The light saber might not weigh much, but I advice you to pick something light up and start swinging it around, then you start jumping around and finally you start jumping and rolling while swinging this 'light object of unknown description'. Then when you're out of breath and flailing on the floor gripping your chest, you ask your question again, and you will have your answer. And using the force is exhausting, it's not a endless font of power if I understand things correctly.
MvH
Suiken.