What is convection within the mantle? how does it affect the motion of plates?

The warmer magma is less dense than the cooler magma, so the warmer magma rises and the cooler magma sinks allowing it to be heated. over a long period of time, the movement of the magma causes the plates to move.

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.