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

Considera uno pneumatico che rotola a velocità costante. Le forze che agiscono su di esso sono il suo peso e la forza normale.
Le superfici di contatto si deformano, creando un'area di contatto finita. Ciò si traduce in una distribuzione delle forze normali in ogni punto di contatto.
La sezione anteriore di quest'area subisce una deformazione, che ritarda il movimento di rotolamento.
Al contrario, la sezione posteriore subisce un restauro relativamente più piccolo che spinge il pneumatico in avanti.
La forza normale risultante che agisce in A è la somma di queste forze.
Per mantenere il pneumatico in movimento a una velocità costante e bilanciare il momento del peso intorno ad A, è necessario applicare una forza motrice orizzontale al centro del pneumatico. Qui tutte le forze devono essere concorrenti.
La condizione di equilibrio del momento nel punto A fornisce la forza motrice in termini di coefficiente di resistenza al rotolamento.
Il peso moltiplicato per il coefficiente di resistenza al rotolamento sul raggio è solitamente inferiore al coefficiente di attrito cinetico moltiplicato per il peso.
Quindi, la forza di attrito volvente è inferiore alla forza di scorrimento.

<ol>
	<li>Hibbeler, R.C. (2016). Ingegneria Meccanica \u2012 Statica e Dinamica. Hoboken, New Jersey: Pearson Prentice Hall. pp 452 \u2012 439.</li>
	<li>Meriam, J.L.; Kraige, LG e Bolton, JN (2020). Ingegneria Meccanica \u2012 Statica. Hoboken, New Jersey: John Wiley. pagine 372.</li>
	<li>Birra, F.P.; Johnston, E.R.; Mazurek, D.F; Cromwell, P.J. e Self, B.P. (2019). Meccanica vettoriale per ingegneri \u2012 Statica e dinamica. New York: McGraw-Hill. pagine 469.</li>
</ol>

resistenza al rotolamento

Quando un cilindro solido rotola regolarmente su una superficie rigida, la forza normale applicata dalla superficie sul cilindro, è perpendicolare alla tangente nel punto di contatto. Tuttavia, poiché nessun materiale è completamente rigido, la reazione della superficie al cilindro coinvolge una gamma di pressioni normali.

Ad esempio, immagina un cilindro duro che rotola su una superficie relativamente morbida. Il peso del cilindro comprime la superficie sotto di esso. Mentre il cilindro si muove, il materiale davanti rallenta a causa della deformazione mentre il materiale dietro si riprende dal suo stato deformato, spingendo il cilindro in avanti. Le pressioni normali che agiscono sul cilindro in questo modo sono rappresentate dalle loro forze risultanti, Nd e Nr. La forza di deformazione (Nd) e la sua componente orizzontale, sono consistentemente più grandi della forza di ripristino (Nr), richiedendo una forza di guida orizzontale da esercitare sul cilindro per mantenere il suo movimento.

La resistenza al rotolamento si verifica principalmente a causa di questo effetto, anche se è influenzata, in misura minore, dall'adesione superficiale e dallo scivolamento microrelativo tra le superfici di contatto.

Per spiegare ulteriormente questo concetto, considera un pneumatico che rotola a velocità costante. Le forze principali che agiscono su di esso sono il suo peso, che agisce verticalmente verso il basso, e la forza normale esercitata dal terreno, che agisce verticalmente verso l'alto. Mentre lo pneumatico rotola, la sezione anteriore dell'area di contatto subisce deformazioni, che ritardano il moto di rotolamento dello pneumatico. Al contrario, la sezione posteriore subisce un ripristino relativamente minore che spinge lo pneumatico in avanti. L'effetto netto è che la forza normale risultante che agisce sul punto A (il centro dell'area di contatto) è la somma di queste forze contrastanti.

<img alt="Figure 1" src="/files/ftp_upload/14328/14328_Figure_1v2.svg" style="text-align: center; height: 350px;" />

Per mantenere lo pneumatico che rotola a velocità costante e bilanciare il momento del peso rispetto al punto A, è necessaria una forza di guida orizzontale (F) applicata al centro dello pneumatico. Per l'equilibrio, tutte le forze che agiscono sullo pneumatico devono essere coincidenti. Utilizzando la condizione di equilibrio del momento al punto A, possiamo determinare la forza di guida necessaria per mantenere una velocità costante in termini del coefficiente di resistenza al rotolamento (a).

<img alt="Equation 1" src="/files/ftp_upload/14328/14328_Equation_1v2.svg" style="text-align: center; height: 28px;" />

Questa forza di guida è di solito inferiore al prodotto del coefficiente di attrito cinetico per il peso dello pneumatico.

<img alt="Equation 2" src="/files/ftp_upload/14328/14328_Equation_2v2.svg" style="text-align: center; height: 28px;" />

Questa relazione implica che la forza di attrito di rotolamento è tipicamente inferiore alla forza di scivolamento sperimentata quando uno pneumatico slitta su una superficie. Di conseguenza, la resistenza al rotolamento è generalmente meno dannosa per le prestazioni di un veicolo rispetto all'attrito di scivolamento.

Resistenza al rotolamento

Quando un cilindro solido rotola costantemente su una superficie rigida, la forza normale applicata dalla superficie sul cilindro è perpendicolare alla tangente ...

Education

Didattica

JoVE Core

Mechanical Engineering

Ingegneria Meccanica

Unit 1

Unità 1

Friction

Attrito

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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Tire Deformation and Rolling Resistance

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