Is this because the other equation for work is W=FsW=Fs, where W is the work, F is the force, and s for the displacement? Even though that there force acting on the wall but there is no displacement, so work done is zero?

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Is this because the other equation for work is W=FsW=Fs, where W is the work, F is the force, and s for the displacement? Even though that there force acting on the wall but there is no displacement, so work done is zero?

Real World Connections: When Work Happens
Note that work as we define it is not the same as effort. You can push against a concrete wall all you want, but you won't
move it. While the pushing represents effort on your part, the fact that you have not changed the wall's state in any way
indicates that you haven't done work. If you did somehow push the wall over, this would indicate a change in the wall's state,
and therefore you would have done work.
This can also be shown with Figure 7.2(a): as you push a lawnmower against friction, both you and friction are changing the
lawnmower's state. However, only the component of the force parallel to the movement is changing the lawnmower's state.
The component perpendicular to the motion is trying to push the lawnmower straight into Earth; the lawnmower does not
move into Earth, and therefore the lawnmower's state is not changing in the direction of Earth.
Similarly, in Figure 7.2(c), both your hand and gravity are exerting force on the briefcase. However, they are both acting
perpendicular to the direction of motion, hence they are not changing the condition of the briefcase and do no work.
However, if the briefcase were dropped, then its displacement would be parallel to the force of gravity, which would do work
on it, changing its state (it would fall to the ground).
Transcribed Image Text:Real World Connections: When Work Happens Note that work as we define it is not the same as effort. You can push against a concrete wall all you want, but you won't move it. While the pushing represents effort on your part, the fact that you have not changed the wall's state in any way indicates that you haven't done work. If you did somehow push the wall over, this would indicate a change in the wall's state, and therefore you would have done work. This can also be shown with Figure 7.2(a): as you push a lawnmower against friction, both you and friction are changing the lawnmower's state. However, only the component of the force parallel to the movement is changing the lawnmower's state. The component perpendicular to the motion is trying to push the lawnmower straight into Earth; the lawnmower does not move into Earth, and therefore the lawnmower's state is not changing in the direction of Earth. Similarly, in Figure 7.2(c), both your hand and gravity are exerting force on the briefcase. However, they are both acting perpendicular to the direction of motion, hence they are not changing the condition of the briefcase and do no work. However, if the briefcase were dropped, then its displacement would be parallel to the force of gravity, which would do work on it, changing its state (it would fall to the ground).
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