Newton's first law of motion
The first law of motion is the motion of an object that will remain the same (either at rest or moving at a constant speed in a straight line) in the absence of unbalanced forces; if a change in motion is observed there must be a net force on the object. Simply put, the objects at rest stay at rest and the objects in motion stay in motion unless an external net force acts on the object.
I am driving by and I notice a turtle on the sidewalk laying on it's back, it's unable to flip back on it's stomach so it can walk. I parked my car and decided to try to help it out, it was stuck and was afraid so it went back in it's shell. If I had not pushed it over with my force it would have stayed there helpless, it walked away after I did push it over. This is a great example of Newton's law because if I had left it there nothing would have moved it over unless if someone else did the same way I did.