114 h5p Samples

Newton’s first law of motion is probably the hardest to understand.  It includes the very counterintuitive idea that it does NOT require a force to keep an object moving.  In the absence of any forces, a moving object will continue moving forever, traveling at a constant speed and in a constant direction (in a straight line).  Moving things on Earth eventually come to a stop… because of friction, because they run into something, because they hit the ground… but they don’t continue traveling forever.  In all of these cases, there is a force that brings them to a stop.  Absent a force, they would keep moving.

Newton used this idea when developing his explanation for the planets’ orbits.  Consider the following thought experiments.