2. F = ma

3. “The Force” “An energy field created by all living things. It surrounds us, penetrates us, and binds the galaxy together.” “An energy field created by all living things. It surrounds us, penetrates us, and binds the galaxy together.” The Force has two components: The Force has two components: Light side Light side Dark side Dark side

4. The Real Force Something that causes an object’s motion to change (causes acceleration). Something that causes an object’s motion to change (causes acceleration). A “push” or a “pull.” A “push” or a “pull.” Common Examples of forces: Gravity fields, pushing on something, compressing a spring, a magnetic field, tension, friction, and the “normal” force. Common Examples of forces: Gravity fields, pushing on something, compressing a spring, a magnetic field, tension, friction, and the “normal” force. Units are Newtons (N) Units are Newtons (N)

5. An object at rest remains at rest, and an object in motion continues in motion with constant velocity unless the object experiences a net external force. First Law of Motion: “The Law of Inertia” What does this law tell us? Objects in equilibrium do not accelerate. Static equilibrium (rest) and equilibrium (constant velocity) are both the result of an object with zero net force. click for web page click for applet

6. Galileo’s Unique Idea Objects don’t need a force to keep moving! Objects don’t need a force to keep moving! Every object naturally wants to maintain its state of motion or rest Every object naturally wants to maintain its state of motion or rest INERTIA! (resistance to change in motion) INERTIA! (resistance to change in motion) Refined by Newton in 1800’s: Refined by Newton in 1800’s:

7. Basic Info: Inertia Inertia depends on: Inertia depends on: Mass Mass Shape/Mass Distribution of object- rotational inertia Shape/Mass Distribution of object- rotational inertia Solid Cylinder (like a wheel of cheese,) Solid Cylinder (like a wheel of cheese,) Hoop (like a bicycle tire) Hoop (like a bicycle tire) Inertia does NOT depend on: Inertia does NOT depend on: Velocity/Speed of object Velocity/Speed of object It takes the same amount of force to speed a bus up as to slow it down! It takes the same amount of force to speed a bus up as to slow it down!

8. The Definition of Force Forces are not directly observable, but the effect of force is perceived. Newton’s Second Law defines force. A newton is defined as the force required to accelerate one kilogram of mass at a rate of one meter per second squared. A newton is the metric equivalent of the pound. Both are units of force, not mass. A newton converts to a little less than a quarter pound. “If you insist upon a precise definition of force, you will never get it!” - Richard Feynmann

9. Mass versus Weight Weight is defined as a force caused by gravity acting on a mass. Mass is classical defined as an amount or quantity of matter. The modern definition is the amount of inertia object possesses. Mass is universal; it doesn’t depend on location. Weight is local; it depends on gravity. Mass Weight massforce Metrickilogramnewton Britishslugpound

10. A contact force, often called a support force, that acts perpendicular to the surfaces in contact. Normal Force, F n A pulling force in strings, ropes, cables, etc. Tension, F T Normal Force, Tension, and Applied Force On a level surface, the normal force will balance the weight of an object, as long as no other forces act vertically. Normal means perpendicular. Tension force always pulls away from a mass (opposite of compression). FnFn PHYSICS F g = mg PHYSICS FTFT rope Applied Force, F a An applied force is any external force. PHYSICS FaFa

11. Friction Forces A contact force that always acts parallel to the surfaces in contact, and always opposes motion. FaFa PHYSICS FfFf FaFa FfFf velocity Friction arises from molecular bonding between surfaces FfFf book pulled wheel driven book dragged

12. Basic Info: Force Diagrams Definition: A Diagram that shows all the forces acting on a body Definition: A Diagram that shows all the forces acting on a body Does NOT include forces exerted by the body! Does NOT include forces exerted by the body! Forces are drawn as vectors. Forces are drawn as vectors.

13. Free Body Diagram Simple drawing of all forces working on an object or system Simple drawing of all forces working on an object or system Use a box or dot to represent the object or system Use a box or dot to represent the object or system All forces move away from the box. All forces move away from the box. The size of the arrow needs to be proportional to the size of the force. The size of the arrow needs to be proportional to the size of the force. Remember: gravity will always affect an object and so Fg will always be in a F.B.D! Remember: gravity will always affect an object and so Fg will always be in a F.B.D!

14. Free Body Diagrams A free body diagram identifies all action forces on an object so that the resultant force can be determined. Balanced Forces When the sum of all forces is equal to zero the object does not accelerate (at rest or constant velocity). When the sum of all forces is not equal to zero, the object accelerates in the direction of the resultant force. FaFa PHYSICS FsFs FaFa FkFk acceleration FnFn FgFg Unbalanced Forces FnFn FgFg click for web page