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? 7 N north

5 N south

= 2 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