What is the concept of work?

  • #1

Summary:

does work stills is done by the force source only or by the object which is affected by it too ?

Main Question or Discussion Point

if I shoot the football, the ball will recive a force in specific direction, and it would follow that direction.
Does the work is done by me when I shooted the ball, or the ball does work when it moves all the period after my shooting ?
the work includes force and displacement , so who does the work ? the ball or me ?
when the ball moves, the force of shooting becomes 0 ? and it stills keep moving because the inertia ? and not because of the work ?
 
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Answers and Replies

  • #2
A.T.
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so who does the work ? the ball or me ?
Usually, if A does positive work on B, then B does negative work on A. But the magnitudes can differ if there is energy dissipation.
 
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  • #3
Usually, if A does positive work on B, then B does negative work on A. But the magnitudes can differ if there is energy dissipation.
can you answer all my questions please !
 
  • #4
A.T.
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can you answer all my questions please !
These are too many, because you use question marks as commas.

But if there is no force interaction between A & B anymore, then there is no work done between them.
 
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  • #5
russ_watters
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when the ball moves, the force of shooting becomes 0 ? and it stills keep moving because the inertia ? and not because of the work ?
Yes: work is only being done while the force is being applied.
 
  • #6
vanhees71
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This is a bit misleading. If there's a pair interaction in the total energy the interaction potential enters only once!
 
  • #7
gleem
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Work is also a transfer of energy. The transfer occurs during the contact (interaction). In the case of the football the kinetic energy of the foot gives some of its energy to the ball (does work on the ball). This energy results, during the contact, in the compression of the surface of the ball . This compression is the results of the work in stretching the surfaces and compressing the gas inside the ball heating the gas as well as heating the surface and temporarily storing energy in the stretched surface. The elastic surface returns some of the energy as the ball begins to move during the period the foot is in contact with the ball.

In the video note the initial contact and hesitation of the ball to move as it is compressed and its subsequent increase in velocity as the surface rebound converting the stored energy into the motion of the ball.

 
  • #8
Work is also a transfer of energy. The transfer occurs during the contact (interaction). In the case of the football the kinetic energy of the foot gives some of its energy to the ball (does work on the ball). This energy results, during the contact, in the compression of the surface of the ball . This compression is the results of the work in stretching the surfaces and compressing the gas inside the ball heating the gas as well as heating the surface and temporarily storing energy in the stretched surface. The elastic surface returns some of the energy as the ball begins to move during the period the foot is in contact with the ball.

In the video note the initial contact and hesitation of the ball to move as it is compressed and its subsequent increase in velocity as the surface rebound converting the stored energy into the motion of the ball.

Thank you!
I ve understand what you wanted to explain beside the last chapter
you ve said (as the surface rebound converting the stored energy into the motion of the ball).
Did you mean that the surface stretched in the ball make a work on the total ball ?
moving of the ball when no foot is applying happens because the force of the gaz on the surface
 
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  • #9
gleem
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Did you mean that the stored energy in the ball surface make a work on the total ball ?
Basically, If you kick an uncoiled spring it will compress and store energy imparted by the kick. As the foot follow through the spring expands pushing against the foot. The other end of the spring is unhindered so the expansion produces a force in the direction of the motion of the rest of the spring. The spring (ball) bounces off the foot.
 

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