AST101H5 Lecture Notes - Lecture 4: Angular Diameter, Escape Velocity, Potential Energy
Document Summary
Tides = stretch of a body due to gravity varying as 1/d^2, a universal effect. Water on earth flows following the stretched shape. A spinning object must constantly work to adjust its stretch toward the object causing the stretch = tidal friction. Earth is slowing down because of the tidal energy loss our day is getting longer by 0. 002 seconds every century. Four billion years ago the young earth"s day was only 5-6 hours. Earth has created tides on the moon, which forced its spin to synchronize with its orbit, freeing the moon from any further adjustment. Recall angular momentum is conserved m x v x r = constant. Tides decrease rotation speed, v, but earth"s mass and radius stay the same. (m and r constant, v changes) Angular momentum is transferred from earth & moon rotation to the moon"s orbit. (m x v(spin) x r ) + (m x v (orbit moon) x r (orbit) = constant.
