1. Good morning! Prepare to carefully record information on this very important lesson.

3. Part i: The Legend  Newton’s 1 st Law states If F NET = 0, then a = 0! This means two things….  First:  If all forces are balanced, an object at rest will remain at rest.  Secondly:  If all forces are balanced, an object in motion will continue moving with a constant velocity.

4.  Newton’s 1 st Law is also known as the law of inertia  Inertia is an object’s resistance to a change in its motion  Inertia is an inherent quality of an object  More mass ==> more inertia

5. Part II: The Characters  A force is any push or pull on an object. All forces are interactions between two objects.  The unit for force is the Newton (N)  Types of Forces:  Weight (F g ): the force due to gravity; defined as F g = mg  MASS (kg) IS NOT THE SAME AS WEIGHT (N)!  Normal (F N ): the force perpendicular to a surface (usually a supporting force, but not necessarily)  Friction (F FR ): a force that resists motion resulting from two surface in contact  Tension (F T ): the force resulting from a string, rope, etc. acting on an object  Applied (F A ): a force applied by another object

6.  Whoa! We need to have a way to organize our information about forces acting on an object!  Never fear, Free Body Diagrams are here!  A Free Body Diagram (FBD) is used to identify all the forces acting ON an object.  A FBD is used to: 1.LABEL the forces acting on an object 2.DETERMINE which forces cancel out 3.FIND the remaining force on an object, which is called the net force Part iII: The Hero

7.  Draw a Free Body Diagram of the forces acting on a 3 kg physics book sitting on a desk with you pushing on it with a 2 N force horizontally, if the book is moving with a constant velocity.  Compare your FBD with your table partners Interlude

8. Here are some important rules for using FBDs: 1)Draw the object as a box or large dot (generally) 2)Indicate all forces acting on the object with arrows going away from the object’s center. 3)Arrow length represents the relative magnitude of the force 4)ALWAYS label the types of force 5)Remember: Forces are measured in NEWTONS (N)!! Part iV: The Decree FTFT FgFg

9. 1.Draw a FBD for YOU sitting in your seat Epilogue FNFN FgFg

10. Let’s check: FBD for a 3 kg physics book sitting on a desk with you pushing on it with a 2 N force horizontally, where it is moving with a constant velocity. (a = 0, F NET = 0 N) FNFN FgFg FAFA = 30 N = 2 N = (3 kg) (10 m / s 2 ) = 30 N F fr =2 N

11. More Free Body Diagrams! Look at the 1 kg mass hanging on a string. I pull down with a force of 12 N. Draw the resulting FBD. FTFT FgFg FTFT = 12 N = (1 kg) (10 m / s 2 ) = 10 N = F g + F T = 10 N + 12 N = 22 N

12. True or False? See the Free body diagram.  This object must be moving to the right.

13.  Fun with Free Body Diagrams will be a big part of your Physics Life!  Always draw the FBD even if the problem doesn’t ask you to. The Story Continues…

14. Your tasks today:  Glue/Tape both FBD sheets into Journal  Complete Free Body Diagram Practice #1-10  Show me and get a stamp.  Go to one of the lab stations and correct your work.  Get an Exit Slip. Complete and hand in before leaving today.