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Lesson 11 – Forces and FBD’s

Lesson 11 – Forces and FBD’s. August 14, 2013. Learning Goals. The student will be able to identify forces The student will be able to analyze forces acting on a body, with the use of FBD The student will use rectangular components to find the resultant force. Force of Gravity.

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Lesson 11 – Forces and FBD’s

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  1. Lesson 11 – Forces and FBD’s August 14, 2013

  2. Learning Goals • The student will be able to identify forces • The student will be able to analyze forces acting on a body, with the use of FBD • The student will use rectangular components to find the resultant force

  3. Force of Gravity • What is the force of gravity?

  4. Normal Force Professor David Harrison Physics at University of Toronto • What is a normal force? • A book is at rest on a desk. Which statement is true? • The normal force balances the force of gravity • The normal force and gravity both point downwards • Gravity is the only force acting on the book • The normal force is the only force acting on the book

  5. Tension Force • What is the tension? • A force between two colliding objects such as a puck and a hockey stick • Measured using a beam balance • A pushing force exerted by a string or rope • A pulling force exerted by a string or rope • How does a frictionless pulley affect tension? Professor James Fraser Physics at Queens University

  6. Friction • What is Fk and Fs responsible for? Compare and contrast the two • What is providing the force of friction on objects? • Which statement is true about friction? • It can exist between objects that are not in contact • It makes sliding one object over another easier • It resists the sliding motion between objects • It is a pulling force exerted by a string or rope

  7. Friction • Which statement is true about kinetic friction? • It exists between two forces in contact at rest with respect to each other • It is a force exerted on a moving object by a surface opposite to the direction of motion • It keeps a box resting on the floor from moving • It is a force exerted on a moving object by a surface in the same direction as the motion

  8. Air Resistance • How are air resistance and friction related? • Which statement is true about air resistance? • It must always be taken into account in a problem-solving situation • It is a form of kinetic friction • It is a form of static friction • It is exerted against the air by an object moving through it

  9. Applied Force • What is an applied force? • Which of these is an example of an applied force? • The static friction between your shoes and the ground • The kinetic friction on a skier sliding down a slope • The tension in a clothesline holding clothes for drying • A child pushing another child on a swing at the park

  10. Free-Body Diagrams • What are the key features in a FBD? Professor Eric Mazur Physics at Harvard University

  11. Resultant Force Professor Tom Russell Physics at Queen’s University • What does the net force represent?

  12. Resultant Force Example 1 The force of gravity on a basketball is 16 N [down]. • What is the net force on the ball while held stationary in your hand? • (ans. 0 N) • Neglecting air resistance, calculate the net force acting on the ball if you suddenly remove your hand. • (ans. 16 N [down]) • You push the ball with a force of 12 N [right]. Calculate the net force on the ball. • (ans. 20 N [right 53° down]) • You push the ball with a force of 26 N [up 45° right]. Calculate the net force on the ball. • (ans. 19 N [right 7.4° up])

  13. Resultant Force Example 2

  14. Example 2 Continued ..

  15. Example 2 Continued …

  16. Example 2 Continued …….

  17. Required Before Next Class • Read Section 2.1 • Read Section 2.2 • Pg. 68 # 3, 4 • Pg. 69 # 6, 7, 8

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