Why are some rocks smooth and others rough?

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1

Observations show that interstellar clouds can have almost any shape and

Diego is trying to lift a piano to the second floor of his house. diego uses a pulley system and gives a big lift to the piano.the piano moves upward, then stops, and then it starts to fall to the ground. which list best describes the forces on the piano in the proper order? positive force → balanced force → negative force negative force → balanced force → positive force positive force → unbalanced force → negative force negative force → unbalanced force → positive force