# B Calculating the P.E. of a system

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1. Nov 6, 2018 at 7:55 PM

### Hawkingo

Let, we want to calculate the P.E(potential energy) of a system containing 3particles p1,p2,p3.the point of observation is P.so now we should add up the P.E at P due to p1,p2,p3 to get the net potential energy of the system,but why we take the P.E of particles due to each other into count instead of the previous method.I can't figure it out.

2. Nov 6, 2018 at 8:59 PM

### Staff: Mentor

It would help us all if you could post much more information about the situation you are working with...
• PE = GPE or does it include other types of PE?
• If GPE, are you able to assume that the total energy = the sum of the particles' GPE + KE?
• If GPE, is all of the mass in the three particles?
• If so, what are the relative masses of your point particles?
• And what software are you wanting to simulate this problem with?

3. Nov 6, 2018 at 9:15 PM

### Hawkingo

Yes ,I am talking about the GPE and here K.E is 0 and the mass of the system is in the 3 particles.but the system and point of observation both are stationary so I think their masses are absolute and I am not using any simulation software I am just doing with pen and paper.

4. Nov 6, 2018 at 11:03 PM

### Mister T

Potential energy is not the same thing as potential.

You can calculate the potential at point P, and it doesn't involve interactions between $p_1$, $p_2$, and $p_3$.

On the other hand, you can calculate the potential energy of $p_1$, $p_2$, and $p_3$. This does involve the interactions between $p_1$, $p_2$, and $p_3$. The point P is not relevant here. It makes no sense to speak of the potential energy at P. The potential energy is not something that you assign to a point. It's something you apply to the collection $p_1$, $p_2$, and $p_3$.

5. Nov 7, 2018 at 12:02 AM

### Hawkingo

Don't get me wrong,I want to ask that for example we want to calculate the center of mass of a system and that value is applied to that system because when we measure the mass of the system it appears to be concentrated at the center of mass but in case of G.P.E of a system when we have to measure it we have to observe it by a point of observation and that value varies from point to point.I know I have some misconception but I can't figure it out so I need help.

6. Nov 7, 2018 at 6:37 AM

### Mister T

The potential energy of a collection of particles does not vary from point to point.

7. Nov 7, 2018 at 6:41 AM

### Hawkingo

Got it, thanks