1. Honors Physics Newton’s Second Law of Motion

2.  Newton’s First Law explains the results of zero net external force. –The body stays at rest or moves with constant velocity.  What happens if there is a net external force?  The body’s state of motion changes.  The Second Law gives the specifics.

3. Behaviors  When a net external force is exerted on an object the object will accelerate.  Consider two situations: –A body of constant mass on which the net external force is increased. –A body with increasing mass on which the net external force remains constant.

4. Constant Mass  What happens to the acceleration as the external force is increased?  The acceleration increases.  In what direction does the cart accelerate with respect to the external force?  The same direction.  So the acceleration is directly proportional to and in the same direction as the net external force.

5. Constant Force  What happens to the acceleration as the mass is increased but the force is held constant?  The acceleration decreases.  The acceleration is inversely proportional to the mass of the object.

6. Newton’s Second Law  If a net external force is exerted on an object, the object will accelerate in the direction of the net external force. The acceleration is directly proportional to the magnitude of the net external force and inversely proportional to the mass of the object.

7. Mathematical Statement

8. Units and Free-Body Diagrams  Force is measured in Newtons (N)  It takes 1 Newton of force to accelerate a 1 kg object at 1 m/s 2  Free-Body diagrams –A simple dot is used to represent the object. –Arrows are drawn to represent the forces acting on the on that body.

9. Discussion and Examples  Assigned Questions –#’s 2, 3, 4, 7, 8  Problem #6  Problem #15  Problem #17