Question

do only attractive forces bring about negative ENERGY?

Answer 1

By convention, for forces such as gravity and electricity, we set the point at infinity to be the zero energy level. The results in energy level of charges and objects being negative. But that is a completely arbitrary choice. We could make anywhere else the zero energy level. But it makes computation easier to do it this way.

In other words, don't over interpret the fact that there are negative energy levels. What really matters is changes in energy, i.e., work. For the purposes of change in energy level, any value of zero will do, provided it is consistent.

Answer 2

From chat (for others who are interested in this question)

salini: in the physical meaning,p.e of a body is negative as it is bound (attracted)to some body like that but if i change my chosen infinity point where total energy is 0 then p.e becomes positive? 10:35 am Report Delete

JamesJ: If for example I define gravitational PE of the earth to be zero at sea level, then right now I have positive gravitation PE, because I'm above sea level.

JamesJ: *gravitational

salini: that is the point where total energy is made zero?

salini: sea level

JamesJ: For forces like gravity, it's arbitrary. Hence in that definition, if I were at sea level and had zero velocity, my total mechanical energy would be zero.

JamesJ: because my PE = 0 and my KE = 0

salini: thank you very much for ur answers