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 transmitter from a researcher's boat sends a signal to the seabed of waves speed 300m/s and it takes 5 seconds for the signal to return back to the boat. Calculate the depth of the sea there.
A ball is rolled, travelling 10 m north in 5s, then 10 m east in 10s. What is the total distance and average speed of the ball? What is the total displacement and average velocity of the ball?
The friction coefficient of Formula 1 car tyres are around 1.7 in dry weather. Assuming sufficient power from the engine, calculate the theoretical best 0-100 km/h acceleration time in seconds. (neglect downforce, g=9.81m/s^2)
A uniform plank of wood of mass 32 kg and length 4.0 m is used to cross a ditch. In the ditch is a rock, which is used to support the plank horizontally 0.80 m from one end. The other end is supported by the bank. Calculate the rock's supporting force.