The Physics of Carrying a Load: Why Does the Height Remain the Same?

In summary, the conversation discusses the concept of work and energy expenditure in relation to stationary objects and humans. It is explained that even though energy is constantly being expended by humans, in terms of purely mechanical work, no work is being done. This is because the human effort does not oppose the weight of the load. The example of a fridge magnet stuck on a fridge is used to illustrate this concept.
  • #1
lewis198
96
0
Here is an interesting question I thought about:

If a man carries a load x/(g*d) above his head, and his arms do work x, and his legs now have the added work x, over d meters, why does the load remain at the same height?
 
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  • #2
Simply put, the arms and legs do no actual work in the vertical direction and since [tex]W = \int_{x1}^{x2} F \cdot dx[/tex] , the work done by or to the load is 0 and thus won't move in height.
 
  • #3
But if the load is to remain stationary wouldn't they have to oppose the weight? Isn't energy expended when the man is stationary? You see this is what I don't get in physics, some basic things don't match up. For example, a 0.5 kg fridge magnet stuck on a fridge for years is supposed to do no work but if we were to cling to a rock face for years and years we would expend energy. How is that explained?
 
  • #4
lewis198 said:
But if the load is to remain stationary wouldn't they have to oppose the weight? Isn't energy expended when the man is stationary?

You expend energy all the time no matter what you do, just to keep your body running, etc. But in terms of purely mechanical work, no work is being done. You're confusing human effort with work. A table has no problem holding something up either. Do you think tables are performing work?

You see this is what I don't get in physics, some basic things don't match up. For example, a 0.5 kg fridge magnet stuck on a fridge for years is supposed to do no work but if we were to cling to a rock face for years and years we would expend energy. How is that explained?

Same answer: Stop anthropomorphizing.
 
  • #5
lewis198 said:
But if the load is to remain stationary wouldn't they have to oppose the weight? Isn't energy expended when the man is stationary? You see this is what I don't get in physics, some basic things don't match up. For example, a 0.5 kg fridge magnet stuck on a fridge for years is supposed to do no work but if we were to cling to a rock face for years and years we would expend energy. How is that explained?
This question comes up a lot. Here's one thread that might help you sort it out: https://www.physicsforums.com/showthread.php?t=119026
 

1. What does "impossible by definition" mean?

"Impossible by definition" means that something is impossible because it goes against the very definition of the term or concept. It is inherently contradictory or illogical.

2. Can something be both impossible by definition and still possible?

No, if something is impossible by definition, it means that it cannot exist or happen in any circumstance. It is a concept or idea that is logically impossible to achieve.

3. How is something determined to be impossible by definition?

Something is determined to be impossible by definition through careful analysis and examination of its definition and characteristics. If it is found to contain contradictions or violate logical principles, it is deemed impossible by definition.

4. Are there any real-world examples of something that is impossible by definition?

One example of something that is impossible by definition is a square circle. By definition, a circle is a shape with no sides or corners, while a square has four sides and four corners. It is impossible for these two concepts to coexist in one object, making a square circle impossible by definition.

5. Can the concept of "impossible by definition" change over time?

Yes, the concept of "impossible by definition" can change over time as our understanding and definitions of certain terms or concepts evolve. What was once deemed impossible by definition may become possible as our knowledge and technology advances.

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