Conservative Forces: The Relationship Between Work and Energy Conservation

[mcnealymt]

My question is can work be the transformation of potential energy to kinetic energy ( assuming no energy is lost)? I understand that work is energy transferred to and from the system with a change in the energy of the system. However, if there is no change of energy in the system, how can work still be done?

 

[Legerity]

You have to use the post layout or else you are going against the guidelines of this section of the forum, but at rest PE = 0 and KE = something, but once motion starts to increase PE increases and KE decreases. This peaks when KE = 0 then object in motion starts to slow down and then reverses with PE decreasing and KE increasing, going back to its original of PE = 0 and KE = something.

 

[mcnealymt]

Okay, but in free fall why is gravity doing work on the object if energy is conserved? The book says that in order for the object to get to a certain height it had to be lifted up; and therefore work is stored in the form of potential energy initially. When the object is released from this initial height the energy released is work that gravity does on the ball. For me this is confusing because there no change in energy of the system and no energy is being added or released from the system. Sorry that I posted in the wrong forum.

 

[Legerity]

You did not post in the wrong forum, its just that you simply didn't use the HW post layout shown to you when creating a new thread.

Initially at rest, the object should have PE = 0 and have a KE, but once something breaks the gravitational force of the Earth, then it gains a PE. Also, if gravity was not doing work on the falling object, then what force would be able to bring it back down to the Earth?

 

[mcnealymt]

So energy transformation is also a type of work?

 

[Legerity]

I do not think energy transformation is work, but if a force acts upon an object work is involved. I am kind of confused on what exactly you are confused on. Mind being a bit more clearer?

 

[mcnealymt]

In a situation where an object is released from an initial height(off the ground) and is falling towards the ground. My question is if energy is being conserved then why is work being done. The only way in which energy can be conserved is if there no change in the systems energy or there is an energy transformation, then why is gravity doing work on the object if there's no change in energy.

 

[Legerity]

In a situation where an object is released from an initial height(off the ground) and is falling towards the ground. My question is if energy is being conserved then why is work being done. The only way in which energy can be conserved is if there no change in the systems energy or there is an energy transformation, then why is gravity doing work on the object if there's no change in energy.

The energy will change during the motion, but once it comes to stop, it will be the same as where it started. Work done by gravity on the object (-ΔPE) is needed to move the object. Without a force, there is no work, and without those two the object will be unable to move.

 

[mcnealymt]

Okay that makes sense. Sorry I wasn't being clear. So basically as long as a force is applied to an object and there is a change in displacement, then work is being done; regardless of energy transformation or transfer.

 

[Legerity]

Yes, that is correct.

 

[mcnealymt]

Thank you, I highly appreciate it.