Chapter 4 Notes: The Laws of Motion Forces Force ? push or pull on some object vector quantity Contact Forces ? result from physical contact between two objects Field Forces ? ?action-at-a-distance? gravity electric force magnetic force * The known fundamental forces in nature are all field forces In order of decreasing strength: strong nuclear force electromagnetic force weak nuclear force gravitational force Newton?s First Law An object moves with a velocity that is constant in magnitude and direction, unless acted on by a nonzero net force Net Force ? vector sum of all external forces exerted on an object Mass and Inertia Inertia ? tendency of an object to continue in its original state of motion Mass ? measure of an object?s resistance to changes in its motion due to force