 Force: A push or a pull Describes why objects move Defined by Sir Isaac Newton

Newton’s Laws  Newton’s First Law: An object at motion stays in motion unless acted upon by a net force In other words: no net force means no change in motion.

 Newton’s 2 nd Law: F = ma Measured in Newton’s ○ 1 N = 1 kg * m/s 2

 Newton’s 3 rd Law: When an object exerts a force on a second object, the second exerts a force equal in magnitude but opposite in direction to the first. ○ Action-reaction forces

Types of Forces  Gravity: considered to be straight downward. Symbolized F g or W Also called Weight F g =

 Normal Force: force perpendicular to the surface of contact between two surfaces. The force of contact between 2 surfaces.

Net Force  Net force is the sum of all forces acting on an object in a particular direction.  F net = mass of object * actual acceleration of the object in that direction  No acceleration means net force = 0 N Constant velocity, object at rest Equilibrium

Free-Body Diagrams  Simple sketches that show all forces acting on an object.

 You and a friend push a large box across the floor. You push with a force of 100 N, your friend pushes with a force of 85 N. The force of friction on the box is 40 N. The box has a mass of 60 kg. Draw a free body diagram showing all forces acting on the box. Determine the net force acting on the box. What will be the acceleration of the box? How far will the box have moved after 3 seconds?

Finding net force/acceleration  A 14 kg box is being pulled up a ramp inclined at 27 degrees above the horizontal with a force of 140N. The force of friction acting on the box is 35 N. What will be the acceleration of the box?

Homework  Pg. 124 #1-2 Practice A  Pg. 128 #1-3 Practice B  Pg. 129 #1-5 Section Review

 Friction: the force that opposes motion between 2 surfaces.