Hello, this thought i'm having might be difficult to explain, but i will do my best. Ever since i learned about conservation of energy, conservation of mass (or mass plus energy due to E=mc^2) and conservation of linear/angular momentum, i always found it weird that things in nature can change to a diferente state, but still conserve all these quantities. Lets consider that i'm on the floor at position x=0 I start moving at 1 m/s for 5 seconds, meanwhile earth begins moving backward in order to conserve linear momentum. When i stop at x=5, both me and earth stop so that momentum remains conserved. My first question, is why can i stop after i start moving, what is involved here? Is it that once i stop moving my feet adhere to the ground and force me and earth to reach a stable state of zero velocity for both? This something i don't quite know how to explain, am i far from the true answer? Also, in order for me to start moving, i have to spend energy. Where has this energy gone once i stop moving? Should it return to me since i stopped moving and linear momentum got conserved? If the energy does not return, will nature somehow cause me to return to my initial position using that energy? This last point might seem strange, but i've been wondering about it, does nature also eventually lead things to the original state? Say the situation where i was at x=0 by somehow using the energy i spent to move in order to return me to my original position?