rigid-bodies

Finding Forces with Virtual Work in Linked Bodies

Virtual work helps find forces in a system of connected rigid bodies. It is a useful method when several links move together and the system is in equilibrium. In that case, the total virtual work is zero. To analyze the system, start with a free-body diagram. Use one independent coordinate to describe the link configuration. Then mark the deflected position that comes from a positive virtual displacement. This makes the small change in position clear before any calculations begin. Next,...

principle of virtual work: problem solving

principle-of-virtual-work-problem-solving

Virtual Work for Finding Unknown Forces

The principle of virtual work helps find unknown forces and moments in equilibrium problems. It is an important idea in mechanics and engineering. The method uses a small, hypothetical motion called a virtual displacement. If the system is in equilibrium, the work done by the forces during that displacement is zero. To apply this principle, the positions of the internal and external forces must be written in terms of one common coordinate parameter. That parameter can be an angle, a distance,...

mechanical efficiency of real machines

Mechanical efficiency shows how well a machine turns input work into output work. It is calculated as the ratio of output work to input work. An ideal machine has an efficiency of one, which means the input work equals the output work. Real machines are never perfectly ideal because some energy is lost. Friction is one of the main causes of that loss. In a toggle vise used to compress wooden blocks, the sliding block rubs against the horizontal plane and creates friction. To find the...

conservative forces

Conservative Forces and Path-Independent Work

Conservative forces are forces whose work depends only on an object’s starting and ending positions. The path between those positions does not change the amount of work done. This idea is important in mechanical engineering because it helps describe how energy moves through a system. A conservative force also conserves energy in the sense that its work is path independent. Gravity is one example. Electrostatic forces and springs modeled by Hooke’s law are also examples. A ball rolling down a...

potential energy

Gravitational and Elastic Energy Stored

Gravitational and elastic potential energy are forms of stored energy from conservative forces. A conservative force, such as gravity or an elastic force, gives a body the capacity to do work. This capacity is measured as potential energy and depends on the body’s position relative to a fixed reference point, or datum. For gravitational potential energy, the datum is the level where the energy is taken as zero. If a body is above this reference plane, its weight has positive gravitational...

potential-energy criterion for equilibrium

potential-energy-criterion-for-equilibrium

Stable Equilibrium Through Potential Energy

Potential energy helps determine when a mechanical system is stable at equilibrium. When a system is acted on by gravitational and elastic forces, its total potential function is the algebraic sum of gravitational potential energy and elastic potential energy. If the system is already in equilibrium and is given a small displacement, the work done on the system equals the negative of the change in potential energy between the starting and ending positions. For a virtual displacement, which is...

stability of equilibrium configuration

Types of Equilibrium in Mechanical Systems

Types of equilibrium in mechanical systems are stable, neutral, and unstable. These three cases help explain how a structure or object responds when it is pushed slightly away from balance. They are important for predicting whether a system will return to its original position, stay where it is, or move farther away. Stable equilibrium occurs when a system returns toward its original position after a small displacement. In this case, the potential energy is at a minimum. A cantilever beam...

one-degree-of-freedom system

Spring-Mass Motion and Energy Stability

A one-degree-of-freedom system uses a single independent variable to describe its state and behavior. In mechanical engineering, this kind of model helps explain how parts in a larger system respond to force. It also gives engineers a way to predict motion before a design is built in real life. A simple harmonic oscillator is one example of a one-degree-of-freedom system. A mass attached to a spring moves along one axis, and that position determines the system’s state. The spring force makes...

stability of equilibrium configuration: problem solving

stability-of-equilibrium-configuration-problem-solving

Equilibrium Stability Through Potential Energy

Stability of equilibrium in physics and engineering can be studied by using a system’s potential energy. An equilibrium configuration is a state where the system can remain at rest. Stability describes whether the system tends to return to that state after a small disturbance. Problem solving begins by finding the equilibrium points of the system. This is done by setting the derivative of the potential energy function equal to zero and solving for the independent variable values that satisfy...

key terms and concepts

Learn how friction lowers mechanical efficiency in real machines, using a toggle vise example, virtual work, and the angle of friction.

Friction’s Role in Machine Efficiency | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

Friction’s Role in Machine Efficiency

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