# ch.5, sec.2 – what is a force?

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force : a push or a pull exerted on an object in order to change the motion of the object; force has size & direction. Ch.5, Sec.2 What Is A Force?. newton : the SI unit for force and weight (N). Forces Acting on Objects. - PowerPoint PPT Presentation

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Ch.5, Sec.2 What Is A Force?

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 & directionnewton: 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 Earths gravity pulls the atmospheric gases closer to its surface!Ch.5, Sec.2 What Is A Force?Determining Net Forcenet 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?7 N north5 N south=2 N northCh.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 movingCh.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