So gravity is a force, and when it pulls on an object the object gains kinetic energy. However, doesn’t this mean that energy is being “created”, since the object gains kinetic energy? Why doesn’t this violate the first law? It seems that energy is just created and then destroyed (when the object stops moving). Please don’t be too complex in explaining, as I do have some knowledge but am not an expert. Also, isn’t potential energy not really energy, just a way of keeping track of the energy an object has? Doesn’t that make it not a justifiable response for this?
When two gravitating bodies are far apart, their gravitational potential energy is at a maximum- since it required the expenditure of work to pull them apart. As they draw nearer to one another, their gravitational potential energy decreases and their kinetic energy increases. The first law is therefore not violated: the total energy of the system is conserved.
No energy can never be created nor destroyed but can change from one energy form to another.
The gain in kinetic energy you mean is actually due to the loss in gravitational potentional energy denoted by Ø = -GM/r or simply G.P.E = mgh.
- 1. Just like potential energy, the biggest value of potential you can get is zero. All other values are less than zero - i.e. negative!! 2. Potential is not a vector even though it has a negative sign. It doesn't have a direction, only a magnitude. -
Just imagine in space there are no other forces acting on an object and you apply a force in a particular direcion . Then the object will travel forever unless there is an opposing force which either stop it or change its direction.
So when object stops moving which it needs an opposing force to start decellarating . When this happens the Kinetic energy will be converted to kinetic energy ,light energy or etc... If you take at intial anf final energy levels its all the same and the energy was never destroyed or created.