Why is there no work for someone walking on flat plane

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    Flat Plane Work
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Discussion Overview

The discussion centers around the concept of work in physics, particularly why there is no work done in the horizontal direction when a person walks on a flat plane, while work is done in the vertical direction when climbing an inclined plane. Participants explore definitions of work, the role of force and displacement, and the implications of these concepts in different scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants explain that work is defined as the product of force and displacement, with the angle between them affecting the calculation (Post 2).
  • There is a discussion about why the cosine function is used in the work formula, with some participants questioning why it is not sine (Post 3, Post 7).
  • One participant argues that the human body is inefficient and that walking on a flat surface involves energy expenditure despite no work being done in the horizontal direction (Post 4, Post 5).
  • Another participant describes the mechanics of a single horizontal step, suggesting that while mechanical work is done, it does not result in a change in potential or kinetic energy (Post 6).
  • Some participants assert that the net force in the horizontal direction is zero, leading to no work being done, while others challenge this assumption and seek clarification (Post 10, Post 11).
  • There is a contention regarding the relevance of a person's motion before or after walking on an inclined plane to the discussion of work done (Post 12, Post 14).

Areas of Agreement / Disagreement

Participants express differing views on the concept of work in horizontal motion, with some asserting that no work is done while others challenge this notion. The discussion remains unresolved, with multiple competing perspectives on the definitions and implications of work in various contexts.

Contextual Notes

Participants highlight the conflict between formal definitions of work and practical experiences, noting that the human body's inefficiency complicates the understanding of energy expenditure during walking (Post 9).

  • #31
zanick said:
rolling can still have friction.. "rolling without friction" allows you to calculate the work used strictly to move the object from one point to another.
If it's rolling, the presence or absence or degree of friction with the surface makes no difference. You may be thinking of rolling resistance.
 
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  • #32
haruspex said:
If it's rolling, the presence or absence or degree of friction with the surface makes no difference. You may be thinking of rolling resistance.
Yes, I am speaking of rolling resistance... is there any other kind that wouldn't make a difference? :)
also, I guess you could consider the extra rotational inertia of the rotating elelments as well ( WR^2)
 
  • #33
zanick said:
Yes, I am speaking of rolling resistance... is there any other kind that wouldn't make a difference? :)
If there's rolling resistance, that will apply equally with or without friction. The difference is that with friction both rotational and translational speeds will fall (in step); without friction only the rotational speed is affected - but as soon as that happens it is no longer considered rolling.
 
  • #34
haruspex said:
If there's rolling resistance, that will apply equally with or without friction. The difference is that with friction both rotational and translational speeds will fall (in step); without friction only the rotational speed is affected - but as soon as that happens it is no longer considered rolling.
never hear about this type of stuff, would it only be affected without friction if the ball was not a perfect sphear? if not how would it lose any rotational speed?
 
  • #35
Jewish_Vulcan said:
never hear about this type of stuff, would it only be affected without friction if the ball was not a perfect sphear? if not how would it lose any rotational speed?
It's not the shape, more the rigidity.
Real world objects are not completely rigid. A tyre deforms as it rotates, producing a flat area in contact with the road. This constant deformation takes work. But rolling resistance is not limited to that. It might be mostly that, but the term is a catch-all encompassing other losses as such axle friction.
 
  • #36
haruspex said:
It's not the shape, more the rigidity.
Real world objects are not completely rigid. A tyre deforms as it rotates, producing a flat area in contact with the road. This constant deformation takes work. But rolling resistance is not limited to that. It might be mostly that, but the term is a catch-all encompassing other losses as such axle friction.
I was referring to, rolling friction being illuminated, but still the force to accelerate the mass translationally and rotationally and then to decelerate it, would be needed to calculate the work done over time. (power).
 
  • #37
zanick said:
I was referring to, rolling friction being illuminated,
I guess you mean eliminated.
zanick said:
but still the force to accelerate the mass translationally and rotationally and then to decelerate it, would be needed to calculate the work done over time. (power).
You've lost me.
 

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