1. The problem statement, all variables and given/known data A pipe is spinning around with angular velocity ω = 2 rad/s about its fixed end. Inside the pipe is a frictionless block that is free to slide. The block is located 1 m from the fixed end of the pipe when the angle from the vertical, θ = π/2 (horizontal). What is the radial acceleration of the block at this instant? 2. Relevant equations 3. The attempt at a solution My immediate intuition is that there is no acceleration along the pipe, but how do I show that? I tried to draw a FBD but I can't even come up with any forces to write on it. There is no centripetal force, there is no friction... there is nothing. It's sort of like 2.33 on here https://www.slideshare.net/anshukg/an-introduction-to-mechanics-daniel-kleppner-solutions-part1 But I'm not really able to follow the solution there.