wrx said:
Hmm I now have some problems on understanding the concept of negative gravitational potential energy. Some questions have the negative sign, some dont?? Am i missing something here? How can an object have a negative gpe, if gpe is the like, the higher the object the more gpe it has, and the lcloser it is to the mass, the less gpe it has.
All the above is correct.
An object is going to have GPE when it is in a gravitational field. So the further you are away from the object the greater the GPE.
The only point without a gravitational field is at a distance of infinity. This point therefore will have absolute zero potential energy. Any point closer than this must have less GPE than zero as you are moving closer to the object so less GPE. The only way this can be is if the GPE is negative.
You can also explain it in terms of work. If you don't understand above. I can try that.
If an object hits earth, wouldn't it have zero gpe when it is lying on the ground? How can you have negative gpe??
What is your reference?
What you wrote here is the traditional reference. However, if you dug a hole under the object it would then have potential energy again because it is going to fall to the bottom of the hole. So now the bottom of the hole is zero. So your original point couldn't have been zero. This can keep going. This is why they define zero as at an infinite distance from Earth, where the gravitational force is zero.
ps. If you have a question ask. I didn't substitute G in the other point to reduce the need for exponentials. A lot of students type exponentials wrong on their calculators and because GM was a constant, it was as easy to find GM as just M by itself.
