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10/11/11

10/11/11. What can force cause? Change usually in motion. Chapter 4. Section 1 Changes in Motion. Force. A force is an action exerted on an object which may change the object’s state of rest or motion. Forces can cause accelerations. The SI unit of force is the newton, N.

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10/11/11

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  1. 10/11/11 What can force cause? Change usually in motion

  2. Chapter 4 Section 1 Changes in Motion Force • A forceis an actionexerted on an object which may change the object’s state of rest or motion. • Forcescan causeaccelerations. • The SI unit of force is thenewton, N. • Forces can act throughcontactor at adistance.

  3. Chapter 4 Section 1 Changes in Motion Comparing Contact and Field Forces Click below to watch the Visual Concept. Visual Concept

  4. Chapter 4 Section 1 Changes in Motion Force Diagrams • The effect of a force depends on both magnitude anddirection.Thus, force is avectorquantity. • Diagrams that show force vectors as arrows are calledforce diagrams. • Force diagrams that show only the forces acting on a single object are calledfree-body diagrams.

  5. Chapter 4 Section 1 Changes in Motion Force Diagrams, continued Free-Body Diagram In a force diagram,vector arrows represent all the forces acting in a situation. Force Diagram • A free-body diagramshows only the forces acting on the object of interest—in this case, the car.

  6. Chapter 4 Section 1 Changes in Motion Drawing a Free-Body Diagram Click below to watch the Visual Concept. Visual Concept

  7. Chapter 4 Section 2 Newton’s First Law Newton’s First Law • Anobject at rest remains at rest, and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line) unless the object experiences a net external force. • In other words, when the net external force on an object is zero, the object’s acceleration (or the change in the object’s velocity) is zero.

  8. Chapter 4 Section 2 Newton’s First Law Net Force • Newton's first law refers to thenet forceon an object.Thenet forceis thevector sumof all forces acting on an object. • The net force on an object can be found by using the methods for finding resultant vectors. Although several forces are acting on this car, the vector sum of the forces is zero. Thus, the net force is zero, and the car moves at a constant velocity.

  9. http://www.cleanvideosearch.com/media/action/yt/watch?videoId=ijpH6an-JIQhttp://www.cleanvideosearch.com/media/action/yt/watch?videoId=ijpH6an-JIQ

  10. Textbook page 124 • Answer Practice Problem A # 1& 2

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