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Free Body Diagrams. Notes . Force. A force is a push or a pull. Force is not a thing in itself, but rather an interaction between two objects . Force is a vector quantity… direction matters in the answer!. Common Forces. Common Forces. Net Force.
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Free Body Diagrams Notes
Force • A force is a push or a pull. • Force is not a thing in itself, but rather an interaction between two objects. • Force is a vector quantity… direction matters in the answer!
Net Force • Net force is the vector sum of ALL forces acting on an object. • If there is zero net force, then there is zero acceleration (constant velocity), this is a special case called equilibrium. • If there is a net force, there will be an acceleration. That means that the object will be speeding up, slowing down, or changing direction.
Free Body Diagrams • A Free Body Diagram is a simple drawing that shows the magnitude and direction of all of the force vectors acting on an object. • The length of the arrows in relation to each other is VERY important • Each arrow must point away from the “free body” and be labeled appropriately • The system, the object the force is applied to, is drawn as a shaded circle
Free Body Diagrams • Here is an example of a FBD of a book at rest on a table top. • Fg is acting downward but is “balanced” by FN acting upward. • Results in no net force and zero acceleration FN The book is drawn as a ball Fg
Free Body Diagrams • Here is an example of a FBD of a box being pulled by a rope at a constant speed on a flat surface. • Fg and FN are still opposite and equal. • FT and Ff are also opposite and equal. FN Ff FT Fg Object is in motion, but not accelerating
Free Body Diagrams • Here is an example of a FBD of a ball under free fall conditions. • Fg is the only force acting on this object. • The net force is down and the object is accelerating. Fg Object is in motion and accelerating
Questions to Try Draw a FBD for the following situations: A flowerpot falls freely from a windowsill. (Ignore any forces due to air resistance.) A sky diver falls downward through the air at constant velocity. (The air exerts an upward force on the person.) A cable pulls a crate at a constant speed across a horizontal surface. The surface provides a force that resists the crate’s motion. A rope lifts a bucket at a constant speed. (Ignore air resistance.) A rope lowers a bucket at a constant speed. (Ignore air resistance.)
Answers #1 #2 Ff Fg Fg
Answers to HW #3 #4 FT FN Ff FT Fg Fg
Answers to HW #5 FT Fg
Project • Complete the practice FBD that I provided for you. • Do Not forget your Poster Board on Friday