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.

 

[asteriatic]

for your question. In regards to the change in gravitational potential energy (Grav PE) with a change in origin, it is important to note that Grav PE is a relative quantity that depends on the position of the object in a gravitational field. In this scenario, we are assuming a constant gravitational field near the Earth's surface.

When the object is at a height of 1.5 m, it has a Grav PE of 14.7 J relative to the ground. As it falls to the ground, its Grav PE decreases to 0 J as it approaches the ground, as you correctly stated.

However, if we move the origin to the position of the object, which is now at 0 m, the object's Grav PE would be 0 J at the new origin. As the object falls towards the ground, its Grav PE would decrease to -14.7 J as it approaches the ground. This is because the new origin is now at the same level as the object, so the distance between the object and the ground is now 1.5 m, and the object's Grav PE is negative as it is closer to the ground.

In summary, the object's Grav PE is always relative to the origin chosen, and it will change depending on the position of the object in the gravitational field. Moving the origin to the position of the object will not change the overall change in Grav PE, but it will change the values relative to the new origin. I hope this helps clarify the concept of Grav PE in relation to changes in origin.