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

A eficiência mecânica de uma máquina é a relação entre a produção e o trabalho de entrada.
Para uma máquina ideal, a proporção é um, o que implica que o trabalho de entrada e saída são iguais.
Por exemplo, em uma morsa basculante ideal que comprime madeira, o trabalho de saída devido à força de reação é igual ao trabalho de entrada devido à força aplicada.
Em contraste, uma máquina real experimenta força de atrito.
A força de atrito pode ser obtida a partir da força de reação normal.
O trabalho virtual total devido às forças contribuintes, quando aplicado no princípio do trabalho virtual, dá o trabalho de saída como a diferença entre o trabalho de entrada e o trabalho devido à força de atrito.
Dividir o trabalho de saída pelo trabalho de entrada dá a eficiência mecânica. A eficiência na ausência de atrito é uma delas. No entanto, para um coeficiente de atrito diferente de zero, a eficiência é zero quando o ângulo de alternância é igual ao ângulo de atrito e negativo para ângulos de alternância menores que o ângulo de atrito.
Isso implica que um torno deve ser usado apenas para um ângulo de alternância maior que o ângulo de atrito.

<ol>
	<li>Cerveja, F.P., Johnston, E.R., Mazurek, D.F., Cornwell, P.J. e Self, B.P. (2016). Mecânica vetorial para engenheiros. Décima primeira edição, Nova York: McGraw-Hill Education. Pág. 580-581.</li>
</ol>

eficiência mecânica de máquinas reais

A eficiência mecânica de uma máquina é um conceito fundamental que descreve quão efetivamente uma máquina pode converter o trabalho de entrada em trabalho de saída. De acordo com esse conceito, a eficiência de uma máquina é igual à razão entre o trabalho de saída e o trabalho de entrada. Uma máquina ideal, ou seja, uma máquina que não possui perdas de energia, possui uma eficiência de um. Isso implica que o trabalho de entrada e o trabalho de saída são iguais.

No entanto, na realidade, nenhuma máquina pode ser verdadeiramente ideal e todas elas sofrem algum tipo de perda de energia. Uma das principais fontes de perda de energia em máquinas é o atrito. Por exemplo, considere um torno usado para comprimir blocos de madeira. Na ausência de atrito, o trabalho de saída do torno é igual ao trabalho de entrada da força aplicada, tornando-o uma máquina ideal.

No entanto, na realidade, o bloco deslizante do torno sofre uma força de atrito contra o plano horizontal. Para determinar a eficiência mecânica de um torno real, primeiro calcule a reação normal e a força de atrito correspondente. Em seguida, avalie o trabalho virtual total de todas as forças durante o deslocamento virtual. Aplicando o princípio do trabalho virtual, o trabalho de saída do torno é a diferença entre o trabalho de entrada e o trabalho da força de atrito.

Consequentemente, a força de reação líquida pode ser calculada, sendo zero quando o ângulo do torno é igual ao ângulo de atrito e negativo quando é menor que o ângulo de atrito. Isso significa que o torno deve ser usado apenas quando seu ângulo excede o ângulo de atrito.



A eficiência mecânica do torno na ausência de atrito é igual a um. No entanto, quando o atrito está presente, a eficiência pode se tornar zero ou menor que um, dependendo do coeficiente de atrito. Quanto menor o coeficiente de atrito, mais próxima a eficiência estará de um - inversamente, quanto maior o coeficiente de atrito, menor será a eficiência.

A eficiência mecânica de uma máquina é um conceito essencial que explica quão efetivamente uma máquina pode converter o trabalho de entrada em trabalho de saída. Na realidade, nenhuma máquina pode ser totalmente ideal e todas elas sofrem algum tipo de perda de energia devido a atrito. Ao analisar a eficiência de uma máquina, é crucial considerar os efeitos do atrito e seu coeficiente, pois eles desempenham um papel significativo na determinação da força de reação líquida e da eficiência geral da máquina. Embora uma máquina ideal possa alcançar uma eficiência perfeita, máquinas reais sempre terão eficiência inferior à ideal devido a perdas de energia, especialmente por atrito.

Eficiência Mecânica de Máquinas Reais

A eficiência mecânica de uma máquina é um conceito fundamental que descreve a eficácia com que uma máquina pode converter o trabalho de entrada em trabalho de saída. ...

Education

JoVE Core

Mechanical Engineering

Engenharia Mecânica

Unit 1

Unidade 1

Virtual Work

Trabalho Virtual

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

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mechanical efficiency of real machines

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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

O JoVE Core Mechanical Engineering oferece vídeos animados concisos e de fácil compreensão que abrangem tópicos-chave como equilíbrio, forças, análise de treliças e mecânica estrutural. Explore suas aplicações no mundo real e observe esses conceitos em ação por meio de experimentos conduzidos por cientistas.

mechanical engineering

Friction’s Role in Machine Efficiency

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