Final answer:
The kind of change happening when tree roots push up cement on a sidewalk is mechanical weathering. Tree roots grow and expand, exerting pressure and causing cracks in the cement. This phenomena is called bioturbation.
Step-by-step explanation:
The kind of change that is taking place when tree roots are pushing up cement on a sidewalk is called mechanical weathering. Mechanical weathering refers to the physical breakdown of rocks and minerals into smaller pieces without any chemical change. In this case, the roots of the tree grow and expand, exerting pressure on the cement, causing it to crack and break.
Tree roots can also cause displacement of the cement. As the roots grow, they can apply force on the cement and lift it up, creating uneven surfaces on the sidewalk.
Another term related to this phenomenon is bioturbation, which refers to the disturbance or alteration of soil by living organisms. In this case, the tree roots are bioturbating the cement, causing it to break and move.