1. Force and Newton’s Laws Pushing and Pulling

2. Essential Questions  What relationships exists among force, mass, speed, and acceleration?  What evidence indicates a force has acted on a system? Is it possible for a force to act on a system without having an effect?

3. Force  Force: A push or a pull in a direction. Force is measured in Newtons (N)

4. Common Forces  Friction: a contact force between two objects sliding together.  Air Resistance: Friction between air and objects.  Gravity: A non-contact attraction force between objects that have mass.  Larger mass = larger gravity  Smaller distance = larger gravity

5. Forces  Balanced Forces: Two or more equal forces acting on an object. Object is either not moving or traveling at a constant velocity.

6. Forces  Unbalanced Forces: Two or more unequal forces acting on an object. Unbalanced forces change the speed or direction of an object (velocity).

7. Newton’s Laws of Motion  Law 1: If the total force acting on an object is zero the objects motion does not change. (-)50N 50N

8. Newton’s Law of Motion  Law 2: Acceleration = Force / mass Force = (Mass)(Acceleration) Mass = Force / Acceleration

9. Newton’s Law of Motion  Law 3: For every action there is an equal and opposite reaction.  http://www.youtube.com/watch?v=UARB HORBhC8&feature=related

10. Free body Diagrams  A free body diagram shows the forces acting on an object.

11. Example 1  A student in a random middle school science class angers his teacher and is suspended from the ceiling by his toe nails. He remains there for two days until his nails fall out and he crashes to the floor. What forces are acting on the student? Rope (tension) Gravity

12. Example 2  Police are chasing a student who stole their teacher’s bicycle. The forces are labeled with arrows, but you must give them names. What does each arrow represent? Gravity Air ResistanceBiker/Student Normal Force