Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Motion and Newton’s first law What is a force? Identifying forces Newton’s second law Free-body diagrams Newton’s third law Chapter 4 Forces and Newton’s Laws of Motion Topics: Sample question: These ice boats sail across the ice at great speeds. What gets the boats moving in the first place? What keeps them from going even faster? Slide 4-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 4.An action/reaction pair of forces A.point in the same direction. B.act on the same object. C.are always long-range forces. D.act on two different objects. Slide 4-6

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 4.An action/reaction pair of forces D.act on two different objects. Slide 4-7 Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. What Is a Force? A force is a push or pull.... acts on an object.... requires an agent.... is a vector.... is a contact force or a long-range force. Slide 4-10

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Galileo ( ) Developed the idea of experimental science Re-examined natural motion of objects and how objects move Made astronomical observations that challenged Earth-centered solar system model.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton ( ) Newton's work based on experiments of how objects interact. His laws of motion and law of gravity described how all objects interact with each other.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 2-34 Newton’s Zeroeth Law of Motion Objects are dumb - They have no memory of the past and cannot predict the future. Objects only know what acts directly on them in a given moment.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton's Zeroeth Law of Motion DEMO - Pushing the cart on track

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 2-34 Identifying Forces: Freebody (Force) Diagrams and System Schema

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Free-Body Diagrams Slide 4-24

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. System Schema Draw a diagram where you write down the name of each object in the system and then draw a solid circle drawn around it. Draw two sided arrows like this between the object circles of objects that interact (This illustrates all interactions between the objects in this diagram). Draw an additional dotted line around the block to indicate it is the object of interest. This diagram is called a system schema. A system schema illustrates all the relevant interactions between the objects in a given physical situation

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton's First Law of Motion Every object continues in a state of rest or a state of motion with a constant speed in a straight line unless acted on by an unbalanced force.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton's First Law of Motion DEMO - Air Puck motion DEMO - Smash the HAND DEMO - Tablecloth

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. What Causes Motion? In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.” Slide 4-8

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton’s Second Law Slide 4-22

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Normal Force Slide 4-15