The Earth’s gravity pulls the atmospheric gases closer to its surface! Ch.5, Sec.2 – What Is A Force? force: a push or a pull exerted on an object in order to change the motion of the object; force has size & direction newton: the SI unit for force and weight (N) Forces Acting on Objects - not all forces can be seen and forces can only act on objects with matter - gravity & magnetism are sometimes hard to see! The Earth’s gravity pulls the atmospheric gases closer to its surface!

Ch.5, Sec.2 – What Is A Force? Determining Net Force net force: the combination of all the forces acting on an object - calculating net force is determined by the direction in which the forces are placed - If one person applies 8 N of force to a book and another person applies 6 N of force (in the same direction), then the book requires 14 N of force to be moved!

Ch.5, Sec.2 – What Is A Force? - If one person applies 20 N of force to a book and another person applies 18 N of force (in the opposite direction), then the book will have 2 N of force pushing it to the left! - What is the net force of an object when you combine a force of 7 N north with a force of 5 N south? 5 N south = 2 N north 7 N north

Ch.5, Sec.2 – What Is A Force?

Ch.5, Sec.2 – What Is A Force? Balanced & Unbalanced Forces - net force is important because it tells us whether the forces on an object are balanced or unbalanced - when the net force on an object is 0 N, the forces are balanced! - balanced forces will not cause an object to change its motion - balanced forces will not cause an unmoving object to start moving

Ch.5, Sec.2 – What Is A Force? - when the net force on an object is not 0 N, the forces are unbalanced! - unbalanced forces cause a change in motion, such as speed or velocity - unbalanced forces are necessary to cause an unmoving object to start moving