I suspect your girlfriend is not jealous of inanimate objects as much as she feels she is further down your priority list than your motorcyle or computer.
The underlying definition of jealousy is (fear that you love someone more than they love you).
People watch the choices their mates make and compare them to the ones they would make in the same situation. If they aren't the same they question whether or not their mate loves them as much as they love their mate.
For example a guy who is happy with spending every weekend with his girlfriend may become "jealous" when she insists on having weekend getaways with her girlfriends a couple of times a year. In his mind he knows he would not choose to leave her for the weekend to spend time with his buddies. Therefore this raises (questions) that may cause him to feel he loves her more than she loves him.
Oftentimes this leads to arguments/fights between couples. The person who wants to do his/her own thing calls the other person jealous, paranoid, insecure, or needy.
In reality there is no "right" or "wrong" there is only (agree) or (disagree). When two people want the same things and share the same values/beliefs about how a relationship works best there is rarely any jealousy because they have the same (priority list) when it comes to their wants for the relationship.
Ultimately each of us is looking for someone who (naturally agrees) with us on the important things in life. If your mate gets upset over things you have no intention of giving up then it's possible she is just wrong (for you). On the other hand if she is the love of your life you might decide to do whatever it takes to reassure her that she is number one on your list of priorities.