Change in Grav PE with the change in origin.

[mrhingle]

If a 1kg object is 1.5 m heigh. I find its PE to be 14.7 J. If it falls to the ground, the PE of 14.7 J goes to 0 as the object approaches the ground. Right?

Now say the origin has been moved to 1.5 m where the object lies. Is the object at 0 J at the origin and approaching -14.7 J as it approaches the ground?

Thanks

 

[gneill]

If a 1kg object is 1.5 m heigh. I find its PE to be 14.7 J. If it falls to the ground, the PE of 14.7 J goes to 0 as the object approaches the ground. Right?

Now say the origin has been moved to 1.5 m where the object lies. Is the object at 0 J at the origin and approaching -14.7 J as it approaches the ground?

Thanks

Hi mrhingle, welcome to PF.

Yes, changes in PE are relative to a chosen zero reference. If you place the zero reference for PE at an origin at a given height, then excursions below that height are associated with negative values for the PE.

 

[mrhingle]

Would both cases be a negative change in PE?

 

[gneill]

Would both cases be a negative change in PE?

ΔPE = PE_final - PE_initial

If ΔPE is positive then the change is positive. If ΔPE is negative then the change is negative.