GPE question. (1 Viewer)

[lolJK]

hey, just wanted an insight into how you would answer this question

"Outline the rationale behind choosing infinity as the point where objects in space have zero Ep"

I was going along the lines of saying that that is the point where the gravitational field stops. Is this right? Would you add anything?

Thanks, lolJK

 

[taeyang]

Well the gravitational field doesn't stop, it just gets to an impossibly small value via the formula



Anyway, it makes sense because due to the formula



We can see that as the radius approaches infinity, as a result of the inverse square relation, the Gravitational Force will approach an infinitely small number.. so it makes sense in this regard.

BUT it doesn't matter where you place "zero" in respect to GPE.

 

[ohexploitable]

because it is the only point where there is truly zero energy

 

[Jaymay]

The formula PE=mgh gives us the potential energy from earths surface and a point above. here the earths surface is zero.

On a planetary scale, this theory cannot work. the 'zero' point is now a very far distance away from the earths surface, at infinity. Any point between a planets surface must be a negative number (when staying in the same orientation to Normal potential energy)

 

[Fizzy_Cyst]

In order for an object to have GPE it must be present in a gravitational field, so that it can do work on the field.

At infinity, there is no gravitational field, hence it cannot have GPE as it cannot do work on the field.

Therefore GPE at infinity would be zero

 

[clementc]

I always hated GPE T___T
I think the reason was that because GPE is always relative to your reference zero point i.e. depending on where I set GPE to be zero, everything else will change. So they wanted to choose a point that was the same for everything, which was like at infinity where the GPE was zero. So you can do stuff like easily calculate the energy needed to escape from any planet, as opposed if you set it in a really weird position like the moon.

 

[httton]

heres a nice analogy to get your head around the whole negative sign.

at a big distance there is 0 GPE correct?

so when your object begins to accelerate towards the body, it must lose GPE to gain KE right?

0 minus any +ve value is -ve gotcha?