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ZeinabSayed
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why there is no work done when one is holding weight?
there isno work done when moving while carrying a school bag?
there isno work done when moving while carrying a school bag?
Jano L. said:That does not mean that you do not lose energy - exerting force by skeletal muscles requires that they spend energy, and you will get tired. I think there are other kinds of muscles, which can exert force without such great exhaustion, perhaps like those of seashells.
On what is this work done then?The work done BY your muscles is not the work done ON the weight you lift.
That is true, there may be microscopic work done on fibres, conserving or not conserving energy. However, don't you think this is irrelevant for the original question? As far as there is no macroscopic work, it is OK to say just there is no work, because that is what textbook rightly say and what the original question was about.You can't support the principle of Energy Conservation yet say there is no difference between what happens in the muscles (which metabolise food) and what happens to the stationary weight.
Jano L. said:That is true, there may be microscopic work done on fibres, conserving or not conserving energy. However, don't you think this is irrelevant for the original question? As far as there is no macroscopic work, it is OK to say just there is no work, because that is what textbook rightly say and what the original question was about.
mg188 said:wouldn't all those atoms in the table moving in reaction to the force of an object "resting" on the table be the distance component of F*D?
Are your muscles constantly twitching in a way that helps them to their job? I'm not sure, but either way you look at it, there is no paradox here: Your muscles are simply a zero efficiency machine.sophiecentaur said:You can't support the principle of Energy Conservation yet say there is no difference between what happens in the muscles (which metabolise food) and what happens to the stationary weight. That is unless you want a paradox in a most basic bit of Physics. The difference between your arm and a table top is that there are constant movements in the muscle fibres, there must be hysteresis involved in this movement. These give a force times distance inside the muscles - which resolves any paradox.
russ_watters said:Are your muscles constantly twitching in a way that helps them to their job? I'm not sure, but either way you look at it, there is no paradox here: Your muscles are simply a zero efficiency machine.
I'm sure you can think of other devices that have an input of energy but no output of work.
But they are just fighting each other and not actually making the book move, right? Or another way; even if the book is vibrating ever so slightly, it doesn't, over time, change its elevation. Zero work being done on the book. You asserted an apparent paradox in that. I see none.sophiecentaur said:Afaiaa, muscle fibres cannot just stay contracted. Other fibres need to take over in order to maintain a lift force. This involves a constant process of force times distance with successive parts of the muscles.
russ_watters said:But they are just fighting each other and not actually making the book move, right? Or another way; even if the book is vibrating ever so slightly, it doesn't, over time, change its elevation. Zero work being done on the book. You asserted an apparent paradox in that. I see none.
ZeinabSayed said:why there is no work done when one is holding weight?
there is no work done when moving while carrying a school bag?
Work is defined as the product of force and displacement in the direction of the force. When holding a weight, there is no displacement in the direction of the force, therefore no work is done. The weight is not being moved from one point to another, so there is no change in its position or energy.
Yes, energy is expended when holding a weight, but it is not considered work. The body uses energy to maintain the position and support the weight, but there is no movement or displacement in the direction of the force, so no work is done.
Holding a weight requires the muscles to contract and expend energy, which can lead to fatigue. This is because the muscles are working against the force of gravity to keep the weight in a fixed position, which can be strenuous over time.
Work is a measure of energy transfer or change in energy, while effort is the physical or mental exertion required to accomplish a task. When holding a weight, effort is being exerted, but no work is being done because there is no change in energy or displacement.
Yes, work can be done when holding a weight in a different position, such as lifting or moving it from one point to another. In this case, there is a displacement in the direction of the force, and therefore work is being done. The weight is being moved and its position and energy are changing.