Why a Wheel Moves When Rotated - Understanding Torque & Force

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Discussion Overview

The discussion revolves around the mechanics of why a wheel translates when it rotates, focusing on the concepts of torque, force, and friction. Participants explore the relationship between applied forces, counterforces, and the role of static friction in preventing slipping.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why the counterforce from the ground does not prevent the wheel from translating when it rotates, seeking clarification on the interaction of forces.
  • Another participant explains that the force is "unbalanced," suggesting that an equal and opposite force at the top of the wheel would stop the wheel without translation, highlighting the role of a single force in producing both rotation and translation.
  • A participant notes the necessity of static friction for a wheel to rotate without slipping, implying that slipping would occur without it.
  • Another participant discusses the implications of sliding friction, specifically in the context of vehicle braking performance during skidding.
  • One participant raises the complexity of forces acting on a car's wheels, mentioning engine power, friction, and internal forces, and uses an analogy involving a skateboard to illustrate unbalanced forces leading to motion.
  • A later reply references Newton's third law in relation to the forces discussed, although it does not clarify the implications for the original question.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the mechanics of wheel motion, with no consensus reached on the specific dynamics involved. The discussion includes multiple competing explanations and interpretations of the forces at play.

Contextual Notes

The discussion does not resolve the assumptions regarding the nature of forces, the definitions of friction types, or the specific conditions under which the wheel operates.

Who May Find This Useful

This discussion may be of interest to individuals studying mechanics, physics students exploring rotational dynamics, or anyone curious about the principles of motion and force interactions in mechanical systems.

peter86
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Why does a wheel move (translate) when it rotates? I mean when you exert a force somewhere on the wheel, it will produce a torque that make it rotate. Now assuming the wheel is in contact with the ground, the wheel will then exert a force on the ground and the ground will exert a counterforce on the wheel. So why doesn't this counterforce counteract on the torque of the wheel and prevent the rotation instead of translation the wheel?

I've been wondering about this for quite some time now but I've found no explanation of it.
 
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Because the force is "unbalanced". If you had an equal (and opposite) force at the top of the wheel, then you would stop the wheel without it translating. A single force acting on an object somewhere other than the center of mass gives both a turning moment and a translation. You have to have a "couple" to get only a turning moment.
 
Do you know this? If a wheel rotates, then it is essential that static friction has to act on it. Otherwise it will start to slip or slide.
 
Which is called sliding friction and also explains why cars don't brake very well when they are skidding.
 
Consider a car: what is the source of the forces on the wheels? You have the engine, you have friction with the ground, you have internal friction inside the engine and drivetrain. The friction inside the drivetrain might cut 20% from your engine power, a lot going to the ground. The force of friction may include the ground pushing against the wheel and the wheel pushing against the wall, but that doesn't make the forces on the car balanced. Consider standing on a skateboard and pushing against a wall - the wall pushes back with the same force you push on the wall, and you move.
 
Which is called Newtons third law
 

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