Inertia vs. Momentum: Which Keeps You Moving? Science is real. Science is cool. Science uses a lot of terms that we all think we know. But, do we really know what we are talking about? In the spirit of scientific community and understanding, let’s clear up one big scientific misconception that we all get wrong … Pop quiz: Is it momentum or inertia that keeps you moving? Here’s a hint: In science, inertia is “the property of matter that stays at rest or continues moving in a straight line, so long as it’s not acted upon by an external force.” As a side note, this is also Newton’s First Law of Motion (file that away for trivia night). Momentum is a term that describes “the motion of an object equal to the product of its mass and its velocity.” Saying something has momentum means it’s moving in a specific direction and has a particular mass. The answer is … So, inertia describes an object’s resistance to change in motion (or lack of motion), and momentum describes how much motion it has. Pop quiz answer: Momentum is your force or speed of movement, but inertia is what keeps you going. The car had a change in motion (or momentum), but the giraffe resisted that change. Ouch. Still confused? That car resisted the change in motion (momentum) of the truck. It’s inertia kept it still. In other words … Funny Online Pictures Want to know more? Do you need to know (can’t stop, won’t stop) more about inertia, momentum, and other Einstein-y physics concepts you are intrigued about. Our friends at Study.com have you covered with their Physics courses. Check ’em out. Don't Get Mixed Up Again! Get Dictionary.com tips to keep words straight ... right in your inbox. Email address* Valid email addressPhoneThis field is for validation purposes and should be left unchanged.