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Free-Body Diagrams

Free-Body Diagrams. October 31, 2013. Thursday, 10/31. Happy Halloween! Use your notes to solve the following: Find the weights of these objects: 1. 1800 kg car 2. 0.12 kg baseball Upcoming Events: Open note quiz – Wednesday, 11/6 Unit 4 Test – Wednesday, 11/12.

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Free-Body Diagrams

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  1. Free-Body Diagrams October 31, 2013

  2. Thursday, 10/31 • Happy Halloween! • Use your notes to solve the following: • Find the weights of these objects: 1. 1800 kg car 2. 0.12 kg baseball Upcoming Events: • Open note quiz – Wednesday, 11/6 • Unit 4 Test – Wednesday, 11/12

  3. Unit 4: ForcesFree-Body Diagrams • Vector Review • A vector has magnitude and direction (ex. Velocity) • The magnitude of the vector quantifies how large it is. • Arrows are used to depict a vector (size and direction) • Force is a vector • Magnitude – amount of force in Newtons (N) • Direction is depicted with an arrow

  4. Unit 4: ForcesFree-Body Diagrams • Free Body Diagrams are… • Are a pictorial representation of forces acting on an object. • Are used to show the magnitude and direction of all forces acting on an object. • The size of the arrow reflects the size of the force • The arrow shows the direction the force is acting • Force is a vector • Magnitude – amount of force in Newtons (N) • Direction is depicted with an arrow

  5. Unit 4: ForcesFree-Body Diagrams Steps for drawing Free-body diagrams • Replace the object with a dot or box. • Identify all the long-range forces acting on the object (ex. Gravity) • Identify all the contact forces acting on the object. • Remember that only something that is physically touching the object can apply a contact force • Possible types of contact forces – push, tension, normal, and friction

  6. Unit 4: ForcesFree-Body Diagrams Things to remember when working with force diagrams: • Always follow all 3 steps • Force due to gravity acts on all objects and always points down • Force arrows must originate from the dot, this means that you will never have an arrow pointing at the dot, always away from the dot • Surfaces apply a normal force that is always perpendicular to the surface.

  7. Example 1: A book is at rest on a tabletop

  8. Example 2: A girl is suspended motionless from the ceiling by two ropes

  9. Example 3: An egg is free-falling from a nest in a tree. Neglect air resistance.

  10. Example 4: A Flying squirrel is gliding from a tree to the ground at a constant velocity. Consider air resistance.

  11. Example 5: A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. A free-

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