You should be able to turn it without sticking in a finger nail, but it's never going to be really loose like a mouse scroll-wheel. If yours is really stiff something may be physically wrong.
If you use it a lot it will probably loosen somewhat.
If you feel that there is some physical problem then you can get the camera checked at a Panasonic Store if you want to. If there would be any fault they will correct it.
Please revert back and update me with the status of the problem. Thanks. Cheers Nathan