## Internal Energy

Vanessa Romero-Campos 2B
Posts: 39
Joined: Fri Sep 25, 2015 3:00 am

### Internal Energy

In class, we went over an example that talked about a piston moving out and the energy of the system decreasing by an amount. The first diagram showed the formula F=P*A and the second showed that V=A*d. Why is it that the volume is the area times displacement of the piston? Why does it only take into consideration the volume of the part that was displaced rather than the entire systems volume?

I have attached a picture of the diagram i was talking about down below.
Attachments
illustrations

Sandhya Rajkumar 1C
Posts: 50
Joined: Fri Jun 23, 2017 11:40 am

### Re: Internal Energy

In the diagram, I believe that the volume is area x displacement of the piston because we need to calculate the change in volume (delta V) not the volume of the entire system. And so in order to calculate the change in volume, we would multiply the area and the distance that the piston has been displaced.

Sarah Maraach 2K
Posts: 31
Joined: Thu Jul 27, 2017 3:00 am

### Re: Internal Energy

If you look at it mathematically, delta V is final V minus initial V, therefore your change would equate to the amount displaced. But, overall, we really are using the values of the entire system’s volume, just using the actual change between the two volumes.

Erik Khong 2E
Posts: 50
Joined: Fri Sep 29, 2017 7:07 am

### Re: Internal Energy

The formula requires the delta V because we are trying to calculate how much the system changed overall.