Psychokinesis is the term given to moving objects with mind energy which contains electro magnetic energy, it's also known as PK. In its strongest form it is often associated with poltergeist activity although Poltergeist is a German word meaning "noisy ghost", its definition shouldn't really be attributed to PK because the word doesn't mean that. It was commonly associated with adolescent teenage girls. It can range from raps and taps to moving furniture.
There is no real difference between Psychokinesis and Telekinesis a lot of people think they are different, they are two different words to describe the same thing just like OBES and Astral Projection, OBES being spontaneous and Astral projection is consciously doing it. Psychokinesis is mind over matter, psycho=mind and kinesis=movement, as with an OBE Psychokinesis can sometimes be spontaneous. Telekinesis is movement of objects by thought, like Astral Projection this is a conscious effort to move something, but in both cases they both use the same energy so there is no difference really.
Energy is always there, and always will be, but like with any energy it can be stimulated for example passing an electric current over a magnet will cause movement like in a motor, thus one energy force (electricity) cause another energy force (movement) stimulating the energy, in fact you can apply this theory to things to do with spirit, magnetism, electricity and movement, any 2 of these together will cause the third, movement and magnetism will cause electricity, like with a dynamo, this is one known way how spirit move objects, sometimes when their energy comes into contact with electricity it will cause movement, this is probably why spirit like electrical items so much as they can use the energy to their advantage.
We also have to take into consideration houses that have over head power cables because this can cases disturbances within the house because of the earths magnetic field, again we have electricity and magnetism which causes movement which may be the cause of some poltergeist activity, but saying that spirit can use the energy of the power cables too, so in a house that does have over head power cables it may hard to distinguish from natural energy and spirit energy that cause the activity, when I mean over head cables I'm talking about the really large ones with lots of cables.
Another example of the theory is static electricity, our own energy contains electro magnetic energy and the old party trick of rubbing a balloon on your hair, movement from the balloon being rubbed and the magnetism from our energy which causes electricity.
I came across someone a while back who kept having chairs being moved in the house, I did a reading for this person and found out that there was a lady there who hadn't accepted that she had passed over and was moving the furniture to how she wanted it, as far as she was concerned she hadn't passed over and was carrying on as normal, she saw the person living in the house as an intruder. This is quiet interesting because it shows that spirit can actually interact physically in our world, you've probably had similar experiences objects being moved, missing keys etc, not all spirit people who move things are lost souls most of them are trying to prove their existence to you.