...Gravitational Potential Energy... (1 Viewer)

[ausm8]

Hi,
I have a question, and google wasnt rather helpful, so i am posting it here.

Ep = -G m1 m2
r
The above formula has a negative sign. Why is this? The closer you get to Earth, does the value get bigger or smaller?


Can someone please clarify this.

Cheers.

 

[Riviet]

You should search the boredofstudies forums instead, because there have been similar threads made about this. Click here

 

[ausm8]

Yes i was planning to search, but my internet was rather slow due relatives finsihing off the quota.

Thanks for your help, appreciated


Cheers

 

[Ghost1788]

the formula is well explained in most textbooks.

but if u didnt read it or have a book that is one of the minority that doesnt explain it then here goes(though considering that its a syllabus dot point...)

GPE is thought of the work required to move an object from a point to infinity however by doing that on say Earth you are moving the object in a direction opposite to the direction of the gravitational field which is directed towards the earth. in this case gpe is positive. however if you think of moving the object from a point on earth to infinity you are moving the object against the direction of the field and thus the negative sign appears


---if u can have a look at a jacaranda text book ur question is answered well---

/Ghost

 

[KeypadSDM]

More simply, if you have a greater radius, you should have more potential energy [takes work to put you up there].

 

[Halfasian89]

Yeh its like that, but i like to see the whole thing as:

a gravitational field doesn't store energy into an object, it rather provides masses kinetic energy, the OPPOSITE to potential energy, and in that respect you see the logic of the negative sign, for there is negative potential energy existant in respect to gravitational fieds.

Observing the formula, distance is inversely proportional to gravitational energy, so as an object becomes closer to earth, the magnitude of gravitational potential energy increases but it is negative, so therefore there is much lower gravitational potential energy (ie. greater kinetic energy). Logically, if an object was an infinite distance away from earth, GPE would be zero

 

[Stan..]

I always thought it was due to the conservation of energy, that when the object moves futher away from the large object it has to do work against gravity. That it's energy has to decrease as it's approaching infinity rather than increase, that would violate the conservation of energy. Thus, E_g = -G mm1/r^2.

EDIT: Keypad beat me to it.