Name: tire deformation and rolling resistance
Uploaded: 2023-09-22T11:49:30.000Z
Duration: 1 min 21 s
Channel: JoVE

K12 Standards

Arizona Science Standards

High School

Physical Science

HS.P3

HS.P3U2.7

Rolling Resistance

Considere um pneu rolando a uma velocidade constante. As forças que atuam sobre ele são seu peso e a força normal.
As superfícies de contato se deformam, criando uma área de contato finita. Isso resulta em uma distribuição de forças normais em cada ponto de contato.
A seção frontal desta área sofre deformação, o que retarda o movimento de rolamento.
Em contraste, a seção traseira passa por uma restauração relativamente menor que empurra o pneu para frente.
A força normal resultante atuando em A é a soma dessas forças.
Para manter o pneu rolando a uma velocidade constante e equilibrar o momento do peso em torno de A, uma força motriz horizontal deve ser aplicada ao centro do pneu. Aqui todas as forças devem ser concorrentes.
A condição de equilíbrio de momento no ponto A fornece a força motriz em termos do coeficiente de resistência ao rolamento.
O peso multiplicado pelo coeficiente de resistência ao rolamento sobre o raio é geralmente menor que o coeficiente de atrito cinético vezes o peso.
Assim, a força de atrito de rolamento é menor que a força de deslizamento.

<ol>
	<li>Hibbeler, R.C. (2016). Engenharia Mecânica \u2012 Estática e Dinâmica. Hoboken, Nova Jersey: Pearson Prentice Hall. pág. 452 \u2012 439.</li>
	<li>Oliveira, J.L.; Kraige, L.G. e Bolton, J.N. (2020). Engenharia Mecânica \u2012 Estática. Hoboken, Nova Jersey: John Wiley. pág. 372.</li>
	<li>Cerveja, F.P.; Johnston, E.R.; Mazurek, D.F; Cromwell, PJ e Self, BP (2019). Mecânica vetorial para engenheiros \u2012 estática e dinâmica. Nova Iorque: McGraw-Hill. pág. 469.</li>
</ol>

resistência ao rolamento

Quando um cilindro sólido rola de maneira constante em uma superfície rígida, a força normal aplicada pela superfície no cilindro é perpendicular à tangente no ponto de contato. No entanto, como nenhum material é totalmente rígido, a reação da superfície ao cilindro envolve uma variedade de pressões normais.

Por exemplo, imagine um cilindro duro rolando em uma superfície relativamente macia. O peso do cilindro comprime a superfície abaixo dele. Conforme o cilindro se move, o material na frente dele desacelera devido à deformação, enquanto o material atrás dele se recupera de seu estado deformado, empurrando o cilindro para frente. As pressões normais atuando no cilindro dessa maneira são representadas por suas forças resultantes, Nd e Nr. A força de deformação (Nd) e seu componente horizontal são consistentemente maiores que a força de restauração (Nr), exigindo a aplicação de uma força horizontal no cilindro para manter seu movimento.

A resistência ao rolamento ocorre principalmente devido a esse efeito, embora também seja influenciada, em menor grau, pela aderência à superfície e pelo microdeslizamento relativo entre as superfícies de contato.

Para explicar melhor esse conceito, considere um pneu rolando a uma velocidade constante. As principais forças atuando nele são seu peso, atuando verticalmente para baixo, e a força normal exercida pelo solo, atuando verticalmente para cima. Conforme o pneu rola, a seção frontal da área de contato sofre deformação, o que retarda o movimento de rolamento do pneu. Em contraste, a seção traseira passa por uma restauração relativamente menor que impulsiona o pneu para frente. O efeito líquido é que a força normal resultante atuando no ponto A (o centro da área de contato) é a soma dessas forças opostas.

<img alt="Figure 1" src="/files/ftp_upload/14328/14328_Figure_1v2.svg" style="text-align: center; height: 350px;" />

Para manter o pneu rolando a uma velocidade constante e equilibrar o momento do peso em relação ao ponto A, uma força horizontal F deve ser aplicada ao centro do pneu. Para o equilíbrio, todas as forças atuando no pneu devem ser concorrentes. Usando a condição de equilíbrio de momento no ponto A, podemos determinar a força de condução necessária para manter a velocidade constante em termos do coeficiente de resistência ao rolamento (a).

<img alt="Equation 1" src="/files/ftp_upload/14328/14328_Equation_1v2.svg" style="text-align: center; height: 28px;" />

Essa força de condução geralmente é menor que o produto do coeficiente de atrito cinético e do peso do pneu.

<img alt="Equation 2" src="/files/ftp_upload/14328/14328_Equation_2v2.svg" style="text-align: center; height: 28px;" />

Essa relação implica que a força de atrito de rolamento é tipicamente menor que a força de deslizamento experimentada quando um pneu derrapa sobre uma superfície. Como resultado, a resistência ao rolamento é geralmente menos prejudicial ao desempenho de um veículo do que o atrito de deslizamento.

Resistência ao Rolamento

Quando um cilindro sólido rola firmemente sobre uma superfície rígida, a força normal aplicada pela superfície no cilindro é perpendicular à tangente no ...

Education

JoVE Core

Mechanical Engineering

Engenharia Mecânica

Unit 1

Unidade 1

Friction

Atrito

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

tire deformation and rolling resistance

Tire deformation and rolling resistance explain why a rolling wheel still needs a driving force. When a solid cylinder or tire rolls on a rigid surface, the normal force is perpendicular to the surface at the contact point. But real materials are not perfectly rigid, so the surface pushes back with a spread of normal pressures instead of one single force.

A hard cylinder on a softer surface compresses the material under it. As the cylinder moves forward, the material in front of the contact area slows because it is being deformed. The material behind the cylinder begins to recover, and that recovery pushes the cylinder forward.

These effects are often shown as two resultants, N d for the deformation force and N r for the restoration force. The deformation force and its horizontal component are larger than the restoration force. Because of that imbalance, a horizontal driving force must be applied to keep the cylinder moving.

The same idea applies to a tire rolling at constant speed. Its weight acts downward, and the ground provides an upward normal force. The front of the contact patch deforms and slows the tire, while the rear part restores more weakly and pushes it forward. The resultant normal force at point A is the sum of these opposing effects.

To keep the tire in equilibrium and maintain constant speed, a horizontal driving force F must act at the center of the tire. Using moment equilibrium about point A, the needed driving force can be written in terms of the rolling resistance coefficient a. This force is usually smaller than the force from kinetic friction, so rolling resistance is less harmful than sliding when a tire skids.

Rolling resistance is mainly caused by surface deformation, but adhesion and small-scale sliding between surfaces can also play a smaller role. These effects help explain why rolling wheels still lose some energy even when they do not appear to slip.

Tire Deformation and Rolling Resistance

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Tire deformation and rolling resistance explain why a rolling wheel still needs a driving force. When a solid cylinder or tire rolls on a rigid surface, the normal force is perpendicular to the surface at the contact point. But real materials are not perfectly rigid, so the surface pushes back with a spread of normal pressures instead of one single force. A hard cylinder on a softer surface compresses the material under it. As the cylinder moves forward, the material in front of the contact...

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key terms and concepts

Learn how tire deformation creates rolling resistance, why a driving force is needed, and how it compares with sliding friction in moving wheels.

Tire Deformation and Rolling Resistance | 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.

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Tire Deformation and Rolling Resistance

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