1. Forces and Force Diagrams 4.1 pp. 124 - 128 Mr. Richter

2. Agenda  Warm Up  Notes:  That’s a Force!  Units of Force  Types of Forces  Force Diagrams  Tests Back

3. Objectives: We Will Be Able To…  Explain how force affects the motion of an object.  Distinguish between contact forces and field forces.  Interpret and construct free-body diagrams (FBDs)

4. Warm-Up:  A car is driving down a flat roadway to the right. What forces do you think are acting on the car (there are at least 4)? What direction do these forces go?  Draw a sketch of a car, and then draw arrows to represent each force you think is present.

5. Force

6.  Force is a push or a pull acting on an object.  Another way of thinking is that a force changes an object’s velocity.  Force can speed up an object or slow it down.  Force can change an object’s direction.  Force causes acceleration (more on this when we discuss Newton’s Laws of Motion)

7. Units of Force  The units of force we will most often use in physics are Newtons.  A Newton is the amount of force required to accelerate a 1-kg object 1 m/s 2.  [1 N = 1 kg*m/s 2 ]  In the British system, the pound is the unit of force.  1 pound = 4.448 N

8. Types of Force  All forces can be broken up into two categories.  Contact force is force that arises from the physical contact between two objects.  catching a baseball, speeding up a car, etc.  Field force is force that exists in the absence of physical contact.  gravity, magnetic force, etc.  Is air resistance a contact force or a field force?

9. Force Diagrams

10.  Force is a vector quantity, meaning that it has both magnitude and direction.  In complex situations (like a car crashing into a wall), force diagrams help physicists to analyze the situation.

11. Free-Body Diagrams (FBDs)  To determine the effects of all of the forces acting on one object, a free-body diagram (FBD) is drawn.  Only the forces ACTING ON THE OBJECT are drawn, pointing in the directions in which they act.

12. FBD Example  Consider the forces acting on the car in the tow truck below.

13. FBD Practice  Sketch the FBD for the following two situations: 1.A book lying on a flat table. 2.A book lying on a ramp with an incline of 15°

14. Wrap-Up: Did we meet our objectives?  Explain how force affects the motion of an object.  Distinguish between contact forces and field forces.  Interpret and construct free-body diagrams (FBDs)

15. Homework  p. 128 #2, 3, 5 and 6  Science Fair  Notebook and Research due Wednesday  Rough draft of Procedure due Wednesday 12/5