Work Done & Friction: Definition & Effect

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Discussion Overview

The discussion revolves around the concept of work done by friction on a moving car, exploring definitions of work and the effects of friction in different scenarios, including acceleration and braking. Participants examine the implications of friction's direction relative to the motion of the car and the tires.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether friction does work on a moving car, suggesting that if friction acts in the opposite direction to the car's motion, it may not fit the standard definition of work done.
  • Another participant clarifies that if the car moves to the right while friction acts to the left, the work done by friction would be negative, particularly in the context of braking.
  • A third participant expresses gratitude for the clarification provided, indicating that the explanation helped them understand the concept better.
  • Another participant describes the motion of a tire in relation to friction, noting that while the car moves forward, the point of contact on the tire moves left relative to the road, suggesting that friction acts in the direction of the car's motion.
  • One participant states that the direction of friction varies depending on whether the car is accelerating or decelerating, emphasizing that friction opposes slipping between surfaces.

Areas of Agreement / Disagreement

Participants express differing views on the nature of work done by friction, with some asserting that friction does negative work when opposing motion, while others highlight the complexity of friction's role depending on the car's acceleration or deceleration. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants have not fully defined the conditions under which friction acts or clarified the assumptions regarding the direction of forces and motion, leaving some aspects of the discussion open to interpretation.

Griff38
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If work done is defined as F X distance moved in the direction of this force, is friction doing work on a moving car since if the car is moving to the right friction is actually acting to the left? or should the definition of work done be F x distance moved parallel to the line of action of this force in which case the displacement and force can be in totally opposite directions.
 
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If the car moves to the right but friction acts to the left, then the work done will be negative. That would be the case when braking. If the car is accelerating, then the force will point in the direction of motion and the work done will be positive.
 
Thank you so much, that's made it very clear.
 
Consider a car moving forward to the right as you look at the car. This implies the the tires rotating in a clockwise direction. As a point on the tire comes around to the bottom where it contacts the road, the direction the tire is moving relative to the road is to the left. Friction, in this case, is then applied to the tire toward the right --> in the direction of the cars motion. As previously mentioned, friction acts opposite to the direction of motion. The "motion" being the motion of the tire.
 
The direction of friction depends on whether the car is accelerating or deaccelerating. Friction acts to oppose slipping between the surfaces.
 

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