Why is potential energy negative? What does that even mean?
This is really just a definition! When we ask what the potential energy of an object is, we are really asking what energy is available to be extracted. In the case of gravity: two objects separated by an infinite distance are DEFINED to have zero gravitational potential energy. As they fall together their potential energy becomes more negative, and because of the conservation of energy their kinetic energy increases so that the total energy remains zero.
The minus sign in the gravitational potential energy is really just a convention we use to keep track of energy - there is no physical meaning behind it. We could equally define it the other way round so that kinetic energy was negative!
BT
Related Physics A Level answers
All answers ▸A boy (25kg) and a girl (20kg) are playing on a see-saw which is 4m long. If the boy sits 1m from the centre on the left side and the girl 2m from the centre on the other, which direction will the see-saw will rotate around its centre?
A crane is attached to one end of a steel girder, and lifts that end into the air. When the cable attached to the end of the girder is at 20 degrees to the vertical, the tension is 6.5kN. Calculate the horizontal and vertical components of this force.
What is the difference between distance and displacement?
A diver of mass 60kg stands on the end of a diving board (2m in length). Calculate the upward force exerted on the retaining spring which is 30cm from the start of the diving board.