At the local playground, a 16-kg child sits on the end of a horizontal teeter-totter, 1.5 m from the pivot point. On the other side of the pivot an adult pushes straight down on the teeter-totter with a force of 95 N. In which direction does the teeter-totter rotate if the adult applies the force at a distance of (a) 3.0 m, (b) 2.5 m, or (c) 2.0 m from the pivot?
Modern Physics Lecture 1: Foundations and Special Relativity Position, Time, and Rotation are all continuous symmetries (discrete symmetries such as reflection do not produce the same results as below): Invariance in position (changing where in space you perform your experiment) proves momentum conservation Invariance in rotation (eg. rotating your entire experiment by 90 degrees) proves conservation of angular momentum Invariance in time (changing when in time you perform your experiment, eg. today vs. tomorrow) proves energy conservation Newtonian Mechanics: Inertia F=ma The force of object 1 on object 2 is equal in magnitude to the force of object 2 on object 1 True in an inertial reference frame