Inference or observation? i think this rock is igneous bc it has intergrown crystals.

Inference, as you are using something you can observe about the object to *INFER* another thing — you observed the presence of intergrown crystals and inferred that the rock was igneous.

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on